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recent spacecraft and radar observations found that ∼70% of short-period comet nuclei, mostly jupiter-family comets (jfcs), have bilobate shapes (two masses connected by a narrow neck). this is in stark contrast to the shapes of asteroids of similar sizes, of which ∼14% are bilobate. this suggests that a process or mechanism unique to comets is producing these shapes. here we show that the bilobate shapes of jfc nuclei are a natural byproduct of sublimative activity during their dynamical migration from their trans-neptunian reservoir, through the centaur population, and into the jupiter family. we model the torques resulting from volatile sublimation during this dynamical migration, and find that they tend to spin up these nuclei to disruption. once disrupted, the rubble pile-like material properties of comet nuclei (tensile strengths of ∼1-10 pa and internal friction angles of ∼35°) cause them to reform as bilobate objects. we find that jfcs likely experienced rotational disruption events prior to entering the jupiter family, which could explain the prevalence of bilobate shapes. these results suggest that the bilobate shapes of observed comets developed recently in their history (within the past ∼1-10 myr), rather than during solar system formation or collisions during planet migration and residency in the trans-neptunian population. | the formation of bilobate comet shapes through sublimative torques |
context. high-mass star formation is a hierarchical process from cloud (>1 pc), to clump (0.1−1 pc), to core scales (<0.1 pc). modern interferometers that achieve high angular resolutions at millimeter wavelengths allow us to probe the physical and chemical properties of the gas and dust of protostellar cores in the earliest evolutionary formation phases.aims: in this study we investigate how physical properties, such as the density and temperature profiles, evolve on core scales through the evolutionary sequence during high-mass star formation ranging from protostars in cold infrared-dark clouds to evolved ultracompact hii (uchii) regions.methods: we observed 11 high-mass star-forming regions with the atacama large millimeter/submillimeter array (alma) at 3 mm wavelengths. based on the 3 mm continuum morphology and h(40)α recombination line emission - which trace locations with free-free (ff) emission - the fragmented cores analyzed in this study are classified as either "dust" or "dust+ff" cores. in addition, we resolved three cometary uchii regions with extended 3 mm emission that is dominated by free-free emission. the temperature structure and radial profiles (t ~ r−q) were determined by modeling the molecular emission of ch3cn and ch313cn with xclass and by using the hcn-to-hnc intensity ratio as a probe for the gas kinetic temperature. the density profiles (n ~ r−p) were estimated from the 3 mm continuum visibility profiles. the masses (m) and h2 column densities (n(h2)) were then calculated from the 3 mm dust continuum emission.results: we find a large spread in mass and peak h2 column density in the detected sources, ranging from 0.1 to 150 m⊙ and 1023 to 1026 cm−2, respectively. including the results of the core and core-extension studies to increase the sample size, we find evolutionary trends on core scales for the temperature power-law index (q) increasing from 0.1 to 0.7 from infrared-dark clouds to uchii regions, while for the density power-law index (p) on core scales, we do not find strong evidence for an evolutionary trend. however, we find that on the larger clump scales the density profile flattens from p ≈ 2.2 to p ≈ 1.2 during these evolutionary phases.conclusions: by characterizing a large statistical sample of individual fragmented cores, we find that the physical properties, such as the temperature on core scales and the density profile on clump scales, evolve even during the earliest evolutionary phases in high-mass star-forming regions. these findings provide observational constraints for theoretical models that describe the formation of massive stars. in follow-up studies we aim to further characterize the chemical properties of the regions by analyzing the large amount of molecular lines detected with alma in order to investigate how the chemical properties of the molecular gas evolve during the formation of massive stars. | physical and chemical complexity in high-mass star-forming regions with alma. i. overview and evolutionary trends of physical properties |
in 2021 and 2022 the hydrogen comae of three long period comets, c/2020 s3 (erasmus), c/2021 a1 (leonard) and c/2021 o3 (panstarrs) were observed with the solar wind anisotropies (swan) all-sky hydrogen lyman-alpha camera on the solar and heliosphere observer (soho) satellite. swan obtains nearly daily full-sky images of the hydrogen lyman-α distribution of the interstellar hydrogen as it passes through the solar system yielding information about the solar wind and solar ultraviolet fluxes that eats away at it by ionization and charge exchange. the hydrogen comae of comets, when of sufficient brightness, are also observed. water production rates have been calculated over time for each of these comets. of particular interest are comet c/2021 o3 (panstarrs) which apparently disintegrated a few days before its perihelion at 0.28 au and c/2021 a1 (leonard) which also disintegrated beginning about 20 days after its perihelion peak. the behavior of comet c/2020 s3 (erasmus) was more typical without dramatic fading, but still was asymmetric about perihelion, with a more rapid turn on before perihelion and more extended activity well after perihelion. | water production rates from soho/swan observations of comets c/2020 s3 (erasmus), c/2021 a1 (leonard) and c/2021 o3 (panstarrs) |
context. the late phases of the orbital evolution of an earth-like planet around a sun-like star are revisited in order to consider the effect of density fluctuations associated with convective motions inside the star.aims: such fluctuations produce a random perturbation of the stellar outer gravitational field that excites a small residual eccentricity in the orbit of the planet. this counteracts the effects of tides, which tend to circularize the orbit.methods: we computed the power spectrum of the outer gravitational field fluctuations of the star in the quadrupole approximation and studied their effects on the orbit of the planet using a perturbative approach. the residual eccentricity is found to be a stochastic variable showing a gaussian distribution.results: adopting a model of the stellar evolution of our sun computed with modules for experiments in stellar astrophysics (mesa), we find that the earth will be engulfed by the sun when it is close to the tip of the red giant branch phase of evolution. we find a maximum mean value of the residual eccentricity of ~0.026 immediately before engulfment. considering an earth-mass planet with an initial orbital semimajor axis sufficiently large to escape engulfment, we find that the mean value of the residual eccentricity is greater than 0.01 for an initial separation of up to ~l.4 au.conclusions: the engulfment of the earth by the red giant sun is found to be a stochastic process instead of being deterministic as assumed in previous studies. if an earth-like planet escapes engulfment, its orbit around its remnant white dwarf (wd) star will be moderately eccentric. such a residual eccentricity of on the order of a few hundredths can play a relevant role in sustaining the pollution of the wd atmosphere by asteroids and comets, as observed in several objects. | residual eccentricity of an earth-like planet orbiting a red giant sun |
the lunar crater record features ∼ 50 basins. the radiometric dating of apollo samples indicates that the imbrium basin formed relatively late - from the planet formation perspective - some ≃ 3 . 9 ga. here we develop a dynamical model for impactors in the inner solar system to provide context for the interpretation of the lunar crater record. the contribution of cometary impactors is found to be insignificant. asteroids produced most large impacts on the terrestrial worlds in the last ≃ 3 gyr. the great majority of early impactors were rocky planetesimals left behind at ∼ 0 . 5 -1.5 au after the terrestrial planet accretion. the population of terrestrial planetesimals was reduced by disruptive collisions in the first t ∼ 20 myr after the gas disk dispersal. we estimate that there were ∼ 4 × 105 diameter d > 10 km bodies when the moon formed (total planetesimal mass ∼ 0 . 015 mearth at t ∼ 50 myr). the early bombardment of the moon was intense. to accommodate ∼ 50 known basins, the lunar basins that formed before ≃ 4 . 35 -4.41 ga must have been erased. the late formation of imbrium occurs with a ∼ 15 -35% probability in our model. about 20 d > 10 -km bodies were expected to hit the earth between 2.5 and 3.5 ga, which is comparable to the number of known spherule beds in the late archean. we discuss implications of our model for the lunar/martian crater chronologies, late veneer, and noble gases in the earth atmosphere. | early bombardment of the moon: connecting the lunar crater record to the terrestrial planet formation |
the cometary mission rosetta has shown the presence of higher-than-expected suprathermal electron fluxes. in this study, using 3d fully kinetic electromagnetic simulations of the interaction of the solar wind with a comet, we constrain the kinetic mechanism that is responsible for the bulk electron energization that creates the suprathermal distribution from the warm background of solar wind electrons. we identify and characterize the magnetic field-aligned ambipolar electric field that ensures quasi-neutrality and traps warm electrons. solar wind electrons are accelerated to energies as high as 50-70 ev close to the comet nucleus without the need for wave-particle or turbulent heating mechanisms. we find that the accelerating potential controls the parallel electron temperature, total density, and (to a lesser degree) the perpendicular electron temperature and the magnetic field magnitude. our self-consistent approach enables us to better understand the underlying plasma processes that govern the near-comet plasma environment. | a fully kinetic perspective of electron acceleration around a weakly outgassing comet |
context. the systematic investigation of comets in a wide range of heliocentric distances can contribute to a better understanding of the physical mechanisms that trigger activity at large distances from the sun and reveals possible differences in the composition of outer solar system bodies belonging to various dynamical groups.aims: we seek to analyze the dust environment of the selected nearly isotropic comets with a perihelion distance between 4.5 and 9.1 au, where sublimation of water ice is considered to be negligible.methods: we present results of multicolor broadband photometric observations for 14 distant active objects conducted between 2008 and 2015 with various telescopes. images obtained with broadband filters were used to investigate optical colors of the cometary comae and to quantify physical activity of the comet nuclei.results: the activity level was estimated with afρ parameters ranging between 95 ± 10 cm and 9600 ± 300 cm. three returning comets were less active than the dynamically new comets. dust production rates of the comet nuclei were estimated between 1 and 100 kg s-1 based on some assumptions about the physical properties of dust particles populating comae. the measured colors point out reddening of the continuum for all the comets. the mean values of a normalized reflectivity gradient within the group of the comets amount to 14 ± 2% per 1000 å and 3 ± 2% per 1000 å in the bv and vr spectral domains, respectively. the comae of the dynamically new comets, which were observed on their inbound legs, may be slightly redder in the blue spectral interval than comae of the comets observed after the perihelion passages. the dynamically new comets observed both pre- and post-perihelion, seem to have higher production rates post-perihelion than pre-perihelion for similar heliocentric distances. | physical activity of the selected nearly isotropic comets with perihelia at large heliocentric distance |
context. solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet because they mass-load the solar wind through an effective conversion of fast, light solar wind ions into slow, heavy cometary ions. the esa/rosetta mission to comet 67p/churyumov-gerasimenko (67p) provided a unique opportunity to study charge-changing processes in situ.aims: to understand the role of charge-changing reactions in the evolution of the solar wind plasma and to interpret the complex in situ measurements made by rosetta, numerical or analytical models are necessary.methods: an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines is presented. it is based on a thorough book-keeping of available charge-changing cross sections of hydrogen and helium particles in a water gas.results: after presenting a general 1d solution of charge exchange at comets, we study the theoretical dependence of charge-state distributions of (he2+, he+, he0) and (h+, h0, h-) on solar wind parameters at comet 67p. we show that double charge exchange for the he2+-h2o system plays an important role below a solar wind bulk speed of 200 km s-1, resulting in the production of he energetic neutral atoms, whereas stripping reactions can in general be neglected. retrievals of outgassing rates and solar wind upstream fluxes from local rosetta measurements deep in the coma are discussed. solar wind ion temperature effects at 400 km s-1 solar wind speed are well contained during the rosetta mission.conclusions: as the comet approaches perihelion, the model predicts a sharp decrease of solar wind ion fluxes by almost one order of magnitude at the location of rosetta, forming in effect a solar wind ion cavity. this study is the second part of a series of three on solar wind charge-exchange and ionization processes at comets, with a specific application to comet 67p and the rosetta mission. | solar wind charge exchange in cometary atmospheres. ii. analytical model |
context. we analyze the results of our comprehensive observations of the high-perihelion comet c/2014 b1 (schwartz) with stable disk-shaped coma and jets in order to study its nature.aims: the main objective of our study is to obtain new observational results for a unique disk-like comet c/2014 b1 (schwartz) with a perihelion distance of 9.56 au.methods: quasi-simultaneous long-slit spectra, as well as photometric and polarimetric images with g-sdss and r-sdss filters, were acquired with the 6 m telescope of the special astrophysical observatory on 2017 january 23. the bvr-band photometry of the comet was also performed at the 2m telescope of the peak terskol observatory on 2017 january 31. we modeled the dynamics of the jets and the behavior of the color and polarization in the coma considering the dust as aggregated large particles.results: we did not reveal any emissions in the spectra. the positions of two jets oriented along the position angles of 179° and 350° and the disk-like shape of the coma have remained unchanged for more than 4 yr. the most realistic model able to explain jets of such stable orientation includes the existence of two active sources located near the north and south poles of the rotating nucleus whose diameter was determined to be between 7.6 and 12.2 km depending on the albedo, of namely between 0.1 and 0.04, respectively. the high activity of the comet is characterized by the high dust production afρ which varied from 4440 to 3357 cm between 2017 january 23 and 31. a significant difference between the radial surface brightness profiles of the jets and the ambient (undisturbed by the jets) coma is found. the color of the jet structures is much redder than that of the ambient coma, and the nucleus has a very red color, v − r=0.93m±0.19m. there are spatial variations of the color and polarization over the coma and jets.conclusions: the observed trends in color and polarization, as well as the brightness profiles, can be explained by the fragmentation of aggregated particles formed by co2/h2o ices, silicates, and organics, which are of ~1 mm in radius near the nucleus and ~10 μm in radius at the periphery of the coma. | quasi-simultaneous photometric, polarimetric, and spectral observations of distant comet c/2014 b1 (schwartz) |
context. cyanamide (nh2cn) and its tautomer carbodiimide (nhchn) are believed to have been key precursors of purines and pyrimidines during abiogenesis on primitive earth. the detection of guanine and cytosine in meteorites and comets provides evidence of their nonterrestrial formation. although nh2cn has been found in several molecular clouds, nhchn has only been detected in sgr b2(n). their possible molecular formation mechanisms in the gas phase and therefore their respective molecular precursors remain an open subject of investigation.aims: the main objective of this paper is to determine which reactions can produce nh2cn and hncnh in the amounts observed under the astrophysical conditions of sgr b2(n). the determination of their most likely precursors could serve to provide new insights into possible routes to purine and pyrimidine synthesis, and by extension to nucleosides, under the astrophysical conditions of dense molecular clouds.methods: initially, we proposed 120 reaction mechanisms, 60 being dedicated to nh2cn formation and the remaining 60 to hncnh. these mechanisms were constructed using 25 chemical species that were identified in outer space. we calculated the molecular energies of reactants and products at the ccsd(t)-f12/cc-pvtz-f12 and mp2/aug-cc-pvdz levels of theory, and defined the values of thermodynamic functions using the maxwell-boltzmann statistical quantum theory. via an extensive literature review on the abundances of reactants and products in sgr b2(n), in addition to a detailed kinetic study for a range of 20-300 k, we identify the most likely reaction mechanisms for both cyanamides of those proposed previously and presently.results: from the 120 analyzed reactions, only nine for nh2cn and four for hncnh could thermodynamically account for their synthesis in sgr b2(n). the kinetic portion of our study shows that ra60 (ch3nh2 +·cn → nh2cn +·ch3), with a modified arrhenius expression of kt = 1.22 × 10−9 (t/300)−0.038 exp− (−147.34/t) cm3 mol−1 s−1, is the most efficient reaction at low temperatures (<60 k). above 60 k, no reaction with known reagents in sgr b2(n) is efficient enough. in this way, ra37-2 (·hncn +·nh2 → nh2cn +3nh) appears to be the most likely candidate, showing a modified arrhenius constant of kt = 2.51 × 10−11 (t/300)−32.18 exp− (−1.332/t) cm3 mol−1 s−1. in the case of carbodiimide production, rb18 (·h2nc +·nh2 → hncnh +·h) is the most efficient reaction, fitting a rate constant of kt = 4.70 × 10−13 (300/t)−3.24 exp− (36.28/t) cm3 mol−1 s−1 in sgr b2(n).conclusions: the detected gas-phase abundances of cyanamide (nh2cn) in sgr b2(n) can be explained as: ra60 (·cn +·ch3nh2) from 20 to 60 k; ra5: (·cn +·nh2) from 60 to 120 k; and ra37-2 (·hncn +·nh2) from 120 to 300 k. the carbodiimide (hncnh) synthesis could proceed via rb18 (·h2nc +·nh2). moreover, the presence of·hncn and·h2nc in sgr b2(n) are predicted here, making them viable candidates for future astronomical observations. the foreseen column density for the cyanomidil radical is ~1016 cm2 s−1 at 150 k or higher, while for amino methylidine, the value is a few 1013 cm2 s−1 at 100 k. | gas-phase molecular formation mechanisms of cyanamide (nh2cn) and its tautomer carbodiimide (hncnh) under sgr b2(n) astrophysical conditions |
this paper reviews the observations of crater-like features on cometary nuclei. we compare potential crater sizes and morphologies, and we discuss the probability of impacts between small asteroids in the main belt and a comet crossing this region of the solar system. finally, we investigate the fate of the impactor and its chances of survival on the nucleus. we find that comets do undergo impacts although the rapid evolution of the surface erases most of the features and make craters difficult to detect. in the case of a collision between a rocky body and a highly porous cometary nucleus, two specific crater morphologies can be formed: a central pit surrounded by a shallow depression, or a pit, deeper than typical craters observed on rocky surfaces. after the impact, it is likely that a significant fraction of the projectile will remain in the crater. during its two years long escort of comet 67p/churyumov-gerasimenko, esa's mission rosetta should be able to detect specific silicates signatures at the bottom of craters or crater-like features, as evidence of this contamination. for large craters, structural changes in the impacted region, in particular compaction of material, will affect the local activity. the increase of tensile strength can extinct the activity by preventing the gas from lifting up dust grains. on the other hand, material compaction can help the heat flux to travel deeper in the nucleus, potentially reaching unexposed pockets of volatiles, and therefore increasing the activity. ground truth data from rosetta will help us infer the relative importance of those two effects. | craters on comets |
