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supermassive black hole (bh) mergers produce powerful gravitational wave emission. asymmetry in this emission imparts a recoil kick to the merged bh, which can eject the bh from its host galaxy altogether. recoiling bhs could be observed as offset active galactic nuclei (agn). several candidates have been identified, but systematic searches have been hampered by large uncertainties regarding their observability. by extracting merging bhs and host galaxy properties from the illustris cosmological simulations, we have developed a comprehensive model for recoiling agn. here, for the first time, we model the effects of bh spin alignment and recoil dynamics based on the gas richness of host galaxies. we predict that if bh spins are not highly aligned, seeing-limited observations could resolve offset agn, making them promising targets for all-sky surveys. for randomly oriented spins, ≲ 10 spatially offset agn may be detectable in hubble space telescope-cosmological evolution survey, and >103 could be found with the panoramic survey telescope & rapid response system (pan-starrs), the large synoptic survey telescope (lsst), euclid, and the wide-field infrared survey telescope (wfirst). nearly a thousand velocity offset agn are predicted within the sloan digital sky survey (sdss) footprint; the rarity of large broad-line offsets among sdss quasars is likely due in part to selection effects but suggests that spin alignment plays a role in suppressing recoils. none the less, in our most physically motivated model where alignment occurs only in gas-rich mergers, hundreds of offset agn should be found in all-sky surveys. our findings strongly motivate a dedicated search for recoiling agn. | recoiling black holes: prospects for detection and implications of spin alignment |
collisions were suggested to potentially play a role in the formation of massive stars in present day clusters, and have likely been relevant during the formation of massive stars and intermediate mass black holes within the first star clusters. in the early universe, the first stellar clusters were particularly dense, as fragmentation typically only occurred at densities above 109 cm-3, and the radii of the protostars were enhanced as a result of larger accretion rates, suggesting a potentially more relevant role of stellar collisions. we present here a detailed parameter study to assess how the number of collisions and the mass growth of the most massive object depend on the properties of the cluster. we also characterize the time evolution with three effective parameters: the time when most collisions occur, the duration of the collisions period, and the normalization required to obtain the total number of collisions. we apply our results to typical population iii (pop. iii) clusters of about 1000 m⊙, finding that a moderate enhancement of the mass of the most massive star by a factor of a few can be expected. for more massive pop. iii clusters as expected in the first atomic cooling halos, we expect a more significant enhancement by a factor of 15-32. we therefore conclude that collisions in massive pop. iii clusters were likely relevant to form the first intermediate mass black holes. | collisions in primordial star clusters. formation pathway for intermediate mass black holes |
we present new constraints on parameters of cosmic dawn and the epoch of reionization derived from the edges high-band spectrum (90-190 mhz). the parameters are probed by evaluating global 21 cm signals generated with the recently developed global21cm tool. this tool uses neural networks trained and tested on ∼30,000 spectra produced with semi-numerical simulations that assume the standard thermal evolution of the cosmic microwave background and the intergalactic medium. from our analysis, we constrain at 68% (1) the minimum virial circular velocity of star-forming halos to v c < 19.3 km s-1, (2) the x-ray heating efficiency of early sources to f x > 0.0042, and (3) the low-energy cutoff of the x-ray spectral energy distribution to ν min < 2.3 kev. we also constrain the star formation efficiency (f *), the electron scattering optical depth (τ e), and the mean-free path of ionizing photons (r mfp). we recompute the constraints after incorporating into the analysis four estimates for the neutral hydrogen fraction from high-z quasars and galaxies, and a prior on τ e from planck 2018. the largest impact of the external observations is on the parameters that most directly characterize reionization. specifically, we derive the combined 68% constraints τ e < 0.063 and r mfp > 27.5 mpc. the external observations also have a significant effect on v c due to its degeneracy with τ e, while the constraints on f *, f x, and ν min, remain primarily determined by edges. | results from edges high-band. iii. new constraints on parameters of the early universe |
we have reprocessed over 100 terabytes of single-exposure wide-field infrared survey explorer (wise)/neowise images to create the deepest ever full-sky maps at 3-5 microns. we include all publicly available w1 and w2 imaging—a total of ∼8 million exposures in each band—from ∼37 months of observations spanning 2010 january to 2015 december. our coadds preserve the native wise resolution and typically incorporate ∼3× more input frames than those of the allwise atlas stacks. our coadds are designed to enable deep forced photometry, in particular for the dark energy camera legacy survey (decals) and mayall z-band legacy survey (mzls), both of which are being used to select targets for the dark energy spectroscopic instrument. we describe newly introduced processing steps aimed at leveraging added redundancy to remove artifacts, with the intent of facilitating uniform target selection and searches for rare/exotic objects (e.g., high-redshift quasars and distant galaxy clusters). forced photometry depths achieved with these coadds extend 0.56 (0.46) magnitudes deeper in w1 (w2) than is possible with only pre-hibernation wise imaging. | deep full-sky coadds from three years of wise and neowise observations |