cometary outbursts on several comets have been observed both by ground-based telescopes and by in situ instruments on spacecraft. however, the mechanism behind these phenomena and their physical properties are still unclear. the optical, spectrocopic and infrared remote imaging system (osiris) onboard the rosetta spacecraft provided first-hand information on the outbursts from comet 67p/churyumov-gerasimenko during its perihelion passage in 2015. the physical properties of the outbursts can be investigated by examining the time series of these high-resolution images. an analysis is made of the wide- and narrow-angle images obtained during the monitoring of the outburst sequences, which occurred between july and september in 2015. a ring-masking technique is used to calculate the excess brightness of the outbursts. the ejected mass and expansion velocity of the outbursts is estimated from differences in images made with the same filter (orange filter). the calculated excess brightness from these outburst plumes ranges from a few per cent to 28 per cent. in some major outbursts, the brightness contribution from the outburst plume can be one or two times higher than that of the typical coma jet activities. the strongest event was the perihelion outburst detected just a few hours before perihelion. the mass ejection rate during a generic outburst could reach a few per cent of the steady-state value of the dust coma. transient events are detected by studying the brightness slope of the outburst plume with continuous streams of outflowing gas and dust triggered by driving mechanisms, as yet not understood, which remain active for several minutes to less than a few hours. | investigating the physical properties of outbursts on comet 67p/churyumov-gerasimenko |
thermal history of mimas and enceladus is investigated from the beginning of accretion to 400 myr. the numerical model of convection combined with the parameterized theory is used. the following heat sources are included: short lived and long lived radioactive isotopes, accretion, serpentinization, and phase changes. the heat transfer processes are: conduction, solid state convection, and liquid state convection. we find that temperature of mimas' interior was significantly lower than that of enceladus. if mimas accreted 1.8 myr after cai then the internal melting and differentiation did not occur at all. comparison of thermal models of mimas and enceladus indicates that conditions favorable for the start of tidal heating lasted for a short time ( 107 yr) in mimas and for 108 yr in enceladus. this could explain the mimas—enceladus paradox. in fact, in view of the chronology based on cometary impact rate, one cannot discard a possibility that also mimas was for some time active and it has the interior differentiated on porous core and icy mantle. | comparison of early evolutions of mimas and enceladus |
periodic comets move around the sun on elliptical orbits. as such comet 67p/churyumov-gerasimenko (hereafter 67p) spends a portion of time in the inner solar system where it is exposed to increased solar insolation. therefore given the change in heliocentric distance, in case of 67p from aphelion at 5.68 au to perihelion at ~1.24 au, the comet's activity—the production of neutral gas and dust—undergoes significant variations. as a consequence, during the inbound portion, the mass loading of the solar wind increases and extends to larger spatial scales. this paper investigates how this interaction changes the character of the plasma environment of the comet by means of multifluid mhd simulations. the multifluid mhd model is capable of separating the dynamics of the solar wind ions and the pick-up ions created through photoionization and electron impact ionization in the coma of the comet. we show how two of the major boundaries, the bow shock and the diamagnetic cavity, form and develop as the comet moves through the inner solar system. likewise for 67p, although most likely shifted back in time with respect to perihelion passage, this process is reversed on the outbound portion of the orbit. the presented model herein is able to reproduce some of the key features previously only accessible to particle-based models that take full account of the ions' gyration. the results shown herein are in decent agreement to these hybrid-type kinetic simulations. | modeled interaction of comet 67p/churyumov-gerasimenko with the solar wind inside 2 au |
the stardust spacecraft was the first mission to return solid samples from a body beyond the moon. as the fourth nasa discovery mission, it retrieved samples from the comet 81p/wild 2, that is believed to have formed at the outer fringe of the solar nebula. the return of these samples provides unprecedented opportunities to compare astronomical (remote sensing) and sample analysis (ground truth) information for a known primitive solar system body. the samples make it possible to compare materials from the outer solar system with sample-derived and astronomical data for asteroids, the parents of most meteorites, which formed much closer to the sun. the samples returned by stardust are the first primitive collected materials from a known body, and as such they provide contextual insight for all primitive meteoritic samples. | chapter 4 - the stardust sample return mission |
we report high-precision secondary ion mass spectrometer triple oxygen isotope systematics (95 individual analyses) from 37 micrometeorites (mms) collected from south pole water well (spww), antarctica. the study population focuses on unmelted coarse-grained (cg) mms (n = 23) with both multiple (n = 14) and single-mineral (n = 9) varieties investigated. we also analysed relict minerals in porphyritic cosmic spherules (n = 13) and the relict matrix in a single scoriaceous fine-grained (fg) mm. the target minerals investigated are primarily olivine (fo ∼ 43-99%) and spinel. textural, chemical and isotopic data confirm that both olivine and spinel grains have retained their pre-atmospheric o-isotope compositions, allowing inferences to be drawn about their formation and parent body affinities. we separate the study population into three groups: spinel-free particles (consisting of the cgmms and po cosmic spherules), spinel-bearing mms and the single fgmm. olivine grains in spinel-free mms vary between δ17o: -12.6‰ and +3.5‰, δ18o: -9.6‰ and +7.5‰, and δ17o: -9.5‰ and +1.3‰ and define a slope-1 profile in δ18o-δ17o isotope space. they are most likely fragmented chondrules, with both type i and type ii varieties represented. their observed mg#-δ17o distribution is best explained by a mixture of cm chondrules and either cr chondrules, tagish lake chondrules or wild2 cometary silicates. one of these chondrule-like mms has an isotopically heterogeneous composition, characterised by a single olivine grain with a markedly 16o-rich composition (δ17o: -16.3‰), suggesting it is a relict silicate fragment of aoa material that was incorporated into the chondrule precursor. we analysed 11 spinel grains in five spinel-bearing mms. in all instances spinels are nearly pure mgal2o4 with isotopically light (16o-rich) compositions (ranging from δ17o: -34.4‰ to -0.9‰, δ18o: -30.8‰ to +11.0‰, and δ17o: -18.3‰ to -4.4‰). they are therefore 16o-poor relative to spinel found in unaltered cais, indicating a different origin. grains with high cr2o3 contents (>0.5 wt.%) are interpreted originating from al-rich chondrule precursors, while low cr2o3 spinels (<0.5 wt.%) are interpreted as cai-derived material affected by parent body aqueous alteration. finally, we report a single fgmm with a 16o-poor composition (δ17o > 0‰ and δ18o > +15.0‰). this particle adds to our growing inventory of water-rich c-type asteroid samples united by their formation history which is characterised by accretion of abundant heavy water. our work strongly supports findings from earlier in-situ o-isotope studies, concluding that small mms overwhelmingly sample material from cc parent bodies and that cgmms largely sample chondrules and, to a lesser extent, cai material. the analysis of cgmms therefore provides insights into the primitive o-isotope reservoirs that were present in the early solar system and how they interacted. | in-situ o-isotope analysis of relict spinel and forsterite in small (<200 μm) antarctic micrometeorites - samples of chondrules & cais from carbonaceous chondrites |
context. gaia data release 2 (gaia dr2) contains results for 1693 million sources in the magnitude range 3 to 21 based on observations collected by the european space agency gaia satellite during the first 22 months of its operational phase.aims: we describe the input data, models, and processing used for the astrometric content of gaia dr2, and the validation of these resultsperformed within the astrometry task.methods: some 320 billion centroid positions from the pre-processed astrometric ccd observations were used to estimate the five astrometric parameters (positions, parallaxes, and proper motions) for 1332 million sources, and approximate positions at the reference epoch j2015.5 for an additional 361 million mostly faint sources. these data were calculated in two steps. first, the satellite attitude and the astrometric calibration parameters of the ccds were obtained in an astrometric global iterative solution for 16 million selected sources, using about 1% of the input data. this primary solution was tied to the extragalactic international celestial reference system (icrs) by means of quasars. the resulting attitude and calibration were then used to calculate the astrometric parameters of all the sources. special validation solutions were used to characterise the random and systematic errors in parallax and proper motion.results: for the sources with five-parameter astrometric solutions, the median uncertainty in parallax and position at the reference epoch j2015.5 is about 0.04 mas for bright (g < 14 mag) sources, 0.1 mas at g = 17 mag, and 0.7 masat g = 20 mag. in the proper motion components the corresponding uncertainties are 0.05, 0.2, and 1.2 mas yr-1, respectively.the optical reference frame defined by gaia dr2 is aligned with icrs and is non-rotating with respect to the quasars to within 0.15 mas yr-1. from the quasars and validation solutions we estimate that systematics in the parallaxes depending on position, magnitude, and colour are generally below 0.1 mas, but the parallaxes are on the whole too small by about 0.03 mas. significant spatial correlations of up to 0.04 mas in parallax and 0.07 mas yr-1 in proper motion are seen on small (< 1 deg) and intermediate (20 deg) angular scales. important statistics and information for the users of the gaia dr2 astrometry are given in the appendices. | gaia data release 2. the astrometric solution |
context. gaia early data release 3 (gaia edr3) contains results for 1.812 billion sources in the magnitude range g = 3-21 based on observations collected by the european space agency gaia satellite during the first 34 months of its operational phase.aims: we describe the input data, the models, and the processing used for the astrometric content of gaia edr3, as well as the validation of these results performed within the astrometry task.methods: the processing broadly followed the same procedures as for gaia dr2, but with significant improvements to the modelling of observations. for the first time in the gaia data processing, colour-dependent calibrations of the line- and point-spread functions have been used for sources with well-determined colours from dr2. in the astrometric processing these sources obtained five-parameter solutions, whereas other sources were processed using a special calibration that allowed a pseudocolour to be estimated as the sixth astrometric parameter. compared with dr2, the astrometric calibration models have been extended, and the spin-related distortion model includes a self-consistent determination of basic-angle variations, improving the global parallax zero point.results: gaia edr3 gives full astrometric data (positions at epoch j2016.0, parallaxes, and proper motions) for 1.468 billion sources (585 millionwith five-parameter solutions, 882 million with six parameters), and mean positions at j2016.0 for an additional 344 million.solutions with five parameters are generally more accurate than six-parameter solutions, and are available for 93% of the sources brighter than the 17th magnitude. the median uncertainty in parallax and annual proper motion is 0.02-0.03 mas at magnitude g = 9-14, and around 0.5 mas at g = 20. extensive characterisation of the statistical properties of the solutions is provided, including the estimated angular power spectrum of parallax bias from the quasars. | gaia early data release 3. the astrometric solution |
context. the erosita x-ray telescope on board the spectrum-poentgen-gamma (spg) observatory combines a large field of view and a large collecting area in the energy range between ~0.2 and ~8.0 kev. this gives the telescope the capability to perform uniform scanning observations of large sky areas.aims: srg/erosita performed scanning observations of the ~140 square degree erosita final equatorial depth survey field (the efeds field) as part of its performance verification phase ahead of the planned four year of all-sky scanning operations. the observing time of efeds was chosen to slightly exceed the depth expected in an equatorial field after the completion of the all-sky survey. while verifying the capability of erosita to perform large-area uniform surveys and saving as a test and training dataset to establish calibration and data analysis procedures, the efeds survey also constitutes the largest contiguous soft x-ray survey at this depth to date, supporting a range of early erosita survey science investigations. here we (i) present a catalogue of detected x-ray sources in the efeds field providing information about source positions and extent, as well as fluxes in multiple energy bands, and (ii) document the suite of tools and procedures developed for erosita data processing and analysis, which were validated and optimised by the efeds work.methods: the data were fed through a standard data processing pipeline, which appltes x-ray event calibration and provides a set of standard calibrated data products. a mutiti-stage source detection procedure, building in part on experience from xmm-newton, was optimised and calibrated by performing realistic simulations of the erosita efeds observations. source fluxes were computed in multiple standard energy bands by forced point source fitting and aperture photometry. we cross-matched the erosita efeds source catalogue with previous xmm-atlas observations, which confirmed the excellentt agreement of the erosita and xmm-atlas source fluxes. astrometric corrections were performed by cross-matching the erosita source positions with an optical reference catalogue of quasars.results: we present a primary catalogue of 27 910 x-ray sources (542 of which are significantly spatially extended) detected in the 0.2-2.3 kev energy range with detection likelihoods ≥6, corresponding to a (point source) flux limit of 6.5 × 10-15 erg cm-2 s-1 in the 0.5-2.0 kev energy band (80% completeness). a supplementary catalogue contains 4774 low-significance source candidates with detection likelihoods between 5 and 6. in addition, a hard-band sample of 246 sources detected in the energy range 22.3-5.0 kev above a detection likelihood of 10 is provided. in an appendix, we finally describe the dedicated data analysis software package, the erosita calibration database, and the standard calibrated data products. the catalogues are available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/661/a1 | the erosita final equatorial depth survey (efeds). x-ray catalogue |
trotterization-based, iterative approaches to quantum simulation (qs) are restricted to simulation times less than the coherence time of the quantum computer (qc), which limits their utility in the near term. here, we present a hybrid quantum-classical algorithm, called variational fast forwarding (vff), for decreasing the quantum circuit depth of qss. vff seeks an approximate diagonalization of a short-time simulation to enable longer-time simulations using a constant number of gates. our error analysis provides two results: (1) the simulation error of vff scales at worst linearly in the fast-forwarded simulation time, and (2) our cost function's operational meaning as an upper bound on average-case simulation error provides a natural termination condition for vff. we implement vff for the hubbard, ising, and heisenberg models on a simulator. in addition, we implement vff on rigetti's qc to demonstrate simulation beyond the coherence time. finally, we show how to estimate energy eigenvalues using vff. | variational fast forwarding for quantum simulation beyond the coherence time |
emerging high-redshift cosmological probes, in particular quasars (qsos), show a preference for larger matter densities, ωm≈1 , within the flat λ cdm framework. here, using the risaliti-lusso relation for standardizable qsos, we demonstrate that the qsos recover the same planck-λ cdm universe as type ia supernovae (sn), ωm≈0.3 at lower redshifts 0 <z ≲0.7 , before transitioning to an einstein-de sitter universe (ωm=1 ) at higher redshifts z ≳1 . we illustrate the same trend, namely increasing ωm and decreasing h0 with redshift, in sn but poor statistics prevent a definitive statement. we explain physically why the trend may be expected and show the intrinsic bias through non-gaussian tails with mock sn data. our results highlight an intrinsic bias in the flat λ cdm universe, whereby ωm increases, h0 decreases and s8 increases with effective redshift, thus providing a new perspective on λ cdm tensions; even in a planck-λ cdm universe the current tensions may be expected. | revealing intrinsic flat λ cdm biases with standardizable candles |
in the past few years wide-field optical and uv transient surveys and x-ray telescopes have allowed us to identify a few dozen candidate tidal disruption events (tdes). while in theory the physical processes in tdes are ubiquitous, a few distinct classes of tdes have been observed. some tdes radiate mainly in nuv/optical, while others produce prominent x-rays. moreover, relativistic jets have been observed in only a handful of tdes. this diversity might be related to the details of the super-eddington accretion and emission physics relevant to tde disks. in this letter, we utilize novel three-dimensional general relativistic radiation magnetohydrodynamics simulations to study the super-eddington compact disk phase expected in tdes. consistent with previous studies, geometrically thick disks, wide-angle optically thick fast outflows, and relativistic jets are produced. the outflow density and velocity depend sensitively on the inclination angle, and hence so does the reprocessing of emission produced from the inner disk. we then use monte carlo radiative transfer to calculate the reprocessed spectra and find that that the observed ratio of optical to x-ray fluxes increases with increasing inclination angle. this naturally leads to a unified model for different classes of tdes in which the spectral properties of the tde depend mainly on the viewing angle of the observer with respect to the orientation of the disk. | a unified model for tidal disruption events |