using hubble space telescope cosmic origins spectrograph observations of 89 qso sightlines through the sloan digital sky survey footprint, we study the relationships between c iv absorption systems and the properties of nearby galaxies, as well as the large-scale environment. to maintain sensitivity to very faint galaxies, we restrict our sample to 0.0015\lt z\lt 0.015, which defines a complete galaxy survey to l≳ 0.01 l\ast or stellar mass {m}* ≳ {10}8 {m}⊙ . we report two principal findings. first, for galaxies with impact parameter ρ \lt 1 {r}{vir}, c iv detection strongly depends on the luminosity/stellar mass of the nearby galaxy. c iv is preferentially associated with galaxies with {m}* \gt {10}9.5 {m}⊙ ; lower-mass galaxies rarely exhibit significant c iv absorption (covering fraction {f}c={9}-6+12 % for 11 galaxies with {m}* \lt {10}9.5 {m}⊙ ). second, c iv detection within the {m}* \gt {10}9.5 {m}⊙population depends on environment. using a fixed-aperture environmental density metric for galaxies with ρ < 160 kpc at z\lt 0.055, we find that {57}-13+12 % (8/14) of galaxies in low-density regions (regions with fewer than seven l\gt 0.15 l\ast galaxies within 1.5 mpc) have affiliated c iv absorption; however, none (0/7) of the galaxies in denser regions show c iv. similarly, the c iv detection rate is lower for galaxies residing in groups with dark matter halo masses of {m}{halo}\gt {10}12.5 {m}⊙ . in contrast to c iv, h i is pervasive in the circumgalactic medium without regard to mass or environment. these results indicate that c iv absorbers with {log} n({{c}} {{iv}})≳ 13.5 {{cm}}-2 trace the halos of {m}* \gt {10}9.5 {m}⊙galaxies but also reflect larger-scale environmental conditions. | a deep search for faint galaxies associated with very low redshift c iv absorbers. iii. the mass- and environment-dependent circumgalactic medium |
we use new precision measurements of black hole (bh) masses from water megamaser disks to investigate scaling relations between macroscopic galaxy properties and supermassive bh mass. the megamaser-derived bh masses span 106-108 {m}⊙ , while all the galaxy properties that we examine (including total stellar mass, central mass density, and central velocity dispersion) lie within a narrower range. thus, no galaxy property correlates tightly with {m}{bh} in ∼l* spiral galaxies as traced by megamaser disks. of them all, stellar velocity dispersion provides the tightest relation, but at fixed {σ }*the mean megamaser {m}{bh} are offset by -0.6 ± 0.1 dex relative to early-type galaxies. spiral galaxies with non-maser dynamical bh masses do not appear to show this offset. at low mass, we do not yet know the full distribution of bh mass at fixed galaxy property; the non-maser dynamical measurements may miss the low-mass end of the bh distribution due to an inability to resolve their spheres of influence and/or megamasers may preferentially occur in lower-mass bhs. | megamaser disks reveal a broad distribution of black hole mass in spiral galaxies |
we present the lyman α flux power spectrum measurements of the xq-100 sample of quasar spectra obtained in the context of the european southern observatory large programme 'quasars and their absorption lines: a legacy survey of the high redshift universe with vlt/xshooter'. using 100 quasar spectra with medium resolution and signal-to-noise ratio, we measure the power spectrum over a range of redshifts z = 3-4.2 and over a range of scales k = 0.003-0.06 km-1 s. the results agree well with the measurements of the one-dimensional power spectrum found in the literature. the data analysis used in this paper is based on the fourier transform and has been tested on synthetic data. systematic and statistical uncertainties of our measurements are estimated, with a total error (statistical and systematic) comparable to the one of the boss data in the overlapping range of scales, and smaller by more than 50 per cent for higher redshift bins (z > 3.6) and small scales (k > 0.01 km-1 s). the xq-100 data set has the unique feature of having signal-to-noise ratios and resolution intermediate between the two data sets that are typically used to perform cosmological studies, i.e. boss and high-resolution spectra (e.g. uves/vlt or hires). more importantly, the measured flux power spectra span the high-redshift regime that is usually more constraining for structure formation models. | the lyman α forest power spectrum from the xq-100 legacy survey |
we present an analysis of uv spectra of 13 quasars believed to belong to extreme population a (xa) quasars, aimed at the estimation of the chemical abundances of the broad-line-emitting gas. metallicity estimates for the broad-line-emitting gas of quasars are subject to a number of caveats; xa sources with the strongest fe ii emission offer several advantages with respect to the quasar general population, as their optical and uv emission lines can be interpreted as the sum of a low-ionization component roughly at quasar rest frame (from virialized gas), plus a blueshifted excess (a disk wind), in different physical conditions. capitalizing on these results, we analyze the component at rest frame and the blueshifted one, exploiting the dependence of several intensity line ratios on metallicity z. we find that the validity of intensity line ratios as metallicity indicators depends on the physical conditions. we apply the measured diagnostic ratios to estimate the physical properties of sources such as density, ionization, and metallicity of the gas. our results confirm that the two regions (the low-ionization component and the blueshifted excess) of different dynamical conditions also show different physical conditions and suggest metallicity values that are high, and probably the highest along the quasar main sequence, with z ∼ 20-50 z⊙, if the solar abundance ratios can be assumed constant. we found some evidence of an overabundance of aluminum with respect to carbon, possibly due to selective enrichment of the broad-line-emitting gas by supernova ejecta. | high metal content of highly accreting quasars |
accreting black holes can drive fast and energetic nuclear winds that may be an important feedback mechanism associated with active galactic nuclei (agn). in this paper, we implement a scheme for capturing feedback from these fast nuclear winds and examine their impact in simulations of isolated disc galaxies. stellar feedback is modelled using the feedback in realistic environments (fire) physics and produces a realistic multiphase interstellar medium (ism). we find that agn winds drive the formation of a low-density, high-temperature central gas cavity that is broadly consistent with analytic model expectations. the effects of agn feedback on the host galaxy are a strong function of the wind kinetic power and momentum. low- and moderate-luminosity agn do not have a significant effect on their host galaxy: the agn winds inefficiently couple to the ambient ism and instead a significant fraction of their energy vents in the polar direction. for such massive black holes, accretion near the eddington limit can have a dramatic impact on the host galaxy ism: if agn wind feedback acts for ≳20-30 myr, the inner ~1-10 kpc of the ism is disrupted and the global galaxy star formation rate is significantly reduced. we quantify the properties of the resulting galaxy-scale outflows and find that the radial momentum in the outflow is boosted by a factor of ~2-3 relative to that initially supplied in the agn wind for strong feedback scenarios, decreasing below unity for less energetic winds. in contrast to observations, however, the outflows are primarily hot, with very little atomic or molecular gas. we conjecture that merging galaxies and high-redshift galaxies, which have more turbulent and thicker discs and very different nuclear gas geometries, may be even more disrupted by agn winds than found in our simulations. | the impact of agn wind feedback in simulations of isolated galaxies with a multiphase ism |