we use global three-dimensional radiation magnetohydrodynamical simulations to study accretion disks onto a 5× {10}8{m}⊙black hole with accretion rates varying from ∼ 250{l}edd}/{c}2 to 520{l}edd}/{c}2. we initialize the disks with a weakly magnetized torus centered at either 50 or 80 gravitational radii, leading to self-consistent turbulence generated by the magnetorotational instability (mri). the inner regions of all disks have radiation pressure ∼104-106 times the gas pressure. nonaxisymmetric density waves that steepen into spiral shocks form as gas flows toward the black hole. maxwell stress from mri turbulence can be larger than the reynolds stress only when the net vertical magnetic flux is sufficiently large. outflows are formed with a speed of ∼0.1-0.4c. when the accretion rate is smaller than ∼ 500{l}edd}/{c}2, outflows are launched from ∼10 gravitational radii, and the radiative efficiency is ∼5%-7%. for an accretion rate reaching 1500{l}edd}/{c}2, most of the funnel region near the rotation axis becomes optically thick, and the outflow is launched from beyond 50 gravitational radii. the radiative efficiency is reduced to 1%. we always find that the kinetic energy luminosity associated with the outflow is at most ∼15%-30% of the radiative luminosity. the mass flux in the outflow is ∼15%-50% of the net mass accretion rates. we discuss the implications of our simulation results on the observational properties of these disks. | super-eddington accretion disks around supermassive black holes |
we present a measurement of baryon acoustic oscillations (bao) in the cross-correlation of quasars with the lyα-forest flux transmission at a mean redshift of z = 2.40. the measurement uses the complete sloan digital sky survey (sdss-iii) data sample: 168 889 forests and 234 367 quasars from the sdss data release dr12. in addition to the statistical improvement on our previous study using dr11, we have implemented numerous improvements at the analysis level enabling a more accurate measurement of this cross-correlation. we have also developed the first simulations of the cross-correlation that allow us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the bao peak position. we measure the two ratios dh(z = 2.40) /rd = 9.01 ± 0.36 and dm(z = 2.40) /rd = 35.7 ± 1.7, where the errors include marginalization over the non-linear velocity of quasars and the cross-correlation of metals and quasars, among other effects. these results are within 1.8σ of the prediction of the flat-λcdm model describing the observed cosmic microwave background anisotropies. we combine this study with the lyα-forest auto-correlation function, yielding dh(z = 2.40) /rd = 8.94 ± 0.22 and dm(z = 2.40) /rd = 36.6 ± 1.2, within 2.3σ of the same flat-λcdm model. | baryon acoustic oscillations from the complete sdss-iii lyα-quasar cross-correlation function at z = 2.4 |
we find that clouds of optically thin, pressure-confined gas are prone to fragmentation as they cool below ∼106 k. this fragmentation follows the lengthscale ∼cstcool, ultimately reaching very small scales (∼0.1 pc/n), as they reach the temperature ∼104 k at which hydrogen recombines. while this lengthscale depends on the ambient pressure confining the clouds, we find that the column density through an individual fragment ncloudlet ∼ 1017 cm-2 is essentially independent of environment; this column density represents a characteristic scale for atomic gas at 104 k. we therefore suggest that 'clouds' of cold, atomic gas may, in fact, have the structure of a mist or a fog, composed of tiny fragments dispersed throughout the ambient medium. we show that this scale emerges in hydrodynamic simulations, and that the corresponding increase in the surface area may imply rapid entrainment of cold gas. we also apply it to a number of observational puzzles, including the large covering fraction of diffuse gas in galaxy haloes, the broad-line widths seen in quasar and agn spectra and the entrainment of cold gas in galactic winds. while our simulations make a number of assumptions and thus have associated uncertainties, we show that this characteristic scale is consistent with a number of observations, across a wide range of astrophysical environments. we discuss future steps for testing, improving and extending our model. | a characteristic scale for cold gas |
traditional cosmological hydrodynamics simulations fail to spatially resolve the circumgalactic medium (cgm), the reservoir of tenuous gas surrounding a galaxy and extending to its virial radius. we introduce the technique of enhanced halo resolution (ehr), enabling more realistic physical modeling of the simulated cgm by consistently forcing gas refinement to smaller scales throughout the virial halo of a simulated galaxy. we investigate the effects of ehr in the tempest simulations, a suite of enzo-based cosmological zoom simulations following the evolution of an l* galaxy, resolving spatial scales of 500 comoving pc out to 100 comoving kpc in galactocentric radius. among its many effects, ehr (1) changes the thermal balance of the cgm, increasing its cool gas content and decreasing its warm/hot gas content; (2) preserves cool gas structures for longer periods; and (3) enables these cool clouds to exist at progressively smaller size scales. observationally, this results in a boost in “low ions” like h i and a drop in “high ions” like o vi throughout the cgm. these effects of ehr do not converge in the tempest simulations, but extrapolating these trends suggests that the cgm is actually a mist consisting of ubiquitous, small, long-lived, cool clouds suspended in a medium at the halo virial temperature. we find that ehr produces the above effects by (1) better sampling the distribution of cgm phases, enabling runaway cooling in the dense, cool tail of the phase distribution; and (2) preventing cool gas clouds from artificially mixing with the ambient hot halo and evaporating. | the impact of enhanced halo resolution on the simulated circumgalactic medium |
recently it has been shown that the cosmological dynamics of covariant f(q) gravity depend on different affine connections. in this paper, two specific f(q) models are investigated with sne+cc+bao+qso observational data, and the spatial curvature of the universe is studied in covariant f(q) gravity. it is found that the parameters x0 and x0' characterizing affine connections significantly affect the behavior of the effective equation of state wq and may drive it across the phantom divide line. these results imply some inertial effects of the universe change the cosmic dynamics. however based on the bayesian evidence, the zero inertial effect is more favored in the flat universe. moreover, a closed universe is favored not only in the λ cdm model but also in covariant f(q) gravity. the f(q) models have less support evidence than the λ cdm model in the non-flat universe. | cosmological constraints in covariant f(q) gravity with different connections |
if a significant fraction of the dark matter in the universe is made of an ultra-light scalar field, named fuzzy dark matter (fdm) with a mass ma of the order of 10-22 - 10-21 ev, then its de broglie wavelength is large enough to impact the physics of large-scale structure formation. in particular, the associated cut-off in the linear matter power spectrum modifies the structure of the intergalactic medium (igm) at the scales probed by the lyman-α forest of distant quasars. we study this effect by making use of dedicated cosmological simulations which take into account the hydrodynamics of the igm. we explore heuristically the amplitude of quantum pressure for the fdm masses considered here and conclude that quantum effects should not modify significantly the non-linear evolution of matter density at the scales relevant to the measured lyman-α flux power, and for ma ≳ 10 - 22 ev. we derive a scaling law between ma and the mass of the well-studied thermal warm dark matter model that is best adapted to the lyman-α forest data, and differs significantly from the one inferred by a simple linear extrapolation. by comparing fdm simulations with the lyman-α flux power spectra determined from the boss survey, and marginalizing over relevant nuisance parameters, we exclude fdm masses in the range 10 - 22 ≲ ma < 2.3 × 10 - 21 ev at 95 per cent cl. adding higher resolution lyman-α spectra extends the exclusion range up to 2.9 × 10-21 ev. this provides a significant constraint on fdm models tailored to solve the `small-scale problems' of λcdm. | constraining the mass of light bosonic dark matter using sdss lyman-α forest |
this is the third paper in a series aimed at finding reionization-era quasars with the combination of desi legacy imaging surveys (dels), the pan-starrs1 (ps1) survey, and near-infrared imaging surveys, such as the ukirt hemisphere survey (uhs), as well as the wide-field infrared survey explorer (wise) mid-infrared survey. in this paper, we describe the updated quasar candidate selection procedure, report the discovery of 16 quasars at 6.4 ≲ z ≲ 6.9 from an area of ∼13,020 deg2, and present the quasar luminosity function (qlf) at z ∼ 6.7. the measured qlf follows {{φ }}({l}1450)\propto {l}1450-2.35 in the magnitude range -27.6 < m 1450 < -25.5. we determine the quasar comoving spatial density at < z> = 6.7 and m 1450 < -26.0 to be 0.39 ± 0.11 gpc-3 and find the exponential density evolution parameter to be k = -0.78 ± 0.18 from z ∼ 6 to z ∼ 6.7, corresponding to a rapid decline by a factor of ∼6 per unit redshift toward earlier epochs. this indicates that the rapid decline of quasar spatial density at z > 5 that was found by previous works continues to z > 6, at a rate significantly faster than the average decline rate between z ∼ 3 and 5. we measured quasar comoving emissivity at z ∼ 6.7, which indicates that high-redshift quasars are highly unlikely to make a significant contribution to hydrogen reionization. the broad absorption line quasar fraction at z ≳ 6.5 is measured to be ≳22%. in addition, we also report the discovery of six additional quasars at z ∼ 6 in the appendix. | exploring reionization-era quasars. iii. discovery of 16 quasars at 6.4 ≲ z ≲ 6.9 with desi legacy imaging surveys and the ukirt hemisphere survey and quasar luminosity function at z ∼ 6.7 |
we present an observational constraint for the typical active galactic nucleus (agn) phase lifetime. the argument is based on the time lag between an agn central engine switching on and becoming visible in x-rays, and the time the agn then requires to photoionize a large fraction of the host galaxy. based on the typical light travel time across massive galaxies, and the observed fraction of x-ray-selected agn without agn-photoionized narrow lines, we estimate that the agn phase typically lasts ∼105 yr. this lifetime is short compared to the total growth time of 107-109 yr estimated from e.g. the soltan argument and implies that black holes grow via many such short bursts and that agn therefore `flicker' on and off. we discuss some consequences of this flickering behaviour for agn feedback and the analogy of x-ray binaries and agn lifecycles. | active galactic nuclei flicker: an observational estimate of the duration of black hole growth phases of ∼105 yr |
we present a new catalogue of ∼2400 optically selected quasars with spectroscopic redshifts and x-ray observations from either chandra or xmm-newton. the sample can be used to investigate the non-linear relation between the ultraviolet (uv) and x-ray luminosity of quasars as well as to build a hubble diagram up to a redshift of z ∼ 7.5. we selected sources that are neither reddened by dust in the optical and uv nor obscured by gas in the x-rays, and whose x-ray fluxes are free from flux-limit-related biases. after checking for any possible systematics, we confirm, in agreement with our previous works, that the x-ray to uv relation provides distance estimates matching those from supernovae up to z ∼ 1.5, and its slope shows no redshift evolution up to z ∼ 5. we provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the hubble diagram of quasars is well reproduced by the standard flat cold dark matter model up to z ∼ 1.5-2, but strong deviations emerge at higher redshifts. since we have minimised all non-negligible systematic effects and proven the stability of the lx - luv relation at high redshifts, we conclude that an evolution of the expansion rate of the universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars. full table 3 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/642/a150 | quasars as standard candles. iii. validation of a new sample for cosmological studies |
the quest for binary and dual supermassive black holes (smbhs) at the dawn of the multi-messenger era is compelling. detecting dual active galactic nuclei (agn) - active smbhs at projected separations larger than several parsecs - and binary agn - probing the scale where smbhs are bound in a keplerian binary - is an observational challenge. the study of agn pairs (either dual or binary) also represents an overarching theoretical problem in cosmology and astrophysics. the agn triggering calls for detailed knowledge of the hydrodynamical conditions of gas in the imminent surroundings of the smbhs and, at the same time, their duality calls for detailed knowledge on how galaxies assemble through major and minor mergers and grow fed by matter along the filaments of the cosmic web. this review describes the techniques used across the electromagnetic spectrum to detect dual and binary agn candidates and proposes new avenues for their search. the current observational status is compared with the state-of-the-art numerical simulations and models for formation of dual and binary agn. binary smbhs are among the loudest sources of gravitational waves (gws) in the universe. the search for a background of gws at nhz frequencies from inspiralling smbhs at low redshifts, and the direct detection of signals from their coalescence by the laser interferometer space antenna in the next decade, make this a theme of major interest for multi-messenger astrophysics. this review discusses the future facilities and observational strategies that are likely to significantly advance this fascinating field. | the quest for dual and binary supermassive black holes: a multi-messenger view |
a 10% difference in the scale for the hubble parameter constitutes a clear problem for cosmology. here, considering angular distribution of type ia supernovae (sn) within the pantheon compilation and working within flat λ cdm cosmology, we observe a correlation between higher h0 and the cmb dipole direction, confirming our previous results for strongly lensed quasars [classical quantum gravity 38, 184001 (2021), 10.1088/1361-6382/ac1a81]. concretely, we record a ∼1 km /s /mpc variation in h0 at antipodal points on the sky within the pantheon sample, which is evident in the low z subsample (z ≲0.075 ) and gets enhanced by higher redshift sn. our work raises the possibility that we may be at the precision required to probe anisotropic hubble expansions, while providing a concrete prediction for future inferences of h0. | hints of flrw breakdown from supernovae |
we present results from a parsec-scale jet kinematics study of 409 bright radio-loud active galactic nuclei (agns) based on 15 ghz very long baseline array (vlba) data obtained between 1994 august 31 and 2016 december 26 as part of the 2 cm vlba survey and monitoring of jets in active galactic nuclei with vlba experiments (mojave) programs. we tracked 1744 individual bright features in 382 jets over at least 5 epochs. a majority (59%) of the best-sampled jet features showed evidence of accelerated motion at the >3σ level. although most features within a jet typically have speeds within ∼40% of a characteristic median value, we identified 55 features in 42 jets that had unusually slow pattern speeds, nearly all of which lie within 4 pc (100 pc deprojected) of the core feature. our results, combined with other speeds from the literature, indicate a strong correlation between apparent jet speed and synchrotron peak frequency, with the highest jet speeds being found only in low-peaked agns. using monte carlo simulations, we find best-fit parent population parameters for a complete sample of 174 quasars above 1.5 jy at 15 ghz. acceptable fits are found with a jet population that has a simple unbeamed power-law luminosity function incorporating pure luminosity evolution and a power-law lorentz factor distribution ranging from 1.25 to 50 with slope -1.4 ± 0.2. the parent jets of the brightest radio quasars have a space density of 261 ± 19 gpc-3 and unbeamed 15 ghz luminosities above ∼1024.5 w hz-1, consistent with fr ii class radio galaxies. | mojave. xvii. jet kinematics and parent population properties of relativistically beamed radio-loud blazars |
emerging high redshift cosmological probes, in particular quasars (qsos), show a preference for larger matter densities, $\omega_{m} \approx 1$, within the flat $\lambda$cdm framework. here, using the risaliti-lusso relation for standardizable qsos, we demonstrate that the qsos recover the \textit{same} planck-$\lambda$cdm universe as type ia supernovae (sn), $\omega_m \approx 0.3$ at lower redshifts $ 0 < z \lesssim 0.7$, before transitioning to an einstein-de sitter universe ($\omega_m =1$) at higher redshifts $z \gtrsim 1$. we illustrate the same trend, namely increasing $\omega_{m}$ and decreasing $h_0$ with redshift, in sn but poor statistics prevent a definitive statement. we explain physically why the trend is expected in the flat $\lambda$cdm cosmology, illustrate the intrinsic bias and non-gaussian tails with mock pantheon data, and identify a similar trend in bao below $z=1$. our results highlight an intrinsic bias in the flat $\lambda$cdm universe, whereby $\omega_m$ increases, $h_0$ decreases and $s_8$ increases with effective redshift, thus providing a new perspective on $\lambda$cdm tensions; even in a planck-$\lambda$cdm universe the current tensions might have been expected. | revealing intrinsic flat $\\lambda$cdm biases with standardizable candles |
luminous z ≥ 7 quasars provide direct probes of the evolution of supermassive black holes (smbhs) and the intergalactic medium (igm) during the epoch of reionization (eor). the lyα damping wing absorption imprinted by neutral hydrogen in the igm can be detected in a single eor quasar spectrum, allowing the measurement of the igm neutral fraction toward that line of sight. however, damping wing features have only been detected in two z > 7 quasars in previous studies. in this paper, we present new high-quality optical and near-infrared spectroscopy of the z = 7.00 quasar des j025216.64-050331.8 obtained with keck/near-infrared echellette spectrometer and gemini/gmos. by using the mg ii single-epoch virial method, we find that it hosts a $(1.39\pm 0.16)\times {10}^{9}\,{m}_{\odot }$ smbh accreting at an eddington ratio of λedd = 0.7 ± 0.1, consistent with the values seen in other luminous z ∼ 7 quasars. furthermore, the lyα region of the spectrum exhibits a strong damping wing absorption feature. the lack of associated metal absorption in the quasar spectrum indicates that this absorption is imprinted by a neutral igm. using a state-of-the-art model developed by davies et al., we measure a volume-averaged neutral hydrogen fraction at z = 7 of $\langle {x}_{{\rm{h}}{\rm{i}}}\rangle ={0.70}_{-0.23}^{+0.20}{(}_{-0.48}^{+0.28})$ within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of ${10}^{3}\leqslant {t}_{{\rm{q}}}\leqslant {10}^{8}\,\mathrm{yr}$ . this is the highest igm neutral fraction yet measured using reionization-era quasar spectra. | a significantly neutral intergalactic medium around the luminous z = 7 quasar j0252-0503 |
this study introduces novel constraints on the free-streaming of thermal relic warm dark matter (wdm) from lyman-$\alpha$ forest flux power spectra. our analysis utilises a high-resolution, high-redshift sample of quasar spectra observed using the hires and uves spectrographs ($z=4.2-5.0$). we employ a bayesian inference framework and a simulation-based likelihood that encompasses various parameters including the free-streaming of dark matter, cosmological parameters, the thermal history of the intergalactic medium, and inhomogeneous reionization, to establish lower limits on the mass of a thermal relic wdm particle of $5.7\;\mathrm{kev}$ (at 95\% c.l.). this result surpasses previous limits from the lyman-$\alpha$ forest through reduction of the measured uncertainties due to a larger statistical sample and by measuring clustering to smaller scales ($k_{\rm max}=0.2\;\mathrm{km^{-1}\,s}$). the approximately two-fold improvement due to the expanded statistical sample suggests that the effectiveness of lyman-$\alpha$ forest constraints on wdm models at high redshifts are limited by the availability of high-quality quasar spectra. restricting the analysis to comparable scales and thermal history priors as in prior studies ($k_{\rm max}<0.1\;\mathrm{km^{-1}\,s}$) lowers the bound on the wdm mass to $4.1\;\mathrm{kev}$. as the precision of the measurements increases, it becomes crucial to examine the instrumental and modelling systematics. on the modelling front, we argue that the impact of the thermal history uncertainty on the wdm particle mass constraint has diminished due to improved independent observations. at the smallest scales, the primary source of modeling systematic arises from the structure in the peculiar velocity of the intergalactic medium and inhomogeneous reionization. | unveiling dark matter free-streaming at the smallest scales with high redshift lyman-alpha forest |