the extended baryon oscillation spectroscopic survey of the sloan digital sky survey (sdss-iv/eboss) has an extensive quasar program that combines several selection methods. among these, the photometric variability technique provides highly uniform samples, which are unaffected by the redshift bias of traditional optical-color selections, when z = 2.7-3.5 quasars cross the stellar locus or when host galaxy light affects quasar colors at z< 0.9. we present the variability selection of quasars in eboss, focusing on a specific program that led to a sample of 13 876 quasars to gdered = 22.5 over a 94.5 deg2 region in stripe 82, which has an areal density 1.5 times higher than over the rest of the eboss footprint. we use these variability-selected data to provide a new measurement of the quasar luminosity function (qlf) in the redshift range of 0.68 <z< 4.0. our sample is denser and reaches more deeply than those used in previous studies of the qlf, and it is among the largest ones. at the faint end, our qlf extends to mg(z = 2) = -21.80 at low redshift and to mg(z = 2) = -26.20 at z ~ 4. we fit the qlf using two independent double-power-law models with ten free parameters each. the first model is a pure luminosity-function evolution (ple) with bright-end and faint-end slopes allowed to be different on either side of z = 2.2. the other is a simple ple at z< 2.2, combined with a model that comprises both luminosity and density evolution (lede) at z> 2.2. both models are constrained to be continuous at z = 2.2. they present a flattening of the bright-end slope at high redshift. the lede model indicates a reduction of the break density with increasing redshift, but the evolution of the break magnitude depends on the parameterization. the models are in excellent accord, predicting quasar counts that agree within 0.3% (resp., 1.1%) to g< 22.5 (resp., g< 23). the models are also in good agreement over the entire redshift range with models from previous studies. | the extended baryon oscillation spectroscopic survey: variability selection and quasar luminosity function |
while low-mass, star-forming galaxies are often considered as the primary driver of reionization, their actual contribution to the cosmic ultraviolet background is still uncertain, mostly because the escape fraction of ionizing photons is only poorly constrained. theoretical studies have shown that efficient supernova feedback is a necessary condition to create paths through which ionizing radiation can escape into the intergalactic medium. we investigate the possibility that accreting supermassive black holes in early dwarf galaxies may provide additional feedback and enhance the leakage of ionizing radiation. we use a series of high-resolution cosmological radiation hydrodynamics simulations where we isolate the different sources of feedback. we find that supernova feedback prevents the growth of the black hole, thus quenching its associated feedback. even in cases where the black hole can grow, the structure of the interstellar medium is strongly dominated by supernova feedback. we conclude that, in the dwarf galaxy regime, supermassive black holes do not appear to play a significant role in enhancing the escape fraction and in contributing to the early ultraviolet background. | escape of ionizing radiation from high-redshift dwarf galaxies: role of agn feedback |
we investigate extremely red quasars (erqs), a remarkable population of heavily reddened quasars at redshift z ∼ 2-3 that might be caught during a short-lived `blow-out' phase of quasar/galaxy evolution. we perform a near-ir observational campaign using keck/nirspec, vlt/x-shooter, and gemini/gnirs to measure rest-frame optical spectra of 28 erqs with median infrared luminosity <log l(erg s-1)> ∼ 46.2. they exhibit the broadest and most blueshifted [o iii] λ4959,5007 emission lines ever reported, with widths (w90) ranging between 2053 and 7227 km s-1, and maximum outflow speeds (v98) up to 6702 km s-1. erqs on average have [o iii] outflows velocities about three times larger than those of luminosity-matched blue quasar samples. this discrepancy can be explained by a strong correlation between [o iii] kinematics and i-w3 colour, and not by radio loudness, or higher eddington ratios. we estimate for these objects that at least 3-5 per cent of their bolometric luminosity is being converted into the kinetic power of the observed wind. our results reveal that erqs have the potential to strongly affect the evolution of host galaxies. | erqs are the boss of quasar samples: the highest velocity [o iii] quasar outflows |
we present a science forecast for the extended baryon oscillation spectroscopic survey (eboss) survey. focusing on discrete tracers, we forecast the expected accuracy of the baryonic acoustic oscillation (bao), the redshift-space distortion (rsd) measurements, the fnl parameter quantifying the primordial non-gaussianity, the dark energy and modified gravity parameters. we also use the line-of-sight clustering in the lyman α forest to constrain the total neutrino mass. we find that eboss luminous red galaxies, emission line galaxies and clustering quasars can achieve a precision of 1, 2.2 and 1.6 per cent, respectively, for spherically averaged bao distance measurements. using the same samples, the constraint on fσ8 is expected to be 2.5, 3.3 and 2.8 per cent, respectively. for primordial non-gaussianity, eboss alone can reach an accuracy of σ(fnl) ∼ 10-15. eboss can at most improve the dark energy figure of merit by a factor of 3 for the chevallier-polarski-linder parametrization, and can well constrain three eigenmodes for the general equation-of-state parameter. eboss can also significantly improve constraints on modified gravity parameters by providing the rsd information, which is highly complementary to constraints obtained from weak lensing measurements. a principal component analysis shows that eboss can measure the eigenmodes of the effective newton's constant to 2 per cent precision; this is a factor of 10 improvement over that achievable without eboss. finally, we derive the eboss constraint (combined with planck, dark energy survey and boss) on the total neutrino mass, σ(σmν) = 0.03 ev (68 per cent cl), which in principle makes it possible to distinguish between the two scenarios of neutrino mass hierarchies. | the extended baryon oscillation spectroscopic survey: a cosmological forecast |