we develop a new method, which is based on the optimal redshift weighting scheme, to extract the maximal tomographic information of baryonic acoustic oscillations (bao) and redshift space distortions (rsd) from the extended baryon oscillation spectroscopic survey (eboss) data release 14 quasar (dr14q) survey. we validate our method using the extended zel'dovich mocks, and apply our pipeline to the eboss dr14q sample in the redshift range of 0.8 < z < 2.2. we report a joint measurement of fσ8 and two-dimensional bao parameters da and h at four effective redshifts of zeff = 0.98, 1.23, 1.52, and 1.94, and provide the full data covariance matrix. using our measurement combined with boss dr12, main galaxy sample (mgs), and 6 degree field galaxy survey (6dfgs) bao measurements, we find that the existence of dark energy is supported by observations at a 7.4σ significance level. combining our measurement with boss dr12 and planck observations, we constrain the gravitational growth index to be γ = 0.580 ± 0.082, which is fully consistent with the prediction of general relativity. this paper is part of a set that analyses the eboss dr14 quasar sample. | the clustering of the sdss-iv extended baryon oscillation spectroscopic survey dr14 quasar sample: a tomographic measurement of cosmic structure growth and expansion rate based on optimal redshift weights |
we describe the spectroscopic data processing pipeline of the dark energy spectroscopic instrument (desi), which is conducting a redshift survey of about 40 million galaxies and quasars using a purpose-built instrument on the 4 m mayall telescope at kitt peak national observatory. the main goal of desi is to measure with unprecedented precision the expansion history of the universe with the baryon acoustic oscillation technique and the growth rate of structure with redshift space distortions. ten spectrographs with three cameras each disperse the light from 5000 fibers onto 30 ccds, covering the near-uv to near-infrared (3600-9800 å) with a spectral resolution ranging from 2000 to 5000. the desi data pipeline generates wavelength- and flux-calibrated spectra of all the targets, along with spectroscopic classifications and redshift measurements. fully processed data from each night are typically available to the desi collaboration the following morning. we give details about the pipeline's algorithms, and provide performance results on the stability of the optics, the quality of the sky background subtraction, and the precision and accuracy of the instrumental calibration. this pipeline has been used to process the desi survey validation data set, and has exceeded the project's requirements for redshift performance, with high efficiency and a purity greater than 99% for all target classes. | the spectroscopic data processing pipeline for the dark energy spectroscopic instrument |
we present the final data from the sloan digital sky survey reverberation mapping (sdss-rm) project, a precursor to the sdss-v black hole mapper reverberation mapping program. this data set includes 11-year photometric and 7-year spectroscopic light curves for 849 broad-line quasars over a redshift range of 0.1<z<4.5 and a luminosity range of lbol=1e44-47.5 erg/s, along with spectral and variability measurements. we report 23, 81, 125, and 110 reverberation mapping lags (relative to optical continuum variability) for broad halpha, hbeta, mgii and civ using the sdss-rm sample, spanning much of the luminosity and redshift ranges of the sample. using 30 low-redshift rm agns with dynamical-modeling black hole masses, we derive a new estimate of the average virial factor of <log f>=0.62+-0.07 for the line dispersion measured from the rms spectrum. the intrinsic scatter of individual virial factors is 0.31+-0.07 dex, indicating a factor of two systematic uncertainty in rm black hole masses. our lag measurements reveal significant r-l relations for hbeta and mgii at high redshift, consistent with the latest measurements based on heterogeneous samples. while we are unable to robustly constrain the slope of the r-l relation for civ given the limited dynamical range in luminosity, we found substantially larger scatter in civ lags at fixed l1350. using the sdss-rm lag sample, we derive improved single-epoch (se) mass recipes for hbeta, mgii and civ, which are consistent with their respective rm masses as well as between the se recipes from two different lines, over the luminosity range probed by our sample. the new hbeta and mgii recipes are approximately unbiased estimators at given rm masses, but there are systematic biases in the civ recipe. the intrinsic scatter of se masses around rm masses is ~0.45 dex for hbeta and mgii, increasing to ~0.58 dex for civ. | the sloan digital sky survey reverberation mapping project: key results |
the flux power spectrum (fps) of the high-resolution lyman-α forest data exhibits suppression at small scales. the origin of this suppression can be due to long-sought warm dark matter (wdm) or to thermal effects, related to the largely unknown reionization history of the universe. previous works explored a specific class of reionization histories that exhibit sufficiently strong thermal suppression and leave little room for wdm interpretation. in this work, we choose a different class of reionization histories, fully compatible with available data on evolution of reionization, but much colder than the reionization histories used by previous authors in determining the nature of dark matter, thus leaving the broadest room for the wdm interpretation of the suppression in the fps. we find that wdm thermal relics with masses below 1.9 kev (95 per cent cl) would produce a suppression at scales that are larger than observed maximum of the fps, independently of assumptions about thermal effects. this wdm mass is significantly lower than previously claimed bounds, demonstrating the level of systematic uncertainty of the lyman-α forest method, due to the previous modelling. we also discuss how this uncertainty may affect also data at large scales measured by eboss(baryon oscillation spectroscopic survey). | how to constrain warm dark matter with the lyman-α forest |
we re-analyse high redshift and high resolution lyman-α forest spectra considered in [1], seeking to constrain the properties of warm dark matter particles. compared to this previous work, we consider a wider range of thermal histories of the intergalactic medium. we find that both warm and cold dark matter models can explain the cut-off observed in the flux power spectra of high-resolution observations equally well. this implies, however, very different thermal histories and underlying reionization models. we discuss how to remove this degeneracy. | cutoff in the lyman-α forest power spectrum: warm igm or warm dark matter? |
in this paper, a well‑motivated parameterization of the hubble parameter (h) is revisited that renders two models of dark energy showing some intriguing features of the late‑time accelerating universe. a general quintessence field is considered as a source of dark energy. tighter constraints using recently updated cosmic observational datasets for the considered models have been obtained. the two models described here show a nice fit to the considered uncorrelated hubble datasets, standard candles, gamma ray bursts, quasars, and uncorrelated baryonic acoustic oscillations datasets. using the constrained values of the model parameters, some features of the late‑time accelerating models and obtained the present value of the deceleration parameter (q0), the present value of the hubble parameter (h0) and the transition redshift () from deceleration to acceleration have been discussed. the current value of the deceleration parameter for both models is consistent with the planck 2018 results. the evolution of the geometrical and physical parameters is discussed through graphical representations for both models with some diagnostic analysis. the statistical analysis performed here shows greater results and overall, the outcomes of this investigation are superior to those previously found. | model‑independent study for a quintessence model of dark energy: analysis and observational constraints |
we present measurements of the local primordial non-gaussianity parameter \fnlloc from the clustering of 343,708 quasars with redshifts 0.8 < z < 2.2 distributed over 4808 square degrees from the final data release (dr16) of the extended baryon acoustic oscillation spectroscopic survey (eboss), the largest volume spectroscopic survey up to date. our analysis is performed in fourier space, using the power spectrum monopole at very large scales to constrain the scale dependent halo bias. we carefully assess the impact of systematics on our measurement and test multiple contamination removal methods. we demonstrate the robustness of our analysis pipeline with ez-mock catalogues that simulate the eboss dr16 target selection. we find $f_\mathrm{nl}=-12\pm 21$ (68\% confidence) for the main clustering sample including quasars with redshifts between 0.8 and 2.2, after exploiting a novel neural network scheme for cleaning the dr16 sample and in particular after applying redshift weighting techniques, designed for non-gaussianity measurement from large scales structure, to optimize our analysis, which improve our results by 37\%. | the clustering of galaxies in the completed sdss-iv extended baryon oscillation spectroscopic survey: primordial non-gaussianity in fourier space |
we present a detailed analysis of the point spread function (psf) of jwst nircam imaging in eight filters: f070w, f115w, f150w, f200w, f277w, f356w, f444w, and f480m, using publicly available data. spatial variations in the psf fwhm generally decrease with wavelength: the maximum and rms fractional variations are $\sim20\%$ and $5\%$ in f070w, reduced to $\sim3\%$ and $0.6\%$ in f444w. we compare three commonly-used methods (swarp, photutils, and psfex) to construct model psfs and conclude that psfex delivers the best performance. using simulated images of broad-line agns, we evaluate the impact of psf mismatches on the recoverability of host galaxy properties. host fluxes are generally overestimated when adopting mismatched psf models, with larger overestimation for more agn-dominated systems. broader psfs tend to produce less concentrated hosts while narrower psfs tend to produce more concentrated and compact hosts. systematic uncertainties in host measurements from psf and model mismatches are generally larger than the formal fitting uncertainties for high signal-to-noise ratio data. image decomposition can also lead to an artificial offset between the agn and host centroids, which is common (e.g., $>1\sigma$ [$3\sigma$] detection in $\sim 80%$ [$\sim 20-30\%$] of systems), and scales with the mean host surface brightness. near the surface brightness limit, this artificial offset can reach as large as $\sim80\%$, $26\%$, and $7\%$ of $r_e$ in systems with $r_e=$0.12", 0.48", and 1.92", respectively. we demonstrate our psf construction and image decomposition methods with an example broad-line quasar at $z=1.646$ in the ceers field. | characterization of jwst nircam psfs and implications for agn+host image decomposition |
we analyze new far-ultraviolet spectra of 13 quasars from the z∼ 0.2 cos-halos survey that cover the h i lyman limit of 14 circumgalactic medium (cgm) systems. these data yield precise estimates or more constraining limits than previous cos-halos measurements on the h i column densities {n}{{h}{{i}}}. we then apply a monte-carlo markov chain approach on 32 systems from cos-halos to estimate the metallicity of the cool (t∼ {10}4 k) cgm gas that gives rise to low-ionization state metal lines, under the assumption of photoionization equilibrium with the extragalactic uv background. the principle results are: (1) the cgm of field l* galaxies exhibits a declining h i surface density with impact parameter {r}\perp(at > 99.5 % confidence), (2) the transmission of ionizing radiation through cgm gas alone is 70 ± 7% (3) the metallicity distribution function of the cool cgm is unimodal with a median of {10}-0.51 {z}⊙and a 95% interval ≈ 1/50 {z}⊙to > 3 {z}⊙ ; the incidence of metal-poor (< 1/100 {z}⊙ ) gas is low, implying any such gas discovered along quasar sightlines is typically unrelated to l* galaxies; (4) we find an unexpected increase in gas metallicity with declining {n}{{h}{{i}}} (at > 99.9 % confidence) and, therefore, also with increasing {r}\perp ; the high metallicity at large radii implies early enrichment; and (5) a non-parametric estimate of the cool cgm gas mass is {m}{cgm}{cool}=(9.2+/- 4.3)× {10}10 {m}⊙ , which together with new mass estimates for the hot cgm may resolve the galactic missing baryons problem. future analyses of halo gas should focus on the underlying astrophysics governing the cgm, rather than processes that simply expel the medium from the halo. based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with programs 13033 and 11598. | the cos-halos survey: metallicities in the low-redshift circumgalactic medium |
the recent discovery of a diffuse cosmic neutrino flux extending up to pev energies raises the question of which astrophysical sources generate this signal. blazars are one class of extragalactic sources which may produce such high-energy neutrinos. we present a likelihood analysis searching for cumulative neutrino emission from blazars in the 2nd fermi-lat agn catalog (2lac) using icecube neutrino data set 2009-12, which was optimized for the detection of individual sources. in contrast to those in previous searches with icecube, the populations investigated contain up to hundreds of sources, the largest one being the entire blazar sample in the 2lac catalog. no significant excess is observed, and upper limits for the cumulative flux from these populations are obtained. these constrain the maximum contribution of 2lac blazars to the observed astrophysical neutrino flux to 27% or less between around 10 tev and 2 pev, assuming the equipartition of flavors on earth and a single power-law spectrum with a spectral index of -2.5. we can still exclude the fact that 2lac blazars (and their subpopulations) emit more than 50% of the observed neutrinos up to a spectral index as hard as -2.2 in the same energy range. our result takes into account the fact that the neutrino source count distribution is unknown, and it does not assume strict proportionality of the neutrino flux to the measured 2lac γ-ray signal for each source. additionally, we constrain recent models for neutrino emission by blazars. | the contribution of fermi-2lac blazars to diffuse tev-pev neutrino flux |
we produce 1000 realizations of synthetic clustering catalogues for each type of the tracers used for the baryon acoustic oscillation and redshift space distortion analysis of the sloan digital sky surveys-iv extended baryon oscillation spectroscopic survey final data release (eboss dr16), covering the redshift range from 0.6 to 2.2, to provide reliable estimates of covariance matrices and test the robustness of the analysis pipeline with respect to observational systematics. by extending the zel'dovich approximation density field with an effective tracer bias model calibrated with the clustering measurements from the observational data, we accurately reproduce the two- and three-point clustering statistics of the eboss dr16 tracers, including their cross-correlations in redshift space with very low computational costs. in addition, we include the gravitational evolution of structures and sample selection biases at different redshifts, as well as various photometric and spectroscopic systematic effects. the agreements on the auto-clustering statistics between the data and mocks are generally within $1\, \sigma$ variances inferred from the mocks, for scales down to a few $h^{-1}\, {\rm mpc}$ in configuration space, and up to $0.3\, h\, {\rm mpc}^{-1}$ in fourier space. for the cross correlations between different tracers, the same level of consistency presents in configuration space, while there are only discrepancies in fourier space for scales above $0.15\, h\, {\rm mpc}^{-1}$ . the accurate reproduction of the data clustering statistics permits reliable covariances for multi-tracer analysis. | the completed sdss-iv extended baryon oscillation spectroscopic survey: 1000 multi-tracer mock catalogues with redshift evolution and systematics for galaxies and quasars of the final data release |
direct lyα imaging of intergalactic gas at z∼ 2 has recently revealed giant cosmological structures around quasars, e.g., the slug nebula. despite their high luminosity, the detection rate of such systems in narrow-band and spectroscopic surveys is less than 10%, possibly encoding crucial information on the distribution of gas around quasars and the quasar emission properties. in this study, we use the muse integral-field instrument to perform a blind survey for giant {ly}α nebulae around 17 bright radio-quiet quasars at 3\lt z\lt 4 that does not suffer from most of the limitations of previous surveys. after data reduction and analysis performed with specifically developed tools, we found that each quasar is surrounded by giant {ly}α nebulae with projected sizes larger than 100 physical kiloparsecs and, in some cases, extending up to 320 kpc. the circularly averaged surface brightness profiles of the nebulae appear to be very similar to each other despite their different morphologies and are consistent with power laws with slopes ≈ -1.8. the similarity between the properties of all these nebulae and the slug nebula suggests a similar origin for all systems and that a large fraction of gas around bright quasars could be in a relatively “cold” (t ∼ 104 k) and dense phase. in addition, our results imply that such gas is ubiquitous within at least 50 kpc from bright quasars at 3\lt z\lt 4 independently of the quasar emission opening angle, or extending up to 200 kpc for quasar isotropic emission. based on observations made with eso telescopes at the paranal observatory under programs 094.a-0396, 095.a-0708, 096.a-0345, 094.a-0131, 095.a-0200, and 096.a-0222. | ubiquitous giant lyα nebulae around the brightest quasars at z ∼ 3.5 revealed with muse |
we revisit the blazar sequence exploiting the complete, flux-limited sample of blazars with known redshift detected by the fermi satellite after 4 yr of operations (the 3lac sample). we divide the sources into γ-ray luminosity bins, collect all the archival data for all blazars, and construct their spectral energy distribution (sed). we describe the average sed of blazars in the same luminosity bin through a simple phenomenological function consisting of two broken power laws connecting with a power law describing the radio emission. we do that separately for bl lacs and for flat spectrum radio quasars (fsrqs) and also for all blazars together. the main results are: (i) fsrqs display approximately the same sed as the luminosity increases, but the relative importance of the high-energy peak increases; (ii) as a consequence, the x-ray spectra of fsrqs become harder for larger luminosities; (iii) bl lacs indeed form a sequence: they become redder (i.e. smaller peak frequencies) with increasing luminosities, with a softer γ-ray slope and a larger dominance of the high-energy peak; (iv) for all blazars (bl lacs+fsrqs), these properties become more prominent, as the highest luminosity bin is populated mostly by fsrqs and the lowest luminosity bin mostly by bl lacs. this agrees with the original blazar sequence, although bl lacs never have an average γ-ray slope as hard as found in the original sequence. (v) at high luminosities, a large fraction of fsrqs show signs of thermal emission from the accretion disc, contributing to the optical-uv (ultraviolet). | the fermi blazar sequence |
we present the second realization of the international celestial reference frame (icrf2) at radio wavelengths using nearly 30 years of very long baseline interferometry observations. icrf2 contains precise positions of 3414 compact radio astronomical objects and has a positional noise floor of ∼40 μas and a directional stability of the frame axes of ∼10 μas. a set of 295 new “defining” sources was selected on the basis of positional stability and the lack of extensive intrinsic source structure. the positional stability of these 295 defining sources and their more uniform sky distribution eliminates the two greatest weaknesses of the first realization of the international celestial reference frame (icrf1). alignment of icrf2 with the international celestial reference system was made using 138 positionally stable sources common to both icrf2 and icrf1. the resulting icrf2 was adopted by the international astronomical union as the new fundamental celestial reference frame, replacing icrf1 as of 2010 january 1. | the second realization of the international celestial reference frame by very long baseline interferometry |
context. the kilo-degree survey (kids) is an optical wide-field imaging survey carried out with the vlt survey telescope and the omegacam camera. kids will image 1500 square degrees in four filters (ugri), and together with its near-infrared counterpart viking will produce deep photometry in nine bands. designed for weak lensing shape and photometric redshift measurements, its core science driver is mapping the large-scale matter distribution in the universe back to a redshift of ~0.5. secondary science cases include galaxy evolution, milky way structure, and the detection of high-redshift clusters and quasars.aims: kids is an eso public survey and dedicated to serving the astronomical community with high-quality data products derived from the survey data. public data releases, the first two of which are presented here, are crucial for enabling independent confirmation of the survey's scientific value. the achieved data quality and initial scientific utilization are reviewed in order to validate the survey data.methods: a dedicated pipeline and data management system based on astro-wise, combined with newly developed masking and source classification tools, is used for the production of the data products described here. science projects based on these data products and preliminary results are outlined.results: for 148 survey tiles (≈160 sq.deg.) stacked ugri images have been released, accompanied by weight maps, masks, source lists, and a multi-band source catalogue. limiting magnitudes are typically 24.3, 25.1, 24.9, 23.8 (5σ in a 2'' aperture) in ugri, respectively, and the typical r-band psf size is less than 0.7''. the photometry prior to global homogenization is stable at the ~2% (4%) level in gri (u) with some outliers due to non-photometric conditions, while the astrometry shows a typical 2d rms of 0.03''. early scientific results include the detection of nine high-z qsos, fifteen candidate strong gravitational lenses, high-quality photometric redshifts and structural parameters for hundreds of thousands of galaxies. | the first and second data releases of the kilo-degree survey |
heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic x-ray background. hard x-ray (e > 10 kev) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify compton-thick (ct, {log} {n}{{h}}≥slant 24) active galactic nuclei (agns). in this letter we present the first results of the largest broadband (0.3-150 kev) x-ray spectral study of hard x-ray selected agns to date, focusing on the properties of heavily obscured sources. our sample includes the 834 agns (728 non-blazar, average redshift z ≃ 0.055) reported in the 70-month catalog of the all-sky hard x-ray swift/burst alert monitor survey. we find 55 ct agns, which represent {7.6}-2.1+1.1% of our non-blazar sample. of these, 26 are reported as candidate ct agns for the first time. we correct for selection bias and derive the intrinsic column density distribution of agns in the local universe in two different luminosity ranges. we find a significant decrease in the fraction of obscured compton-thin agns for increasing luminosity, from 46 ± 3% (for {log}\{l}14-195 = 40-43.7) to 39 ± 3% (for {log}\{l}14-195 = 43.7-46). a similar trend is also found for ct agns. the intrinsic fraction of ct agns with {log}\{n}{{h}} = 24-25 normalized to unity in the {log}\{n}{{h}} = 20-25 range is 27 ± 4%, and is consistent with the observed value obtained for agns located within 20 mpc. | compton-thick accretion in the local universe |
quasars have long been known to be variable sources at all wavelengths. their optical variability is stochastic and can be due to a variety of physical mechanisms; it is also well-described statistically in terms of a damped random walk model. the recent availability of large collections of astronomical time series of flux measurements (light curves) offers new data sets for a systematic exploration of quasar variability. here we report the detection of a strong, smooth periodic signal in the optical variability of the quasar pg 1302-102 with a mean observed period of 1,884 +/- 88 days. it was identified in a search for periodic variability in a data set of light curves for 247,000 known, spectroscopically confirmed quasars with a temporal baseline of about 9 years. although the interpretation of this phenomenon is still uncertain, the most plausible mechanisms involve a binary system of two supermassive black holes with a subparsec separation. such systems are an expected consequence of galaxy mergers and can provide important constraints on models of galaxy formation and evolution. | a possible close supermassive black-hole binary in a quasar with optical periodicity |
we present a detection of 21 cm emission from large-scale structure (lss) between redshift 0.78 and 1.43 made with the canadian hydrogen intensity mapping experiment. radio observations acquired over 102 nights are used to construct maps that are foreground filtered and stacked on the angular and spectral locations of luminous red galaxies (lrgs), emission-line galaxies (elgs), and quasars (qsos) from the eboss clustering catalogs. we find decisive evidence for a detection when stacking on all three tracers of lss, with the logarithm of the bayes factor equal to 18.9 (lrg), 10.8 (elg), and 56.3 (qso). an alternative frequentist interpretation, based on the likelihood ratio test, yields a detection significance of 7.1σ (lrg), 5.7σ (elg), and 11.1σ (qso). these are the first 21 cm intensity mapping measurements made with an interferometer. we constrain the effective clustering amplitude of neutral hydrogen (h i), defined as ${{ \mathcal a }}_{{\rm{h}}\,{\rm\small{i}}}\equiv {10}^{3}\,{{\rm{\omega }}}_{{\rm{h}}\,{\rm\small{i}}}\left({b}_{{\rm{h}}\,{\rm\small{i}}}+\langle \,f{\mu }^{2}\rangle \right)$ , where ωh iis the cosmic abundance of h i, b h iis the linear bias of h i, and <f μ 2> = 0.552 encodes the effect of redshift-space distortions at linear order. we find ${{ \mathcal a }}_{{\rm{h}}\,{\rm\small{i}}}={1.51}_{-0.97}^{+3.60}$ for lrgs (z = 0.84), ${{ \mathcal a }}_{{\rm{h}}\,{\rm\small{i}}}={6.76}_{-3.79}^{+9.04}$ for elgs (z = 0.96), and ${{ \mathcal a }}_{{\rm{h}}\,{\rm\small{i}}}={1.68}_{-0.67}^{+1.10}$ for qsos (z = 1.20), with constraints limited by modeling uncertainties at nonlinear scales. we are also sensitive to bias in the spectroscopic redshifts of each tracer, and we find a nonzero bias δ v = - 66 ± 20 km s-1 for the qsos. we split the qso catalog into three redshift bins and have a decisive detection in each, with the upper bin at z = 1.30 producing the highest-redshift 21 cm intensity mapping measurement thus far. | detection of cosmological 21 cm emission with the canadian hydrogen intensity mapping experiment |
we present a catalog of continuum and emission-line properties for 750,414 broad-line quasars included in the sloan digital sky survey data release 16 quasar catalog (dr16q), measured from optical spectroscopy. these quasars cover broad ranges in redshift (0.1 ≲ z ≲ 6) and luminosity (44 ≲ log(l bol/erg s-1) ≲ 48), and probe lower luminosities than an earlier compilation of sdss dr7 quasars. derived physical quantities such as single-epoch virial black hole masses and bolometric luminosities are also included in this catalog. we present improved systemic redshifts and realistic redshift uncertainties for dr16q quasars using the measured line peaks and correcting for velocity shifts of various lines with respect to the systemic velocity. about 1%, 1.4%, and 11% of the original dr16q redshifts deviate from the systemic redshifts by ∣δv∣ > 1500 km s-1, ∣δv∣ ∈ [1000, 1500] km s-1, and ∣δv∣ ∈ [500, 1000] km s-1, respectively; about 1900 dr16q redshifts were catastrophically wrong (∣δv∣ > 10,000 km s-1). we demonstrate the utility of this data product in quantifying the spectral diversity and correlations among physical properties of quasars with large statistical samples. | a catalog of quasar properties from sloan digital sky survey data release 16 |
mrk 231 is a nearby ultra-luminous ir galaxy exhibiting a kpc-scale, multi-phase agn-driven outflow. this galaxy represents the best target to investigate in detail the morphology and energetics of powerful outflows, as well as their still poorly-understood expansion mechanism and impact on the host galaxy. in this work, we present the best sensitivity and angular resolution maps of the molecular disk and outflow of mrk 231, as traced by co(2-1) and (3-2) observations obtained with the iram/pdbi. in addition, we analyze archival deep chandra and nustar x-ray observations. we use this unprecedented combination of multi-wavelength data sets to constrain the physical properties of both the molecular disk and outflow, the presence of a highly-ionized ultra-fast nuclear wind, and their connection. the molecular co(2-1) outflow has a size of 1 kpc, and extends in all directions around the nucleus, being more prominent along the south-west to north-east direction, suggesting a wide-angle biconical geometry. the maximum projected velocity of the outflow is nearly constant out to 1 kpc, thus implying that the density of the outflowing material must decrease from the nucleus outwards as r-2. this suggests that either a large part of the gas leaves the flow during its expansion or that the bulk of the outflow has not yet reached out to 1 kpc, thus implying a limit on its age of 1 myr. mapping the mass and energy rates of the molecular outflow yields dot {m} of = [500-1000] m⊙ yr-1 and ėkin,of = [7-10] × 1043 erg s-1. the total kinetic energy of the outflow is ekin,of is of the same order of the total energy of the molecular disk, edisk. remarkably, our analysis of the x-ray data reveals a nuclear ultra-fast outflow (ufo) with velocity -20 000 km s-1, dot {m}ufo = [0.3-2.1] m⊙ yr-1, and momentum load dot {p}ufo/ dot {p}rad = [0.2-1.6]. we find ėkin,ufo ėkin,of as predicted for outflows undergoing an energy conserving expansion. this suggests that most of the ufo kinetic energy is transferred to mechanical energy of the kpc-scale outflow, strongly supporting that the energy released during accretion of matter onto super-massive black holes is the ultimate driver of giant massive outflows. the momentum flux dot {p}of derived for the large scale outflows in mrk 231 enables us to estimate a momentum boost dot {p}of/ dot {p} ufo ≈ [30-60]. the ratios ėkin,ufo/lbol,agn = [1-5] % and ėkin,of/lbol,agn = [1-3] % agree with the requirements of the most popular models of agn feedback. based on observations carried out with the iram plateau de bure interferometer. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain), and with chandra and nustar observatories. | the multi-phase winds of markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow |
intermediate-mass black holes (imbhs), with masses in the range 100-106m⊙, are the link between stellar-mass bhs and supermassive bhs (smbhs). they are thought to be the seeds from which smbhs grow, which would explain the existence of quasars with bh masses of up to 1010m⊙ when the universe was only 0.8 gyr old. the detection and study of imbhs has thus strong implications for understanding how smbhs form and grow, which is ultimately linked to galaxy formation and growth, as well as for studies of the universality of bh accretion or the epoch of reionization. proving the existence of seed bhs in the early universe is not yet feasible with the current instrumentation; however, those seeds that did not grow into smbhs can be found as imbhs in the nearby universe. in this review, i summarize the different scenarios proposed for the formation of imbhs and gather all the observational evidence for the few hundreds of nearby imbh candidates found in dwarf galaxies, globular clusters, and ultraluminous x-ray sources, as well as the possible discovery of a few seed bhs at high redshift. i discuss some of their properties, such as x-ray weakness and location in the bh mass scaling relations, and the possibility to discover imbhs through high velocity clouds, tidal disruption events, gravitational waves, or accretion disks in active galactic nuclei. i finalize with the prospects for the detection of imbhs with up-coming observatories. | observational evidence for intermediate-mass black holes |
context. the second release of gaia data (gaia dr2) contains the astrometric parameters for more than half a million quasars. this set defines a kinematically non-rotating reference frame in the optical domain. a subset of these quasars have accurate vlbi positions that allow the axes of the reference frame to be aligned with the international celestial reference system (icrf) radio frame.aims: we describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of gaia dr2 (gaia-crf2), and to compare the optical and radio positions for sources with accurate vlbi positions.methods: descriptive statistics are used to characterise the overall properties of the quasar sample. residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. positional differences are calculated relative to a prototype version of the forthcoming icrf3.results: gaia-crf2 consists of the positions of a sample of 556 869 sources in gaia dr2, obtained from a positional cross-match with the icrf3-prototype and allwise agn catalogues. the sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range g ≃ 16 to 21 mag with accurately known optical positions. the median positional uncertainty is 0.12 mas for g < 18 mag and 0.5 mas at g = mag. large-scale systematics are estimated to be in the range 20 to 30 μas. the accuracy claims are supported by the parallaxes and proper motions of the quasars in gaia dr2. the optical positions for a subset of 2820 sources in common with the icrf3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions.conclusions: based on less than 40% of the data expected from the nominal gaia mission, gaia-crf2 is the first realisation of a non-rotating global optical reference frame that meets the icrs prescriptions, meaning that it is built only on extragalactic sources. its accuracy matches the current radio frame of the icrf, but the density of sources in all parts of the sky is much higher, except along the galactic equator. | gaia data release 2. the celestial reference frame (gaia-crf2) |
the recent tentative detection by the experiment to detect the global eor signature (edges) low band of the hydrogen 21-cm line from cosmic dawn, if confirmed, is the first ever signature observed from the epoch of primordial star formation. however, the magnitude and the shape of this signal are incompatible with standard astrophysical predictions, requiring either colder than expected gas, or an excess radio background above the cosmic microwave background (cmb) radiation. in this paper, we explore the latter option, investigating possible 21-cm signals in models with standard astrophysics to which a phenomenological excess radio background was added. assuming uniform radiation with a synchrotron-like spectrum and redshift-independent amplitude existing throughout cosmic history, we show that such a radio background, in addition to explaining the edges detection, enhances the cosmic dawn power spectrum. the signal during cosmic dawn and re-ionization strongly depends on both the intensity of the background and the astrophysical parameters. we verify the broad agreement of our models with the detected feature, including additional constraints from the edges high-band, high-redshift quasars, and observational limits on the extra-galactic radio background. the data imply a lower limit on the star formation efficiency of 2.8 per cent, an upper limit on the minimum mass of star-forming haloes of mh = 109 m⊙ at z = 17, and a lower limit on the excess background of 1.9 times the cmb at 78 mhz. the properties of x-ray sources are unconstrained by the data. we also show that during the dark ages, such a radio background leaves smoking gun signature in the 21-cm signal. | signature of excess radio background in the 21-cm global signal and power spectrum |
we present a systematic search for changing-look quasars based on repeat photometry from sloan digital sky survey (sdss) and pan-starrs1, along with repeat spectra from sdss and sdss-iii baryon oscillation spectroscopic survey. objects with large, |δg| > 1 mag photometric variations in their light curves are selected as candidates to look for changes in broad emission line (bel) features. out of a sample of 1011 objects that satisfy our selection criteria and have more than one epoch of spectroscopy, we find 10 examples of quasars that have variable and/or `changing-look' bel features. four of our objects have emerging bels, five have disappearing bels, and one object shows tentative evidence for having both emerging and disappearing bels. with redshifts in the range 0.20 < z < 0.63, this sample includes the highest redshift changing-look quasars discovered to date. we highlight the quasar j102152.34+464515.6 at z = 0.204. here, not only have the balmer emission lines strongly diminished in prominence, including hβ all but disappearing, but the blue continuum fν∝ν1/3 typical of an active galactic nuclei is also significantly diminished in the second epoch of spectroscopy. using our selection criteria, we estimate that >15 per cent of strongly variable luminous quasars display changing-look bel features on rest-frame time-scales of 8 to 10 yr. plausible time-scales for variable dust extinction are factors of 2-10 too long to explain the dimming and brightening in these sources, and simple dust reddening models cannot reproduce the bel changes. on the other hand, an advancement such as disc reprocessing is needed if the observed variations are due to accretion rate changes. | a systematic search for changing-look quasars in sdss |
we present reverberation mapping results from the first year of combined spectroscopic and photometric observations of the sloan digital sky survey reverberation mapping project. we successfully recover reverberation time delays between the g+i band emission and the broad hβ emission line for a total of 44 quasars, and for the broad hα emission line in 18 quasars. time delays are computed using the javelin and cream software and the traditional interpolated cross-correlation function (iccf): using well-defined criteria, we report measurements of 32 hβ and 13 hα lags with javelin, 42 hβ and 17 hα lags with cream, and 16 hβ and eight hα lags with the iccf. lag values are generally consistent among the three methods, though we typically measure smaller uncertainties with javelin and cream than with the iccf, given the more physically motivated light curve interpolation and more robust statistical modeling of the former two methods. the median redshift of our hβ-detected sample of quasars is 0.53, significantly higher than that of the previous reverberation mapping sample. we find that in most objects, the time delay of the hα emission is consistent with or slightly longer than that of hβ. we measure black hole masses using our measured time delays and line widths for these quasars. these black hole mass measurements are mostly consistent with expectations based on the local {m}{bh}-{σ }*relationship, and are also consistent with single-epoch black hole mass measurements. this work increases the current sample size of reverberation-mapped active galaxies by about two-thirds and represents the first large sample of reverberation mapping observations beyond the local universe (z < 0.3). | the sloan digital sky survey reverberation mapping project: hα and hβ reverberation measurements from first-year spectroscopy and photometry |