we report high spatial resolution (∼0.″076, 410 pc) atacama large millimeter/submillimeter array imaging of the dust continuum and the ionized carbon line [c ii] in a luminous quasar host galaxy at z = 6.6, 800 million years after the big bang. based on previous studies, this galaxy hosts a ∼1 × 109 {m}⊙black hole and has a star formation rate of ∼1500 {m}⊙yr-1. the unprecedented high resolution of the observations reveals a complex morphology of gas within 3 kpc of the accreting central black hole. the gas has a high velocity dispersion with little ordered motion along the line of sight, as would be expected from gas accretion that has yet to settle in a disk. in addition, we find the presence of [c ii] cavities in the gas distribution (with diameters of ∼0.5 kpc), offset from the central black hole. this unique distribution and kinematics cannot be explained by a simple model. plausible scenarios are that the gas is located in a truncated or warped disk, or the holes are created by interactions with nearby galaxies or due to energy injection into the gas. in the latter case, the energy required to form the cavities must originate from the central active galactic nucleus, as the required energy far exceeds the energy output expected from supernovae. this energy input into the gas, however, does not inhibit the high rate of star formation. both star formation and black hole activity could have been triggered by interactions with satellite galaxies; our data reveal three additional companions detected in [c ii] emission around the quasar. | 400 pc imaging of a massive quasar host galaxy at a redshift of 6.6 |
recently, the ligo-virgo collaboration (lvc) has concluded there is no evidence for lensed gravitational waves (gws) in the first half of the o3 run [ligo scientific collaboration and virgo collaboration, search for lensing signatures in the gravitational-wave observations from the first half of ligo-virgo's third observing run], claiming "we find the observation of lensed events to be unlikely, with the fractional rate at μ >2 being 3.3 ×10-4." while we agree that the chance of an individual gw event being lensed at μ >2 is smaller than <10-3, the number of observed events depends on the product of this small probability times the rate of mergers at high redshift. observational constraints from the stochastic gw background indicate that the rate of conventional mass binary black hole (bbh) mergers (8 <m /m⊙<15 ) in the redshift range 1 <z <2 could be as high as o(107) events per year, more than sufficient to compensate for the intrinsically low probability of lensing. to reach the lvc trigger threshold, these events require high magnification but would still produce up to 10-30 lvc observable events per year. thus, all the lvc observed ordinary stellar mass bbh mergers from this epoch must be strongly lensed with as many as 106 yr-1 events lying below the current detection threshold. by adopting a low bbh coalescence rate at high redshift, lvc implicitly assume that lensed events are insignificant and, thus, incorrectly underestimate the distances of most bbh events and correspondingly overestimate masses by factors of 2-5. furthermore, the lvc adopted priors on time delay for ideal circularly symmetric lenses are in tension with the known distribution of observed time delays of lensed quasars that require elliptical potentials with a broad spread of time delays. pairs of events like gw190421_213856gw190910_112807 and gw190424_180648gw190910_112807, which are directly assigned a probability of zero by lvc, should instead be considered as candidate lensed bbh pairs, since their separation in time is typical of lensed quasars. replacing the lvc model prior for the time delay distribution with the empirical quasar-based distribution reverses the lvc conclusions and says that a significant fraction of bbh pairs identified by lvc are viable multiply lensed events, including quadruple systems. | evidence for lensing of gravitational waves from ligo-virgo data |
we present the discovery of one or two extremely faint z ~ 6 quasars in 6.5 deg2 utilizing a unique capability of the wide-field imaging of the subaru/suprime-cam. the quasar selection was made in (i'-zb ) and (zb -zr ) colors, where zb and zr are bandpasses with central wavelengths of 8842 å and 9841 å, respectively. the color selection can effectively isolate quasars at z ~ 6 from m/l/t dwarfs without the j-band photometry down to zr < 24.0, which is 3.5 mag deeper than the sloan digital sky survey (sdss). we have selected 17 promising quasar candidates. the follow-up spectroscopy for seven targets identified one apparent quasar at z = 6.156 with m 1450 = -23.10. we also identified one possible quasar at z = 6.041 with a faint continuum of m 1450 = -22.58 and a narrow lyα emission with hwhm =427 km s-1, which cannot be distinguished from lyman α emitters. we derive the quasar luminosity function at z ~ 6 by combining our faint quasar sample with the bright quasar samples by sdss and cfhqs. including our data points invokes a higher number density in the faintest bin of the quasar luminosity function than the previous estimate employed. this suggests a steeper faint-end slope than lower z, though it is yet uncertain based on a small number of spectroscopically identified faint quasars, and several quasar candidates still remain to be diagnosed. the steepening of the quasar luminosity function at the faint end does increase the expected emission rate of the ionizing photon; however, it only changes by a factor of approximately two to six. this was found to still be insufficient for the required photon budget of reionization at z ~ 6. | the subaru high-z quasar survey: discovery of faint z ~ 6 quasars |
we present a systematic analysis of x-ray archival data of all the 29 quasars (qsos) at z> 5.5 observed so far with chandra, xmm-newton and swift-xrt, including the most-distant quasar ever discovered, ulas j1120+0641 (z = 7.08). this study allows us to place constraints on the mean spectral properties of the primordial population of luminous type 1 (unobscured) quasars. eighteen quasars are detected in the x-ray band, and we provide spectral-fitting results for their x-ray properties, while for the others we provide upper limits to their soft (0.5-2.0 kev) x-ray flux. we measured the power-law photon index and derived an upper limit to the column density for the five quasars (j1306+0356, j0100+2802, j1030+0524, j1148+5251, j1120+0641) with the best spectra (>30 net counts in the 0.5-7.0 kev energy range) and find that they are consistent with values from the literature and lower-redshift quasars. by stacking the spectra of ten quasars detected by chandra in the redshift range 5.7 ≤ z ≤ 6.1 we find a mean x-ray power-law photon index of γ = 1.92-0.27+0.28 and a neutral intrinsic absorption column density of nh ≤ 1023 cm-2. these results suggest that the x-ray spectral properties of luminous quasars have not evolved up to z ≈ 6. we also derived the optical-x-ray spectral slopes (αox) of our sample and combined them with those of previous works, confirming that αox strongly correlates with uv monochromatic luminosity at 2500 å. these results strengthen the non-evolutionary scenario for the spectral properties of luminous active galactic nuclei (agn). | the x-ray properties of z 6 luminous quasars |