we present measurements of black hole masses and eddington ratios (λ edd) for a sample of 38 bright (m 1450 < -24.4 mag) quasars at 5.8 ≲ z ≲ 7.5, derived from very large telescope/x-shooter near-ir spectroscopy of their broad c iv and mg ii emission lines. the black hole masses (on average, m bh ~ 4.6 × 109 m ⊙) and accretion rates (0.1 ≲ λ edd ≲ 1.0) are broadly consistent with that of similarly luminous 0.3 ≲ z ≲ 2.3 quasars, but there is evidence for a mild increase in the eddington ratio above z ≳ 6. combined with deep atacama large millimeter/submillimeter array (alma) observations of the [c ii] 158 μm line from the host galaxies and vlt/muse investigations of the extended lyα halos, this study provides fundamental clues to models of the formation and growth of the first massive galaxies and black holes. compared to local scaling relations, z ≳ 5.7 black holes appear to be over-massive relative to their hosts, with accretion properties that do not change with host galaxy morphologies. assuming that the kinematics of the t ~ 104 k gas, traced by the extended lyα halos, are dominated by the gravitational potential of the dark matter halo, we observe a similar relation between black hole mass and circular velocity as reported for z ~ 0 galaxies. these results paint a picture where the first supermassive black holes reside in massive halos at z ≳ 6 and lead the first stages of galaxy formation by rapidly growing in mass with a duty cycle of order unity. the duty cycle needs to drastically drop toward lower redshifts, while the host galaxies continue forming stars at a rate of hundreds of solar masses per year, sustained by the large reservoirs of cool gas surrounding them. | the x-shooter/alma sample of quasars in the epoch of reionization. ii. black hole masses, eddington ratios, and the formation of the first quasars |
we introduce version 2.0 of the shark semi-analytic model of galaxy formation after many improvements to the physics included. the most significant being: (i) a model describing the exchange of angular momentum (am) between the interstellar medium and stars; (ii) a new active galactic nuclei feedback model which has two modes, a quasar and a radio mode, with the radio mode tied to the jet energy production; (iii) a model tracking the development of black hole (bh) spins; (iv) more sophisticated modelling of environmental effects on satellite galaxies; and (v) automatic parameter exploration using particle swarm optimisation. we focus on two timely research topics: the structural properties of galaxies and the quenching of massive galaxies. for the former, shark v2.0 is capable of producing a more realistic stellar size-mass relation with a plateau marking the transition from disk- to bulge-dominated galaxies, and scaling relations between specific am and mass that agree well with observations. for the quenching of massive galaxies, shark v2.0 produces massive galaxies that are more quenched than the previous version, reproducing well the observed relations between star formation rate (sfr) and stellar mass, and specific sfr and bh mass at $z=0$. shark v2.0 produces a number density of massive-quiescent galaxies >1dex higher than the previous version, in good agreement with jwst observations at $z\le 5$; predicts a stellar mass function of passive galaxies in reasonably good agreement with observations at $0.5<z<5$; and environmental quenching to already be effective at $z=5$. | quenching massive galaxies across cosmic time with the semi-analytic model shark v2.0 |
we present the obelisk project, a cosmological radiation-hydrodynamics simulation that follows the assembly and reionization of a protocluster progenitor during the first two billion years after the big bang, down to z = 3.5. the simulation resolves haloes down to the atomic cooling limit and tracks the contribution of different sources of ionization: stars, active galactic nuclei, and collisions. the obelisk project is specifically designed to study the coevolution of high-redshift galaxies and quasars in an environment favouring black hole growth. in this paper, we establish the relative contribution of these two sources of radiation to reionization and their respective role in establishing and maintaining the high-redshift ionizing background. our volume is typical of an overdense region of the universe and displays star formation rate and black hole accretion rate densities similar to those of high-redshift protoclusters. we find that hydrogen reionization happens inside-out, is completed by z ∼ 6 in our overdensity, and is predominantly driven by galaxies, while accreting black holes only play a role at z ∼ 4. | the obelisk simulation: galaxies contribute more than agn to h i reionization of protoclusters |
we present a study of the [c ii] 158 μm line and underlying far-infrared (fir) continuum emission of 27 quasar host galaxies at z ∼ 6, traced by the atacama large millimeter/submillimeter array at a spatial resolution of ∼1 physical kpc. the [c ii] emission in the bright, central regions of the quasars have sizes of 1.0-4.8 kpc. the dust continuum emission is typically more compact than [c ii]. we find that 13/27 quasars (approximately one-half) have companion galaxies in the field, at projected separations of 3-90 kpc. the position of dust emission and the gaia-corrected positions of the central accreting black holes are cospatial (typical offsets ≲0"1). this suggests that the central black holes are located at the bottom of the gravitational wells of the dark matter halos in which the $z\gt 6$ quasar hosts reside. some outliers with offsets of ∼500 pc can be linked to disturbed morphologies, most likely due to ongoing or recent mergers. we find no correlation between the central brightness of the fir emission and the bolometric luminosity of the accreting black hole. the fir-derived star formation rate densities (sfrds) in the host galaxies peak at the galaxies' centers, at typical values between 100 and 1000 m⊙ yr-1 kpc-2. these values are below the eddington limit for star formation, but similar to those found in local ultraluminous infrared galaxies. the sfrds drop toward larger radii by an order of magnitude. likewise, the [c ii]/fir luminosity ratios of the quasar hosts are lowest in their centers (few ×10-4) and increase by a factor of a few toward the galaxies' outskirts, consistent with resolved studies of lower-redshift sources. | kiloparsec-scale alma imaging of [c ii] and dust continuum emission of 27 quasar host galaxies at z ∼ 6 |
we present the first joint analysis of catalogs of radio galaxies and quasars to determine whether their sky distribution is consistent with the standard λcdm model of cosmology. this model is based on the cosmological principle, which asserts that the universe is statistically isotropic and homogeneous on large scales, so the observed dipole anisotropy in the cosmic microwave background (cmb) must be attributed to our local peculiar motion. we test the null hypothesis that there is a dipole anisotropy in the sky distribution of radio galaxies and quasars consistent with the motion inferred from the cmb, as is expected for cosmologically distant sources. our two samples, constructed respectively from the nrao vla sky survey and the wide-field infrared survey explorer, are systematically independent and have no shared objects. using a completely general statistic that accounts for correlation between the found dipole amplitude and its directional offset from the cmb dipole, the null hypothesis is independently rejected by the radio galaxy and quasar samples with p-values of 8.9 × 10-3 and 1.2 × 10-5, respectively, corresponding to 2.6σ and 4.4σ significance. the joint significance, using sample-size-weighted z-scores, is 5.1σ. we show that the radio galaxy and quasar dipoles are consistent with each other and find no evidence for any frequency dependence of the amplitude. the consistency of the two dipoles improves if we boost to the cmb frame assuming its dipole to be fully kinematic, suggesting that cosmologically distant radio galaxies and quasars may have an intrinsic anisotropy in this frame. | a challenge to the standard cosmological model |
we present cosmological hydrodynamic simulations of a quasar-mass halo (mhalo ≈ 1012.5 m⊙ at z = 2) that for the first time resolve gas transport down to the inner 0.1 pc surrounding the central massive black hole. we model a multiphase interstellar medium including stellar feedback by supernovae, stellar winds, and radiation, and a hyper-lagrangian refinement technique increasing the resolution dynamically approaching the black hole. we do not include black hole feedback. we show that the subpc inflow rate (1) can reach ~6 m⊙ yr-1 roughly in steady state during the epoch of peak nuclear gas density (z ~ 2), sufficient to power a luminous quasar, (2) is highly time variable in the pre-quasar phase, spanning 0.001-10 m⊙ yr-1 on myr timescales, and (3) is limited to short (~2 myr) active phases (0.01-0.1 m⊙ yr-1) followed by longer periods of inactivity at lower nuclear gas density and late times (z ~ 1), owing to the formation of a hot central cavity. inflowing gas is primarily cool, rotational support dominates over turbulence and thermal pressure, and star formation can consume as much gas as provided by inflows across 1 pc-10 kpc. gravitational torques from multiscale stellar non-axisymmetries dominate angular momentum transport over gas self-torquing and pressure gradients, with accretion weakly dependent on black hole mass. subpc inflow rates correlate with nuclear (but decouple from global) star formation and can exceed the eddington rate by ×10. the black hole can move ~10 pc from the galaxy center on ~0.1 myr. accreting gas forms pc-scale, rotationally supported, obscuring structures often misaligned with the galaxy-scale disk. these simulations open a new avenue to investigate black hole-galaxy coevolution. | cosmological simulations of quasar fueling to subparsec scales using lagrangian hyper-refinement |
recent intensive swift monitoring of the seyfert 1 galaxy ngc 5548 yielded 282 usable epochs over 125 days across six uv/optical bands and the x-rays. this is the densest extended active galactic nucleus (agn) uv/optical continuum sampling ever obtained, with a mean sampling rate <0.5 day. approximately daily hubble space telescope uv sampling was also obtained. the uv/optical light curves show strong correlations ({{r}max }=0.57-0.90) and the clearest measurement to date of interband lags. these lags are well-fit by a τ \propto {{{λ }}4/3} wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of ∼ 0.35+/- 0.05 lt-day at 1367 å, assuming a simple face-on model. the u band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to balmer continuum emission from the broad-line region as suggested by korista and goad. the uv/x-ray correlation is weaker ({{r}max }\lt 0.45) and less consistent over time. this indicates that while swift is beginning to measure uv/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with x-ray variability is less well understood. combining this accretion disk size estimate with those from quasar microlensing studies suggests that agn disk sizes scale approximately linearly with central black hole mass over a wide range of masses. | space telescope and optical reverberation mapping project. ii. swift and hst reverberation mapping of the accretion disk of ngc 5548 |
according to the virial theorem, all gravitational systems in equilibrium sit on a plane in the three-dimensional parameter space defined by their mass, size, and second moment of the velocity tensor. while these quantities cannot be directly observed, there are suitable proxies: the luminosity lk , half-light radius re , and dispersion {σ }e. these proxies indeed lie on a very tight fundamental plane (fp). how do the black holes (bhs) in the centers of galaxies relate to the fp? their masses are known to exhibit no strong correlation with total galaxy mass, but they do correlate weakly with bulge mass (when present), and extremely well with the velocity dispersion through the {m}\bullet \propto {σ }e5.4 relation. these facts together imply that a tight plane must also exist defined by bh mass, total galaxy mass, and size. here, i show that this is indeed the case using a heterogeneous set of 230 bhs. the sample includes bhs from zero to 10 billion solar masses and host galaxies ranging from low surface brightness dwarfs, through bulgeless disks, to brightest cluster galaxies. the resulting bh-size-luminosity relation {m}\bullet \propto {({l}k/{r}e)}3.8 has the same amount of scatter as the m •-σ relation and is aligned with the galaxy fp, such that it is just a reprojection of {σ }e. the inferred bh-size-mass relation is {m}\bullet \propto {({m}\star /{r}e)}2.9. these relationships are universal and extend to galaxies without bulges. this implies that the bh is primarily correlated with its global velocity dispersion and not with the properties of the bulge. i show that the classical bulge-mass relation is a projection of the m •-σ relation. when the velocity dispersion cannot be measured (at high z or low dispersions), the bh-size-mass relation should be used as a proxy for bh mass in favor of just galaxy or bulge mass. | unification of the fundamental plane and super massive black hole masses |
the transmission of lyman α (ly α) in the spectra of distant quasars depends on the density, temperature, and ionization state of the intergalactic medium. therefore, high-redshift (z > 5) ly α forests could be invaluable in studying the late stages of the epoch of reionization (eor), as well as properties of the sources that drive it. indeed, high-quality quasar spectra have now firmly established the existence of large-scale opacity fluctuations at z > 5, whose physical origins are still debated. here, we introduce a bayesian framework capable of constraining the eor and galaxy properties by forward-modelling the high-z ly α forest. using priors from galaxy and cosmic microwave background observations, we demonstrate that the final overlap stages of the eor (when >95 per cent of the volume was ionized) should occur at z < 5.6, in order to reproduce the large-scale opacity fluctuations seen in forest spectra. however, it is the combination of patchy reionization and the inhomogeneous ultraviolet background that produces the longest gunn-peterson troughs. ly α forest observations tighten existing constraints on the characteristic ionizing escape fraction of galaxies, with the combined observations suggesting $f_{\rm esc} \approx 7^{+4}_{-3}$ per cent, and disfavouring a strong evolution with the galaxy's halo (or stellar) mass. | reionization and galaxy inference from the high-redshift ly α forest |
hierarchical assembly models predict a population of supermassive black hole (smbh) binaries. these are not resolvable by direct imaging but may be detectable via periodic variability (or nanohertz frequency gravitational waves). following our detection of a 5.2-year periodic signal in the quasar pg 1302-102, we present a novel analysis of the optical variability of 243 500 known spectroscopically confirmed quasars using data from the catalina real-time transient survey (crts) to look for close (<0.1 pc) smbh systems. looking for a strong keplerian periodic signal with at least 1.5 cycles over a baseline of nine years, we find a sample of 111 candidate objects. this is in conservative agreement with theoretical predictions from models of binary smbh populations. simulated data sets, assuming stochastic variability, also produce no equivalent candidates implying a low likelihood of spurious detections. the periodicity seen is likely attributable to either jet precession, warped accretion discs or periodic accretion associated with a close smbh binary system. we also consider how other smbh binary candidates in the literature appear in crts data and show that none of these are equivalent to the identified objects. finally, the distribution of objects found is consistent with that expected from a gravitational-wave-driven population. this implies that circumbinary gas is present at small orbital radii and is being perturbed by the black holes. none of the sources is expected to merge within at least the next century. this study opens a new unique window to study a population of close smbh binaries that must exist according to our current understanding of galaxy and smbh evolution. | a systematic search for close supermassive black hole binaries in the catalina real-time transient survey |
we present 5321 mas-resolution total intensity and linear polarization maps of 437 active galactic nuclei (agns) obtained with the vlba at 15 ghz as part of the mojave survey, and also from the nrao data archive. the former is a long-term program to study the structure and evolution of powerful parsec-scale outflows associated with agns. the targeted agns are drawn from several flux-limited radio and γ-ray samples, and all have correlated vlba flux densities greater than ∼50 mjy at 15 ghz. approximately 80% of these agns are associated with γ-ray sources detected by the fermi lat instrument. the vast majority were observed with the vlba on 5-15 occasions between 1996 january 19 and 2016 december 26, at intervals ranging from a month to several years, with the most typical sampling interval being six months. a detailed analysis of the linear and circular polarization evolutions of these agn jets is presented in the other papers in this series. | mojave. xv. vlba 15 ghz total intensity and polarization maps of 437 parsec-scale agn jets from 1996 to 2017 |
observations indicate that nearly all galaxies contain supermassive black holes at their centers. when galaxies merge, their component black holes form smbh binaries (smbhbs), which emit low-frequency gravitational waves (gws) that can be detected by pulsar timing arrays. we have searched the north american nanohertz observatory for gravitational waves 11 yr data set for gws from individual smbhbs in circular orbits. as we did not find strong evidence for gws in our data, we placed 95% upper limits on the strength of gws from such sources. at {f}gw} = 8 nhz, we placed a sky-averaged upper limit of h 0 < 7.3(3) × 10-15. we also developed a technique to determine the significance of a particular signal in each pulsar using “dropout” parameters as a way of identifying spurious signals. from these upper limits, we ruled out smbhbs emitting gws with {f}gw} = 8 nhz within 120 mpc for { \mathcal m }={10}9 {m}⊙ , and within 5.5 gpc for { \mathcal m }={10}10 {m}⊙at our most sensitive sky location. we also determined that there are no smbhbs with { \mathcal m }> 1.6× {10}9 {m}⊙emitting gws with {f}gw} = 2.8-317.8 nhz in the virgo cluster. finally, we compared our strain upper limits to simulated populations of smbhbs, based on galaxies in the two micron all-sky survey and merger rates from the illustris cosmological simulation project, and found that only 34 out of 75,000 realizations of the local universe contained a detectable source. | the nanograv 11 yr data set: limits on gravitational waves from individual supermassive black hole binaries |
the study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. this review describes the current status of this field and highlights promising recent findings related to galaxy formation in the densest regions of the early universe. we discuss the main search techniques and the characteristic properties of protoclusters in observations and simulations, and show that protoclusters will have present-day masses similar to galaxy clusters when fully collapsed. we discuss the physical properties of galaxies in protoclusters, including (proto-)brightest cluster galaxies, and the forming red sequence. we highlight the fact that the most massive halos at high redshift are found in protoclusters, making these objects uniquely suited for testing important recent models of galaxy formation. we show that galaxies in protoclusters should be among the first galaxies at high redshift making the transition from a gas cooling regime dominated by cold streams to a regime dominated by hot intracluster gas, which could be tested observationally. we also discuss the possible connections between protoclusters and radio galaxies, quasars, and lyα blobs. because of their early formation, large spatial sizes and high total star-formation rates, protoclusters have also likely played a crucial role during the epoch of reionization, which can be tested with future experiments that will map the neutral and ionized cosmic web. lastly, we review a number of promising observational projects that are expected to make significant impact in this growing, exciting field. | the realm of the galaxy protoclusters. a review |