the second data release of gaia revealed a parallax zero-point offset of −0.029 mas based on quasars. the value depended on the position on the sky, and also likely on magnitude and colour. the offset and its dependence on other parameters inhibited improvement in the local distance scale using for example the cepheid and rr lyrae period-luminosity relations. analysis of the recent gaia early data release 3 (edr3) reveals a mean parallax zero-point offset of −0.021 mas based on quasars. the gaia team addresses the parallax zero-point offset in detail and proposes a recipe to correct for it based on ecliptic latitude, g-band magnitude, and colour information. this paper presents a completely independent investigation into this issue focusing on the spatial dependence of the correction based on quasars and the magnitude dependence based on wide binaries. the spatial and magnitude corrections are connected to each other in the overlap region in the range 17 < g < 19. the spatial correction is presented at several spatial resolutions based on the healpix formalism. the colour dependence of the parallax offset is unclear and in any case secondary to the spatial and magnitude dependence. the spatial and magnitude corrections are applied to two samples of brighter sources, namely a sample of approximately 100 stars with independent trigonometric parallax measurements from hubble space telescope data, and a sample of 75 classical cepheids using photometric parallaxes. the mean offset between the observed gedr3 parallax and the independent trigonometric parallax (excluding outliers) is about −39 μas, and after applying the correction it is consistent with being zero. for the classical cepheid sample the analysis presented here suggests that the photometric parallaxes may be underestimated by about 5%. table 1 and full table 3 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/654/a20 | the parallax zero-point offset from gaia edr3 data |
we investigate the mean star formation rates (sfrs) in the host galaxies of ∼3000 optically selected quasi-stellar objects (qsos) from the sloan digital sky survey within the herschel-atlas fields, and a radio-luminous subsample covering the redshift range of z = 0.2-2.5. using wide-field infrared survey explorer (wise) and herschel photometry (12-500 μm) we construct composite spectral energy distributions (seds) in bins of redshift and active galactic nucleus (agn) luminosity. we perform sed fitting to measure the mean infrared luminosity due to star formation, removing the contamination from agn emission. we find that the mean sfrs show a weak positive trend with increasing agn luminosity. however, we demonstrate that the observed trend could be due to an increase in black hole (bh) mass (and a consequent increase of inferred stellar mass) with increasing agn luminosity. we compare to a sample of x-ray selected agn and find that the two populations have consistent mean sfrs when matched in agn luminosity and redshift. on the basis of the available virial bh masses, and the evolving bh mass to stellar mass relationship, we find that the mean sfrs of our qso sample are consistent with those of main sequence star-forming galaxies. similarly the radio-luminous qsos have mean sfrs that are consistent with both the overall qso sample and with star-forming galaxies on the main sequence. in conclusion, on average qsos reside on the main sequence of star-forming galaxies, and the observed positive trend between the mean sfrs and agn luminosity can be attributed to bh mass and redshift dependencies. | the mean star formation rates of unobscured qsos: searching for evidence of suppressed or enhanced star formation |
distortions of the observed cosmic microwave background provide a direct measurement of the microwave background temperature at redshifts from 0 to 1 (refs. 1,2). some additional background temperature estimates exist at redshifts from 1.8 to 3.3 based on molecular and atomic line-excitation temperatures in quasar absorption-line systems, but are model dependent3. no deviations from the expected (1 + z) scaling behaviour of the microwave background temperature have been seen4, but the measurements have not extended deeply into the matter-dominated era of the universe at redshifts z > 3.3. here we report observations of submillimetre line absorption from the water molecule against the cosmic microwave background at z = 6.34 in a massive starburst galaxy, corresponding to a lookback time of 12.8 billion years (ref. 5). radiative pumping of the upper level of the ground-state ortho-h2o(110-101) line due to starburst activity in the dusty galaxy hfls3 results in a cooling to below the redshifted microwave background temperature, after the transition is initially excited by the microwave background. this implies a microwave background temperature of 16.4-30.2 k (1σ range) at z = 6.34, which is consistent with a background temperature increase with redshift as expected from the standard λcdm cosmology4. | microwave background temperature at a redshift of 6.34 from h2o absorption |
a tight non-linear relation between the x-ray and the optical-ultraviolet (uv) emission has been observed in active galactic nuclei (agn) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence of an ubiquitous physical mechanism regulating the energy transfer between the accretion disc and the x-ray emitting corona. recently, our group developed a method to use this relation in observational cosmology, turning quasars into standardizable candles. this work mainly seeks to investigate the potential evolution of this correction at high redshifts. we thus studied the lx - luv relation for a sample of quasars in the redshift range 4 < z < 7, adopting the selection criteria proposed in our previous work regarding their spectral properties. the resulting sample consists of 53 type 1 (unobscured) quasars, observed either with chandra or xmm-newton, for which we performed a full spectral analysis, determining the rest-frame 2 kev flux density, as well as more general x-ray properties such as the estimate of photon index, and the soft (0.5-2 kev) and hard (2-10 kev) unabsorbed luminosities. we find that the relation shows no evidence for evolution with redshift. the intrinsic dispersion of the lx-luv for a sample free of systematics/contaminants is of the order of 0.22 dex, which is consistent with previous estimates from our group on quasars at lower redshift. | quasars as standard candles ii. the non-linear relation between uv and x-ray emission at high redshifts |
we report the results of 1.‧5 × 3‧ mapping at 1.1 mm with the atacama large millimeter/submillimeter array toward the central region of the z = 3.09 ssa22 protocluster. by combining our source catalog with archival spectroscopic redshifts, we find that eight submillimeter galaxies (smgs) with flux densities, s1.1 mm = 0.7-6.4 mjy (lir ∼ 1012.1-1013.1 l⊙) are at z = 3.08-3.10. not only are these smgs members of the protocluster, but they in fact reside within the node at the junction of the 50 mpc scale filamentary three-dimensional structure traced by lyα emitters in this field. the eight smgs account for a star formation rate density (sfrd) ∼10 m⊙ yr-1 mpc-3 in the node, which is two orders of magnitudes higher than the global sfrd at this redshift. we find that four of the eight smgs host an x-ray-luminous active galactic nucleus. our results suggest that the vigorous star formation activity and the growth of supermassive black holes (smbhs) occurred simultaneously in the densest regions at z ∼ 3, which may correspond to the most active historical phase of the massive galaxy population found in the core of the clusters in the present universe. two smgs are associated with lyα blobs, implying that the two populations coexist in high-density environments for a few cases. | alma deep field in ssa22: a concentration of dusty starbursts in a z = 3.09 protocluster core |
giant lobes of plasma extend ≈55° above and below the galactic center, glowing in emission from gamma rays (the fermi bubbles) to microwaves and polarized radio waves. we use ultraviolet absorption-line spectra from the hubble space telescope to constrain the velocity of the outflowing gas within these regions, targeting the quasar pds 456 (l, b = 10.°4, +11.°2). this sightline passes through a clear biconical structure seen in hard x-ray and gamma-ray emission near the base of the northern fermi bubble. we report two high-velocity metal absorption components, at v lsr = -235 and +250 km s-1, which cannot be explained by co-rotating gas in the galactic disk or halo. their velocities are suggestive of an origin on the front and back side of an expanding biconical outflow emanating from the galactic center. we develop simple kinematic biconical outflow models that can explain the observed profiles with an outflow velocity of gsim900 km s-1 and a full opening angle of ≈110° (matching the x-ray bicone). this indicates galactic center activity over the last ≈2.5-4.0 myr, in line with age estimates of the fermi bubbles. the observations illustrate the use of uv spectroscopy to probe the properties of swept-up gas venting into the fermi bubbles. based on observations taken under program 13448 of 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, and under program 14b-299 of the nrao green bank telescope, which is a facility of the national science foundation operated under cooperative agreement by associated universities, inc. | probing the fermi bubbles in ultraviolet absorption: a spectroscopic signature of the milky way's biconical nuclear outflow |
we performed a survey of the x-ray properties of 41 objects from the wise/sdss selected hyper-luminous (wissh) quasars sample, which includes 86 broad-line quasars with bolometric luminosity lbol ≳ 2 × 1047 erg s-1 shining at z 2-4. we used both proprietary and archival chandra and xmm-newton observations. twenty-one quasars have sufficient quality data to perform a spectroscopic analysis, while for the remaining sources, x-ray properties are derived through hardness-ratio analysis (apart for six sources that result to be undetected). the bulk ( 70%) of the detected wissh quasars exhibit nh <5 × 1022 cm-2, in agreement with their optical type 1 agn classification. all but three quasars show unabsorbed 2-10 kev luminosities l2-10≥ 1045 erg s-1. thanks to their extreme radiative output across the mid-ir-to-x-ray range, wissh quasars therefore offer the opportunity to significantly extend and validate the existing relations involving l2-10. specifically, we studied the x-ray luminosity as a function of (i) x-ray-to-optical (x/o) flux ratio; (ii) mid-ir luminosity (lmir); (iii) lbol, and (iv) αox versus 2500 å luminosity. we find that the wissh quasars show (i) unreported very low x/o ( <0.1) compared to typical agn values; (ii) l2-10/lmir ratios that are significantly smaller than those derived for agn with lower luminosity; (iii) a large x-ray bolometric correction, kbol,x ≈ 100-1000; and (iv) steep -2≳αox≳-1.7. these results lead to a scenario in which the x-ray emission of hyper-luminous quasars is relatively weaker compared to lower luminosity agn. models predict that such an x-ray weakness can be relevant for the acceleration of powerful high-ionization, emission-line-driven winds, which are commonly detected in the uv spectra of wissh quasars and can, in turn, perturb the x-ray corona and weaken its emission. accordingly, hyper-luminous quasars represent the ideal laboratory to study the link between the agn energy output and wind acceleration. additionally, wissh quasars exhibit very large smbh masses (log [mbh/m⊙]≳ 9.5). this enables a more robust modeling of the γ-mbh relation by increasing the statistics at high masses. we derive a flatter γ dependence than previously found over the broad range 5 ≲log (mbh/m⊙)≲ 11. finally, we estimate that only 300 ks observations of x-ifu on board athena will offer a detailed view of the properties of absorption features associated with powerful x-ray smbh winds for a representative sample of wissh quasars. | the wissh quasars project. iii. x-ray properties of hyper-luminous quasars |
we present alma band 3 observations of the co(6-5), co(7-6), and [c i] 369 μm emission lines in three of the highest-redshift quasar host galaxies at 6.6< z< 6.9. these measurements constitute the highest-redshift co detections to date. the target quasars have previously been detected in [c ii] 158 μm emission and the underlying fir dust continuum. we detect (spatially unresolved, at a resolution of >2″, or ≳14 kpc) co emission in all three quasar hosts. in two sources, we detect the continuum emission around 400 μm (rest-frame), and in one source we detect [c i] at low significance. we derive molecular gas reservoirs of (1-3) × 1010 {m}⊙in the quasar hosts, i.e., approximately only 10 times the mass of their central supermassive black holes. the extrapolated [c ii]-to-co(1-0) luminosity ratio is 2500-4200, consistent with measurements in galaxies at lower redshift. the detection of the [c i] line in one quasar host galaxy and the limit on the [c i] emission in the other two hosts enables a first characterization of the physical properties of the interstellar medium in z ∼ 7 quasar hosts. in the sources, the derived global co/[c ii]/[c i] line ratios are consistent with expectations from photodissociation regions, but not x-ray-dominated regions. this suggest that quantities derived from the molecular gas and dust emission are related to ongoing star-formation activity in the quasar hosts, providing further evidence that the quasar hosts studied here harbor intense starbursts in addition to their active nucleus. | molecular gas in three z ∼ 7 quasar host galaxies |