we review results from cosmic x-ray surveys of active galactic nuclei (agns) over the past years that have dramatically improved our understanding of growing supermassive black holes in the distant universe. first, we discuss the utility of such surveys for agn investigations and the capabilities of the missions making these surveys, emphasizing chandra, xmm-newton, and nustar. second, we briefly describe the main cosmic x-ray surveys, the essential roles of complementary multiwavelength data, and how agns are selected from these surveys. we then review key results from these surveys on the agn population and its evolution ("demographics"), the physical processes operating in agns ("physics"), and the interactions between agns and their environments ("ecology"). we conclude by describing some significant unresolved questions and prospects for advancing the field. | cosmic x-ray surveys of distant active galaxies. the demographics, physics, and ecology of growing supermassive black holes |
we present measurements of the mean and scatter of the intergalactic medium (igm) lyman-α opacity at 4.9 < z < 6.1 along the lines of sight of 62 quasars at zsource> 5.7, the largest sample assembled at these redshifts to date by a factor of two. the sample size enables us to sample cosmic variance at these redshifts more robustly than ever before. the spectra used here were obtained by the sloan digital sky survey, dark energy survey-vista hemisphere survey, and subaru high-z exploration of low-luminosity quasars collaborations, drawn from the echellette spectrograph and imager and x-shooter archives, reused from previous studies or observed specifically for this work. we measure the effective optical depth of lyman-α in bins of 10, 30, 50, and 70 cmpc h-1, construct cumulative distribution functions under two treatments of upper limits on flux and explore an empirical analytic fit to residual lyman-α transmission. we verify the consistency of our results with those of previous studies via bootstrap resampling and confirm the existence of tails towards high values in the opacity distributions, which may persist down to z ∼ 5.2. comparing our results with predictions from cosmological simulations, we find further strong evidence against models that include a spatially uniform ionizing background and temperature-density relation. we also compare to igm models that include either a fluctuating ultraviolet background dominated by rare quasars or temperature fluctuations due to patchy reionization. although both models produce better agreement with the observations, neither fully captures the observed scatter in igm opacity. our sample of 62 z > 5.7 quasar spectra opens many avenues for future study of the reionization epoch. | new constraints on lyman-α opacity with a sample of 62 quasarsat z > 5.7 |
large-scale outflows driven by supermassive black holes are thought to play a fundamental role in suppressing star formation in massive galaxies. however, direct observational evidence for this hypothesis is still lacking, particularly in the young universe where star formation quenching is remarkably rapid, thus requiring effective removal of gas as opposed to slow gas heating. while outflows of ionized gas are commonly detected in massive distant galaxies, the amount of ejected mass is too small to be able to suppress star formation. gas ejection is expected to be more efficient in the neutral and molecular phases, but at high redshift these have only been observed in starbursts and quasars. using deep spectroscopy from jwst, here we show the presence of an outflow of neutral and ionized gas in a massive galaxy observed during the rapid quenching of its star formation, at a redshift of z=2.445. the outflowing mass is mostly in the neutral phase, and the mass outflow rate is larger than the residual star formation rate, indicating that the gas ejection is likely to have a strong impact on the evolution of the galaxy. we do not detect x-ray or radio activity; however the presence of a supermassive black hole is suggested by the properties of the ionized gas emission lines. we thus conclude that supermassive black holes are able to rapidly suppress star formation in massive galaxies by efficiently ejecting neutral gas. | massive and multiphase gas outflow in a quenching galaxy at z=2.445 |
observational information on high-energy astrophysical neutrinos is being continuously collected by the icecube observatory. however, the sources of the neutrinos are still unknown. in this study, we use radio very long baseline interferometry (vlbi) data for a complete vlbi flux density-limited sample of active galactic nuclei (agns). we address the problem of the origin of astrophysical neutrinos with energies above 200 tev in a statistical manner. it is found that agns positionally associated with icecube events have typically stronger parsec-scale cores than the rest of the sample. the posttrial probability of a chance coincidence is 0.2%. we select the four strongest agns as highly probable associations: 3c 279, nrao 530, pks 1741-038, and or 103. moreover, we find an increase of radio emission at frequencies above 10 ghz around neutrino arrival times for several other vlbi-selected agns on the basis of ratan-600 monitoring. the most pronounced example of such behavior is pks 1502+106. we conclude that agns with bright doppler-boosted jets constitute an important population of neutrino sources. high-energy neutrinos are produced in their central parsec-scale regions, probably in proton-photon interactions at or around the accretion disk. radio-bright agns that are likely associated with neutrinos have very diverse γ-ray properties, suggesting that γ-rays and neutrinos may be produced in different regions of agns and not directly related. a small viewing angle of the jet-disk axis is, however, required to detect either of them. | observational evidence for the origin of high-energy neutrinos in parsec-scale nuclei of radio-bright active galaxies |
early results of james webb space telescope observations have delivered bright z ≳ 10 galaxy candidates in greater numbers than expected, enabling construction of rest-frame uv luminosity functions (lfs). the lfs contain key information on the galaxy assembly history, star formation activity, and stellar population of the distant universe. given an upper bound of the total baryonic mass inflow rate to galaxies from their parent halos estimated from abundance matching, we derive a lower bound on the product of the star formation and uv photon production efficiency in galaxies at each redshift. this stringent constraint requires a high efficiency (≳10%-30%) converting gas into stars, assuming a normal stellar population with a salpeter-like mass distribution. the efficiency is substantially higher than those of typical nearby galaxies, but is consistent with those seen in starburst galaxies and super-star clusters observed in the nearby universe. alternatively, the star formation efficiency may be as low as a few percent, which is the average value for the entire galaxy population at z ≃ 6, if the stellar population is metal-free and drawn from a top-heavy mass distribution that produces more intense uv radiation. we discuss several other possible scenarios to achieve the constraint, for instance, energetic radiation produced from compact stellar remnants and quasars, and propose ways to distinguish the scenarios by forthcoming observations. | a lower bound of star formation activity in ultra-high-redshift galaxies detected with jwst: implications for stellar populations and radiation sources |
context. gaia early data release 3 (gaia edr3) provides accurate astrometry for about 1.6 million compact (qso-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions.aims: the proper motions of qso-like sources are used to reveal a systematic pattern due to the acceleration of the solar systembarycentre with respect to the rest frame of the universe. apart from being an important scientific result by itself, the acceleration measured in this way is a good quality indicator of the gaia astrometric solution.methods: theeffect of the acceleration was obtained as a part of the general expansion of the vector field of proper motions in vector spherical harmonics (vsh). various versions of the vsh fit and various subsets of the sources were tried and compared to get the most consistent result and a realistic estimate of its uncertainty. additional tests with the gaia astrometric solution were used to get a better idea of the possible systematic errors in the estimate.results: our best estimate of the acceleration based on gaia edr3 is (2.32 ± 0.16) × 10−10 m s−2 (or 7.33 ±0.51 km s−1 myr−1) towards α = 269.1° ± 5.4°, δ = −31.6° ± 4.1°, corresponding to a proper motion amplitude of 5.05 ±0.35 μas yr−1. this is in good agreement with the acceleration expected from current models of the galactic gravitational potential. we expect that future gaia data releases will provide estimates of the acceleration with uncertainties substantially below 0.1 μas yr−1. movie is only available at https://www.aanda.org | gaia early data release 3. acceleration of the solar system from gaia astrometry |
we present 1625 new 15 ghz (2 cm) vlba images of 295 jets associated with active galactic nuclei (agns) from the mojave and 2 cm vlba surveys, spanning observations between 1994 august 31 and 2013 august 20. for 274 agns with at least 5 vlba epochs, we have analyzed the kinematics of 961 individual bright features in their parsec-scale jets. a total of 122 of these jets have not been previously analyzed by the mojave program. in the case of 451 jet features that had at least 10 epochs, we also examined their kinematics for possible accelerations. at least half of the well-sampled features have non-radial and/or accelerating trajectories, indicating that non-ballistic motion is common in agn jets. since it is impossible to extrapolate any accelerations that occurred before our monitoring period, we could only determine reliable ejection dates for ∼ 24 % of those features that had significant proper motions. the distribution of maximum apparent jet speeds in all 295 agns measured by our program to date is peaked below 5c, with very few jets with apparent speeds above 30c. the fastest speed in our survey is ∼ 50c, measured in the jet of the quasar pks 0805-07, and is indicative of a maximum jet lorentz factor of ∼50 in the parent population. an envelope in the maximum jet speed versus redshift distribution of our sample provides additional evidence of this upper limit to the speeds of radio-emitting regions in parsec-scale agn jets. the fermi-lat-detected gamma-ray agns in our sample have, on average, higher jet speeds than non-lat-detected agns, indicating a strong correlation between parsec-scale jet speed and the gamma-ray doppler boosting factor. we have identified 11 moderate-redshift (z< 0.35) agns with fast apparent speeds (> 10c) that are strong candidates for future tev gamma-ray detection. of the five gamma-ray loud narrow-lined seyfert i agns in our sample, three show highly superluminal jet motions, while the others have sub-luminal speeds. this indicates that some narrow-lined seyfert i agns possess powerful jets with lorentz factors in excess of 10, and viewing angles less than 10^\circ , consistent with those of typical bl lac objects and flat-spectrum radio quasars. | mojave: xiii. parsec-scale agn jet kinematics analysis based on 19 years of vlba observations at 15 ghz |
the first survey, begun over 20 years ago, provides the definitive high-resolution map of the radio sky. this very large telescope (vla) survey reaches a detection sensitivity of 1 mjy at 20 cm over a final footprint of 10,575 deg2 that is largely coincident with the sloan digital sky survey (sdss) area. both the images and a catalog containing 946,432 sources are available through the first web site (http://sundog.stsci.edu). we record here the authoritative survey history, including hardware and software changes that affect the catalog's reliability and completeness. in particular, we use recent observations taken with the jvla to test various aspects of the survey data (astrometry, clean bias, and the flux density scale). we describe a new, sophisticated algorithm for flagging potential sidelobes in this snapshot survey, and show that fewer than 10% of the cataloged objects are likely sidelobes, and that these are heavily concentrated at low flux densities and in the vicinity of bright sources, as expected. we also report a comparison of the survey with the nrao vla sky survey (nvss), as well as a match of the first catalog to the sdss and two micron sky survey (2mass) sky surveys. the nvss match shows very good consistency in flux density scale and astrometry between the two surveys. the matches with 2mass and sdss indicate a systematic ~10-20 mas astrometric error with respect to the optical reference frame in all vla data that has disappeared with the advent of the jvla. we demonstrate strikingly different behavior between the radio matches to stellar objects and to galaxies in the optical and ir surveys reflecting the different radio populations present over the flux density range 1-1000 mjy. as the radio flux density declines, stellar counterparts (quasars) get redder and fainter, while galaxies get brighter and have colors that initially redden but then turn bluer near the first detection limit. implications for future radio sky surveys are also briefly discussed. in particular, we show that for radio source identification at faint optical magnitudes, high angular resolution observations are essential, and cannot be sacrificed in exchange for high signal-to-noise data. the value of a jvla survey as a complement to square kilometer array precursor surveys is briefly discussed. | the last of first: the final catalog and source identifications |
supermassive black hole binaries (smbhbs) at sub-parsec separations should be common in galactic nuclei, as a result of frequent galaxy mergers. hydrodynamical simulations of circum-binary discs predict strong periodic modulation of the mass accretion rate on time-scales comparable to the orbital period of the binary. as a result, smbhbs may be recognized by the periodic modulation of their brightness. we conducted a statistical search for periodic variability in a sample of 35 383 spectroscopically confirmed quasars in the photometric data base of the palomar transient factory (ptf). we analysed lomb-scargle periodograms and assessed the significance of our findings by modelling each individual quasar's variability as a damped random walk (drw). we identified 50 quasars with significant periodicity beyond the drw model, typically with short periods of a few hundred days. we find 33 of these to remain significant after a re-analysis of their periodograms including additional optical data from the intermediate-ptf and the catalina real-time transient survey. assuming that the observed periods correspond to the redshifted orbital periods of smbhbs, we conclude that our findings are consistent with a population of unequal-mass smbhbs, with a typical mass ratio as low as q ≡ m2/m1 ≈ 0.01. | a population of short-period variable quasars from ptf as supermassive black hole binary candidates |
we report a candidate of a low-luminosity active galactic nucleus (agn) at z = 5 that was selected from the first near-infrared images of the jwst ceers project. this source, named ceers-agn-z5-1 at absolute 1450 å magnitude m 1450 = -19.5 ± 0.3, was found via a visual selection of compact sources from a catalog of lyman break galaxies at z > 4, taking advantage of the superb spatial resolution of the jwst/nircam images. the 20 photometric data available from cfht, hubble space telescope, spitzer, and jwst suggest that the continuum shape of this source is reminiscent of that for an unobscured agn, and there is a clear color excess in the filters where the redshifted hβ+[o iii] and hα are covered. the estimated line luminosity is l hβ+[o iii] = 1043.0 erg s-1 and l hα= 1042.9 erg s-1 with the corresponding rest-frame equivalent width ewhβ+[o iii] = 1100 å and ewhα= 1600 å, respectively. our spectral energy distribution fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-eddington accreting black hole (bh), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. the bolometric luminosity, l bol = 2.5 ± 0.3 × 1044 erg s-1, is consistent with those of z < 0.35 broad-line agns with m bh ~ 106 m ⊙ accreting at the eddington limit. this new agn population in the first 1.1 billion years of the universe may close the gap between the observed bh mass range at high redshift and that of bh seeds. spectroscopic confirmation is awaited to secure the redshift and its agn nature. | a candidate for the least-massive black hole in the first 1.1 billion years of the universe |
we present results from a set of high-fidelity simulated lightcones for the desi one-percent survey, created from the uchuu simulation. this 8 (gpc/h)^3 n-body simulation comprises 2.1 trillion particles and provides high-resolution dark matter (sub)haloes in the framework of the planck base-lcdm cosmology. employing the subhalo abundance matching (sham) technique, we populate the uchuu (sub)haloes with all four desi tracers (bgs, lrg, elg and qso) to z = 2.1. our method accounts for redshift evolution as well as the clustering dependence on luminosity and stellar mass. the two-point clustering statistics of the desi one-percent survey align reasonably well with our predictions from uchuu across scales ranging from 0.1 mpc/h to 100 mpc/h. some discrepancies arise due to cosmic variance, incompleteness in the massive end of the stellar mass function, and a simplified galaxy-halo connection model. we find that the uchuu bgs and lrg samples are adequately described using the standard 5-parameter halo occupation distribution model, while the elgs and qsos show agreement with an adopted gaussian distribution for central halos with a power law for satellites. we observe a fair agreement in the large-scale bias measurements between data and mock samples, although the data exhibits smaller bias values, likely due to cosmic variance. the bias dependence on absolute magnitude, stellar mass and redshift aligns with that of previous surveys. these results improve simulated lightcone construction from cosmological models and enhance our understanding of the galaxy-halo connection, with pivotal insights from the first desi data for the success of the final survey. | the desi one-percent survey: modelling the clustering and halo occupation of all four desi tracers with uchuu |
the southern photometric local universe survey (s-plus) is imaging ∼9300 deg2 of the celestial sphere in 12 optical bands using a dedicated 0.8 m robotic telescope, the t80-south, at the cerro tololo inter-american observatory, chile. the telescope is equipped with a 9.2k × 9.2k e2v detector with 10 {μ m} pixels, resulting in a field of view of 2 deg2 with a plate scale of 0.55 arcsec pixel-1. the survey consists of four main subfields, which include two non-contiguous fields at high galactic latitudes (|b| > 30°, 8000 deg2) and two areas of the galactic disc and bulge (for an additional 1300 deg2). s-plus uses the javalambre 12-band magnitude system, which includes the 5 ugriz broad-band filters and 7 narrow-band filters centred on prominent stellar spectral features: the balmer jump/[oii], ca h + k, h δ, g band, mg b triplet, h α, and the ca triplet. s-plus delivers accurate photometric redshifts (δz/(1 + z) = 0.02 or better) for galaxies with r < 19.7 ab mag and z < 0.4, thus producing a 3d map of the local universe over a volume of more than 1 (gpc/h)^3. the final s-plus catalogue will also enable the study of star formation and stellar populations in and around the milky way and nearby galaxies, as well as searches for quasars, variable sources, and low-metallicity stars. in this paper we introduce the main characteristics of the survey, illustrated with science verification data highlighting the unique capabilities of s-plus. we also present the first public data release of ∼336 deg2 of the stripe 82 area, in 12 bands, to a limiting magnitude of r = 21, available at datalab.noao.edu/splus. | the southern photometric local universe survey (s-plus): improved seds, morphologies, and redshifts with 12 optical filters |