we develop a model of bose-einstein condensate dark matter halos with a solitonic core and an isothermal atmosphere based on a generalized gross-pitaevskii equation [p. h. chavanis, eur. phys. j. plus 132, 248 (2017), 10.1140/epjp/i2017-11544-3]. this equation provides a heuristic coarse-grained parametrization of the ordinary gross-pitaevskii equation accounting for violent relaxation and gravitational cooling. it involves a cubic nonlinearity taking into account the self-interaction of the bosons, a logarithmic nonlinearity associated with an effective temperature, and a source of dissipation. it leads to superfluid dark matter halos with a core-halo structure. the quantum potential or the self-interaction of the bosons generates a solitonic core that solves the cusp problem of the cold dark matter model. the logarithmic nonlinearity generates an isothermal atmosphere accounting for the flat rotation curves of the galaxies. the dissipation ensures that the system relaxes towards an equilibrium configuration. in the thomas-fermi approximation, a dark matter halo is equivalent to a barotropic gas with an equation of state p =2 π asℏ2ρ2/m3+ρ kbt /m , where as is the scattering length of the bosons and m is their individual mass. we numerically solve the equation of hydrostatic equilibrium and determine the density profiles and rotation curves of dark matter halos. we impose that the surface density of the halos has the universal value σ0=ρ0rh=141 m⊙/pc2 obtained from the observations. for a boson with ratio as/m3=3.28 ×103 fm /(ev / c2 )3 , we find a minimum halo mass (mh)min=1.86 ×108 m⊙ and a minimum halo radius (rh)min=788 pc . this ultracompact halo corresponds to a pure soliton which is the ground state of the gross-pitaevskii-poisson equation. for (mh)min<mh<(mh)*=3.30 ×109 m⊙ the soliton is surrounded by a tenuous isothermal atmosphere. for mh>(mh)*we find two branches of solutions corresponding to (i) purely isothermal halos without soliton and (ii) isothermal halos harboring a central soliton. the purely isothermal halos (gaseous phase) are stable. for mh>(mh)c=6.86 ×1010 m⊙ , they are indistinguishable from the observational burkert profile. for (mh)*<mh<(mh)c, the deviation from the isothermal law (most probable state) may be explained by incomplete violent relaxation, tidal effects, or stochastic forcing. the isothermal halos harboring a central soliton (core-halo phase) are canonically unstable (having a negative specific heat) but they are microcanonically stable so they are long-lived. by extremizing the free energy with respect to the core mass, we find that the core mass scales as mc/(mh)min=0.626 (mh/(mh)min)1 /2ln (mh/(mh)min) . for a halo of mass mh=1012 m⊙, similar to the mass of the dark matter halo that surrounds our galaxy, the solitonic core has a mass mc=6.39 ×1010 m⊙ and a radius rc=1 kpc . the solitonic core cannot mimic by itself a supermassive black hole at the center of the galaxy but it may represent a large bulge which is either present now or may have, in the past, triggered the collapse of the surrounding gas, leading to a supermassive black hole and a quasar. on the other hand, we argue that large halos with a mass mh>1012 m⊙ may undergo a gravothermal catastrophe leading ultimately to the formation of a supermassive black hole (for smaller halos, the gravothermal catastrophe is inhibited by quantum effects). we relate the bifurcation point and the point above which supermassive black holes may form to the canonical and microcanonical critical points (mh)ccp=3.27 ×109 m⊙ and (mh)mcp∼2 ×1012 m⊙ of the "thermal" self-gravitating bosonic gas. our model has no free parameter so it is completely predictive. extension of this model to noninteracting bosons and fermions will be presented in forthcoming papers. | predictive model of bec dark matter halos with a solitonic core and an isothermal atmosphere |
we describe the scientific goals and survey design of the first large absorption survey in h i (flash), a wide field survey for 21-cm line absorption in neutral atomic hydrogen (h i) at intermediate cosmological redshifts. flash will be carried out with the australian square kilometre array pathfinder (askap) radio telescope and is planned to cover the sky south of δ ≈ +40 ° at frequencies between 711.5 and 999.5 mhz. at redshifts between z = 0.4 and 1.0 (look-back times of 4 - 8 gyr), the h i content of the universe has been poorly explored due to the difficulty of carrying out radio surveys for faint 21-cm line emission and, at ultra-violet wavelengths, space-borne searches for damped lyman- α absorption in quasar spectra. the askap wide field of view and large spectral bandwidth, in combination with a radio-quiet site, will enable a search for absorption lines in the radio spectra of bright continuum sources over 80% of the sky. this survey is expected to detect at least several hundred intervening 21-cm absorbers and will produce an h i-absorption-selected catalogue of galaxies rich in cool, star-forming gas, some of which may be concealed from optical surveys. likewise, at least several hundred associated 21-cm absorbers are expected to be detected within the host galaxies of radio sources at 0.4 < z < 1.0, providing valuable kinematical information for models of gas accretion and jet-driven feedback in radio-loud active galactic nuclei. flash will also detect oh 18-cm absorbers in diffuse molecular gas, megamaser oh emission, radio recombination lines, and stacked h i emission. | the first large absorption survey in h i (flash): i. science goals and survey design |
the nature of dark matter is one of the most important unsolved questions in science. some darkf matter candidates do not have sufficient nongravitational interactions to be probed in laboratory or accelerator experiments. it is thus important to develop astrophysical probes which can constrain or lead to a discovery of such candidates. we illustrate this using state-of-the-art measurements of strong gravitationally lensed quasars to constrain four of the most popular sterile neutrino models, and also report the constraints for other independent methods that are comparable in procedure. first, we derive effective relations to describe the correspondence between the mass of a thermal relic warm dark matter particle and the mass of sterile neutrinos produced via higgs decay and grand unified theory (gut)-scale scenarios, in terms of large-scale structure and galaxy formation astrophysical effects. second, we show that sterile neutrinos produced through the higgs decay mechanism are allowed only for mass >26 kev , and gut-scale scenario >5.3 kev . third, we show that the single sterile neutrino model produced through active neutrino oscillations is allowed for mass >92 kev , and the three sterile neutrino minimal standard model (ν msm ) for mass >16 kev . these are the most stringent experimental limits on these models. | constraints on sterile neutrino models from strong gravitational lensing, milky way satellites, and the lyman-α forest |