we use pantheon type ia supernova (sn ia) apparent magnitude, des-3 yr binned sn ia apparent magnitude, hubble parameter, and baryon acoustic oscillation measurements to constrain six spatially flat and non-flat cosmological models. these sets of data provide mutually consistent cosmological constraints in the six cosmological models we study. a joint analysis of these data sets provides model-independent estimates of the hubble constant, $h_0=68.8\pm 1.8\ \rm {km \, s^{-1} \ mpc^{-1}}$, and the non-relativistic matter density parameter, $\omega _{\rm m_0}=0.294\pm 0.020$. although the joint constraints prefer mild dark energy dynamics and a little spatial curvature, they do not rule out dark energy being a cosmological constant and flat spatial hypersurfaces. we also add quasar angular size and h ii starburst galaxy measurements to the combined data set and find more restrictive constraints. | using pantheon and des supernova, baryon acoustic oscillation, and hubble parameter data to constrain the hubble constant, dark energy dynamics, and spatial curvature |
a key component of the dark energy spectroscopic instrument (desi) survey validation (sv) is a detailed visual inspection (vi) of the optical spectroscopic data to quantify key survey metrics. in this paper we present results from vi of the quasar survey using deep coadded sv spectra. we show that the majority (≈70%) of the main-survey targets are spectroscopically confirmed as quasars, with ≈16% galaxies, ≈6% stars, and ≈8% low-quality spectra lacking reliable features. a nonnegligible fraction of the quasars are misidentified by the standard spectroscopic pipeline, but we show that the majority can be recovered using post-pipeline "afterburner" quasar-identification approaches. we combine these "afterburners" with our standard pipeline to create a modified pipeline to increase the overall quasar yield. at the depth of the main desi survey, both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km s-1) of ≈99%; however, the modified pipeline recovers ≈94% of the visually inspected quasars, as compared to ≈86% from the standard pipeline. we demonstrate that both pipelines achieve a median redshift precision and accuracy of ≈100 km s-1 and ≈70 km s-1, respectively. we constructed composite spectra to investigate why some quasars are missed by the standard pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of "seyfert galaxies") and/or more dust reddened than the standard-pipeline quasars. we also show example spectra to demonstrate the overall diversity of the desi quasar sample and provide strong-lensing candidates where two targets contribute to a single spectrum. | the desi survey validation: results from visual inspection of the quasar survey spectra |
how quasars powered by supermassive black holes formed less than a billion years after the big bang is still one of the outstanding problems in astrophysics, 20 years after their discovery1-4. cosmological simulations suggest that rare cold flows converging on primordial haloes in low-shear environments could have created these quasars if they were 104-105 solar masses at birth, but could not resolve their formation5-8. semi-analytical studies of the progenitor halo of a primordial quasar found that it favours the formation of such seeds, but could not verify if one actually appeared9. here we show that a halo at the rare convergence of strong, cold accretion flows creates massive black holes seeds without the need for ultraviolet backgrounds, supersonic streaming motions or even atomic cooling. cold flows drive violent, supersonic turbulence in the halo, which prevents star formation until it reaches a mass that triggers sudden, catastrophic baryon collapse that forms 31,000 and 40,000 solar-mass stars. this simple, robust process ensures that haloes capable of forming quasars by a redshift of z > 6 produce massive seeds. the first quasars were thus a natural consequence of structure formation in cold dark matter cosmologies, and not exotic, finely tuned environments as previously thought10-14. | turbulent cold flows gave birth to the first quasars |
we present the lens mass model of the quadruply-imaged gravitationally lensed quasar wfi2033 - 4723, and perform a blind cosmographical analysis based on this system. our analysis combines (1) time-delay measurements from 14 yr of data obtained by the cosmological monitoring of gravitational lenses (cosmograil) collaboration, (2) high-resolution hubble space telescope imaging, (3) a measurement of the velocity dispersion of the lens galaxy based on eso-muse data, and (4) multi-band, wide-field imaging and spectroscopy characterizing the lens environment. we account for all known sources of systematics, including the influence of nearby perturbers and complex line-of-sight structure, as well as the parametrization of the light and mass profiles of the lensing galaxy. after unblinding, we determine the effective time-delay distance to be $4784_{-248}^{+399}~\mathrm{mpc}$ , an average precision of $6.6{{\ \rm per\ cent}}$ . this translates to a hubble constant $h_{0} = 71.6_{-4.9}^{+3.8}~\mathrm{km~s^{-1}~mpc^{-1}}$ , assuming a flat λcdm cosmology with a uniform prior on ωm in the range [0.05, 0.5]. this work is part of the h0 lenses in cosmograil's wellspring (h0licow) collaboration, and the full time-delay cosmography results from a total of six strongly lensed systems are presented in a companion paper (h0licow xiii). | h0licow xii. lens mass model of wfi2033-4723 and blind measurement of its time-delay distance and h0 |
context. since july 2014, the gaia mission has been engaged in a high-spatial-resolution, time-resolved, precise, accurate astrometric, and photometric survey of the entire sky.aims: we present the gaia science alerts project, which has been in operation since 1 june 2016. we describe the system which has been developed to enable the discovery and publication of transient photometric events as seen by gaia.methods: we outline the data handling, timings, and performances, and we describe the transient detection algorithms and filtering procedures needed to manage the high false alarm rate. we identify two classes of events: (1) sources which are new to gaia and (2) gaia sources which have undergone a significant brightening or fading. validation of the gaia transit astrometry and photometry was performed, followed by testing of the source environment to minimise contamination from solar system objects, bright stars, and fainter near-neighbours.results: we show that the gaia science alerts project suffers from very low contamination, that is there are very few false-positives. we find that the external completeness for supernovae, ce = 0.46, is dominated by the gaia scanning law and the requirement of detections from both fields-of-view. where we have two or more scans the internal completeness is ci = 0.79 at 3 arcsec or larger from the centres of galaxies, but it drops closer in, especially within 1 arcsec.conclusions: the per-transit photometry for gaia transients is precise to 1% at g = 13, and 3% at g = 19. the per-transit astrometry is accurate to 55 mas when compared to gaia dr2. the gaia science alerts project is one of the most homogeneous and productive transient surveys in operation, and it is the only survey which covers the whole sky at high spatial resolution (subarcsecond), including the galactic plane and bulge. classification tables are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/652/a76. | gaia early data release 3. gaia photometric science alerts |
in the context of observations of the rest-frame ultraviolet and optical emission from distant galaxies, we explore the emission-line properties of photoionization models of active and inactive galaxies. our aim is to identify new line-ratio diagnostics to discriminate between gas photoionization by active galactic nuclei (agn) and star formation. we use a standard photoionization code to compute the emission from agn narrow-line regions and compare this with calculations of the nebular emission from star-forming galaxies achieved using the same code. we confirm the appropriateness of widely used optical spectral diagnostics of nuclear activity versus star formation and explore new diagnostics at ultraviolet wavelengths. we find that combinations of a collisionally excited metal line or line multiplet, such as c iv λλ1548, 1551, o iii] λλ1661, 1666, n iii] λ1750, [si iii] λ1883+si iii] λ1892 and [c iii] λ1907+c iii] λ1909, with the he ii λ1640 recombination line are individually good discriminants of the nature of the ionizing source. diagrams involving at least three of these lines allow an even more stringent distinction between active and inactive galaxies, as well as valuable constraints on interstellar gas parameters and the shape of the ionizing radiation. several line ratios involving ne-based emission lines, such as [ne iv] λ2424, [ne iii] λ3343 and [ne v] λ3426, are also good diagnostics of nuclear activity. our results provide a comprehensive framework to identify the sources of photoionization and physical conditions of the ionized gas from the ultraviolet and optical nebular emission from galaxies. this will be particularly useful to interpret observations of high-redshift galaxies with future facilities, such as the james webb space telescope and extremely large ground-based telescopes. | nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths |
we report new measurements of the intergalactic medium (igm) lyα and lyβ effective optical depth at 5.3 < z < 6.5, using a new sample of quasar sight lines including 32 quasars at 6.308 ≤ z ≤ 7.00. these quasars provide a large statistical sample to measure the igm evolution during the transition phase of the reionization epoch. we construct a data set of deep optical spectra of these quasars using vlt, keck, gemini, lbt, and mmt. we measure the lyα effective optical depth at 5.36 < z < 6.57 using the lyα forests of both individual spectra and the stacked spectrum. the large scatter of individual measurements is consistent with previous work, suggesting an inhomogeneous reionization process. combining our new measurements and previous results, we obtain a best fit for the lyα effective optical depth evolution at z > 5.3, $\tau \propto {\left(1+z\right)}^{8.6\pm 1.0}$ . we then estimate the observed lyβ effective optical depth using lyβ forests and convert them to lyα optical depth for comparison, which provides additional constraints on the evolution of the igm optical depth. the lyβ-based measurements are generally in agreement with the best-fit evolution obtained from lyα forests. using this new sample, we identify 389 lyα and 50 lyβ transmission spikes at 5.5 < z < 6.3. the upper limits of lyα optical depth estimated using transmission spikes are well consistent with our best-fit evolution. the evolution in number density of these high-redshift transmission spikes suggests a rapid transition phase at the end of the reionization. comparison of our optical depth measurements with hydrodynamical simulations indicates an igm neutral hydrogen fraction $\langle {f}_{{\rm{h}}{\rm\small{i}}}\rangle \gtrsim {10}^{-4}$ at z = 6. | measurements of the z ∼ 6 intergalactic medium optical depth and transmission spikes using a new z > 6.3 quasar sample |
we report initial results from a large gemini program to observe z ≳ 5.7 quasars with gnirs near-ir spectroscopy. our sample includes 50 quasars with simultaneous ∼0.85-2.5 μm spectra covering the rest-frame ultraviolet and major broad emission lines from lyα to mg ii. we present spectral measurements for these quasars and compare with their lower redshift counterparts at z = 1.5-2.3. we find that when quasar luminosity is matched, there are no significant differences between the rest-uv spectra of z ≳ 5.7 quasars and the low-z comparison sample. high-z quasars have similar continuum and emission line properties and occupy the same region in the black hole mass and luminosity space as the comparison sample, accreting at an average eddington ratio of ∼0.3. there is no evidence for super-eddington accretion or hypermassive (>1010 m ⊙) black holes within our sample. we find a mild excess of quasars with weak c iv lines relative to the control sample. our results, corroborating earlier studies but with better statistics, demonstrate that these high-z quasars are already mature systems of accreting supermassive black holes operating with the same physical mechanisms as those at lower redshifts. | gemini gnirs near-infrared spectroscopy of 50 quasars at z ≳ 5.7 |
the recent $\sim 4 \, \sigma$ hubble constant, h0, tension is observed between the value of h0 from the cosmic microwave background (cmb) and type ia supernovae (sne ia). it is a decade since this tension is excruciating the modern astrophysical community. to shed light on this problem is key to consider probes at intermediate redshifts between sne ia and cmb and reduce the uncertainty on h0. toward these goals, we fill the redshift gap by employing gamma-ray bursts (grbs) and quasars (qsos), reaching z = 9.4 and z = 7.6, respectively, combined with baryonic acoustic oscillations (bao), and sne ia. to this end, we employ the 'dainotti grb 3d relation' among the rest-frame end time of the x-ray plateau emission, its corresponding luminosity, and the peak prompt luminosity, and the 'risaliti-lusso' qso relation between ultraviolet and x-ray luminosities. we inquire the commonly adopted gaussianity assumption on grbs, qsos, and bao. with the joint sample, we fit the flat λ cold dark matter model with both the gaussian and the newly discovered likelihoods. we also investigate the impact of the calibration assumed for pantheon and pantheon + sne ia on this analysis. remarkably, we show that only grbs fulfil the gaussianity assumption. we achieve small uncertainties on the matter-density parameter ωm and h0. we find h0 values compatible within 2σ with the one from the tip of the red giant branch. finally, we show that the cosmological results are heavily biased against the arbitrary calibration choice for sne ia. | gamma-ray bursts, quasars, baryonic acoustic oscillations, and supernovae ia: new statistical insights and cosmological constraints |
context. the kilo-degree survey (kids) is an ongoing optical wide-field imaging survey with the omegacam camera at the vlt survey telescope. it aims to image 1500 square degrees in four filters (ugri). the core science driver is mapping the large-scale matter distribution in the universe, using weak lensing shear and photometric redshift measurements. further science cases include galaxy evolution, milky way structure, detection of high-redshift clusters, and finding rare sources such as strong lenses and quasars.aims: here we present the third public data release and several associated data products, adding further area, homogenized photometric calibration, photometric redshifts and weak lensing shear measurements to the first two releases.methods: a dedicated pipeline embedded in the astro-wise information system is used for the production of the main release. modifications with respect to earlier releases are described in detail. photometric redshifts have been derived using both bayesian template fitting, and machine-learning techniques. for the weak lensing measurements, optimized procedures based on the theli data reduction and lensfit shear measurement packages are used.results: in this third data release an additional 292 new survey tiles (≈300 deg2) stacked ugri images are made available, accompanied by weight maps, masks, and source lists. the multi-band catalogue, including homogenized photometry and photometric redshifts, covers the combined dr1, dr2 and dr3 footprint of 440 survey tiles (44 deg2). limiting magnitudes are typically 24.3, 25.1, 24.9, 23.8 (5σ in a 2'' aperture) in ugri, respectively, and the typical r-band psf size is less than 0.7''. the photometric homogenization scheme ensures accurate colours and an absolute calibration stable to ≈2% for gri and ≈3% in u. separately released for the combined area of all kids releases to date are a weak lensing shear catalogue and photometric redshifts based on two different machine-learning techniques. | the third data release of the kilo-degree survey and associated data products |
we investigate the correlations between the black hole (bh) mass mbh, the velocity dispersion σ, the bulge mass mbu, the bulge average spherical density {ρ }{{h}}, and its spherical half-mass radius rh, constructing a database of 97 galaxies (31 core ellipticals, 17 power-law ellipticals, 30 classical bulges, and 19 pseudobulges) by joining 72 galaxies from the literature to 25 galaxies observed during our recent sinfoni bh survey. for the first time we discuss the full error covariance matrix. we analyze the well-known mbh-σ and mbh-mbu relations and establish the existence of statistically significant correlations between mbu and rh and anticorrelations between mbu and {ρ }{{h}}. we establish five significant bivariate correlations (mbh-σ-ρh, mbh-σ-rh, mbh-mbu-σ, mbh-mbu-ρh, mbh-mbu-rh) that predict mbh of 77 core and power-law ellipticals and classical bulges with measured and intrinsic scatter as small as ≈ 0.36 dex and ≈ 0.33 dex, respectively, or 0.26 dex when the subsample of 45 galaxies defined by kormendy & ho is considered. in contrast, pseudobulges have systematically lower mbh but approach the predictions of all of the above relations at spherical densities {ρ }{{h}}≥slant {10}10 {m}⊙{{kpc}}-3 or scale lengths {r}{{h}}≤slant 1 {{kpc}}. these findings fit in a scenario of coevolution of bh and classical-bulge masses, where core ellipticals are the product of dry mergers of power-law bulges and power-law ellipticals and bulges the result of (early) gas-rich mergers and of disk galaxies. in contrast, the (secular) growth of bhs is decoupled from the growth of their pseudobulge hosts, except when (gas) densities are high enough to trigger the feedback mechanism responsible for the existence of the correlations between mbh and galaxy structural parameters. | the sinfoni black hole survey: the black hole fundamental plane revisited and the paths of (co)evolution of supermassive black holes and bulges |
risaliti, lusso, and collaborators have constructed a high-redshift hubble diagram of supernovae (sne), quasars (qso), and gamma-ray bursts (grbs) that shows a "∼4 σ tension with the λ cdm model" based on a log polynomial cosmographic expansion [1,2]. in this work, we demonstrate that the log polynomial expansion generically fails to recover flat λ cdm beyond z ∼2 , thus undermining the ∼4 σ tension claim. moreover, through direct fits of both the flat λ cdm and the log polynomial model to the sne +qso +grb data set, we confirm that the flat λ cdm model is preferred. ultimately, we trace the tension to the qso data and show that a best fit of the flat λ cdm model to the qso data leads to a flat λ cdm universe with no dark energy within 1 σ . this marks an irreconcilable tension between the risaliti-lusso qsos and flat λ cdm . | cosmography and flat λ cdm tensions at high redshift |
we explore the kinematics of 27 z ≳ 6 quasar host galaxies observed in [c ii] 158 μm ([c ii]) emission with the atacama large millimeter/submillimeter array at a resolution of ≈0"25. we find that nine of the galaxies show disturbed [c ii] emission, due to either a close companion galaxy or a recent merger. ten galaxies have smooth velocity gradients consistent with the emission arising from a gaseous disk. the remaining eight quasar host galaxies show no velocity gradient, suggesting that the gas in these systems is dispersion dominated. all galaxies show high velocity dispersions with a mean of 129 ± 10 km s-1. to provide an estimate of the dynamical mass within twice the half-light radius of the quasar host galaxy, we model the kinematics of the [c ii] emission line using our publicly available kinematic fitting code, qubefit. this results in a mean dynamical mass of 5.0 ± 0.8( ± 3.5) × 1010 m⊙. comparison between the dynamical mass and the mass of the supermassive black hole reveals that the sample falls above the locally derived bulge mass-black hole mass relation at 2.4σ significance. this result is robust even if we account for the large systematic uncertainties. using several different estimators for the molecular mass, we estimate a gas mass fraction of >10%, indicating that gas makes up a large fraction of the baryonic mass of z ≳ 6 quasar host galaxies. finally, we speculate that the large variety in [c ii] kinematics is an indication that gas accretion onto z ≳ 6 supermassive black holes is not caused by a single precipitating factor. | the kinematics of z ≳ 6 quasar host galaxies |
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