we present a survey for metal absorption systems traced by neutral oxygen over 3.2 < z < 6.5. our survey uses keck/esi and vlt/x-shooter spectra of 199 qsos with redshifts up to 6.6. in total, we detect 74 o i absorbers, of which 57 are separated from the background qso by more than 5000 km s-1. we use a maximum likelihood approach to fit the distribution of o i λ1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with w 1302 > 0.05 å, of which there are 49 nonproximate systems in our sample. we find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. the number density over 4.9 < z < 5.7 is a factor of 1.7-4.1 lower (68% confidence) than that over 5.7 < z < 6.5, with a lower value at z < 5.7 favored with 99% confidence. this decrease suggests that the fraction of metals in a low-ionization phase is larger at z ∼ 6 than at lower redshifts. absorption from highly ionized metals traced by c iv is also weaker in higher-redshift o i systems, supporting this picture. the evolution of o i absorbers implies that metal-enriched circumgalactic gas at z ∼ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. this in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch. | the evolution of o i over 3.2 < z < 6.5: reionization of the circumgalactic medium |
the detection of two z ~ 13 galaxy candidates has opened a new window on galaxy formation at an era only 330 myr after the big bang. here, we investigate the physical nature of these sources: are we witnessing star forming galaxies or quasars at such early epochs? if powered by star formation, the observed ultraviolet (uv) luminosities and number densities can be jointly explained if: (i) these galaxies are extreme star-formers with star formation rates 5-24 × higher than those expected from extrapolations of average lower-redshift relations; (ii) the star formation efficiency increases with halo mass and is countered by increasing dust attenuation from z ~ 10-5; (iii) they form stars with an extremely top-heavy initial mass function. the quasar hypothesis is also plausible, with the uv luminosity produced by black holes of $\sim 10^8 \, \rm m_\odot$ accreting at or slightly above the eddington rate (fedd ~ 1.0). this black hole mass at z ~ 13 would require very challenging, but not implausible, growth parameters. if spectroscopically confirmed, these two sources will represent a remarkable laboratory to study the universe at previously inaccessible redshifts. | are the newly-discovered z 13 drop-out sources starburst galaxies or quasars? |
the filamentary network of intergalactic medium (igm) gas that gives origin to the lyα forest in the spectra of distant quasars encodes information on the physics of structure formation and the early thermodynamics of diffuse baryonic material. here we use a massive suite of more than 400 high-resolution cosmological hydrodynamical simulations run with the graphics processing unit-accelerated code cholla to study the igm at high spatial resolution maintained over the entire computational volume. the simulations capture a wide range of possible igm thermal histories by varying the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei. a statistical comparison of synthetic spectra with the observed 1d flux power spectra of hydrogen at redshifts 2.2 ≤ z ≤ 5.0 and with the helium lyα opacity at redshifts 2.4 < z < 2.9 tightly constrains the photoionization and photoheating history of the igm. by leveraging the constraining power of the available lyα forest data to break model degeneracies, we find that the igm experienced two main reheating events over 1.2 gyr of cosmic time. for our best-fit model, hydrogen reionization completes by zr≈ 6.0 with a first igm temperature peak of t 0 ≃ 1.3 × 104 k and is followed by the reionization of he ii that completes by z r ≈ 3.0 and yields a second temperature peak of t 0 ≃ 1.4 × 104 k. we discuss how our results can be used to obtain information on the timing and the sources of hydrogen and helium reionization. | inferring the thermal history of the intergalactic medium from the properties of the hydrogen and helium lyα forest |
we present a centennial review of the history of the term known as the cosmological constant. first introduced to the general theory of relativity by einstein in 1917 in order to describe a universe that was assumed to be static, the term fell from favour in the wake of the discovery of the expanding universe, only to make a dramatic return in recent times. we consider historical and philosophical aspects of the cosmological constant over four main epochs; (i) the use of the term in static cosmologies (both newtonian and relativistic): (ii) the marginalization of the term following the discovery of cosmic expansion: (iii) the use of the term to address specific cosmic puzzles such as the timespan of expansion, the formation of galaxies and the redshifts of the quasars: (iv) the re-emergence of the term in today's λ-cdm cosmology. we find that the cosmological constant was never truly banished from theoretical models of the universe, but was marginalized by astronomers for reasons of convenience. we also find that the return of the term to the forefront of modern cosmology did not occur as an abrupt paradigm shift due to one particular set of observations, but as the result of a number of empirical advances such as the measurement of present cosmic expansion using the hubble space telescope, the measurement of past expansion using type sn ia supernovae as standard candles, and the measurement of perturbations in the cosmic microwave background by balloon and satellite. we give a brief overview of contemporary interpretations of the physics underlying the cosmic constant and conclude with a synopsis of the famous cosmological constant problem. | one hundred years of the cosmological constant: from "superfluous stunt" to dark energy |
we investigate the observed correlation between the 2-10 kev x-ray luminosity (in unit of the eddington luminosity; lx ≡ lx/ledd) and the photon index (γ) of the x-ray spectrum for both black hole x-ray binaries (bhbs) and active galactic nuclei (agns). we construct a large sample, with 10- 9 ≲ lx ≲ 10- 1. we find that γ is positively and negatively correlated with lx when lx ≳ 10- 3 and 10- 6.5 ≲ lx ≲ 10- 3, respectively, while γ is nearly a constant when lx ≲ 10- 6.5. we explain the above correlation in the framework of a coupled hot accretion flow-jet model. the radio emission always comes from the jet while the x-ray emission comes from the accretion flow and jet when lx is above and below 10-6.5, respectively. more specifically, we assume that with the increase of mass accretion rate, the hot accretion flow develops into a clumpy and further a disc-corona two-phase structure because of thermal instability. we argue that such kind of two-phase accretion flow can explain the observed positive correlation. | correlation between the photon index and x-ray luminosity of black hole x-ray binaries and active galactic nuclei: observations and interpretation |
recent observations with alma have revealed evidence for nonthermal synchrotron emission from the core regions of two nearby seyfert galaxies. this suggests that the coronae of accretion disks in active galactic nuclei (agns) can be conducive to the acceleration of nonthermal electrons, in addition to the hot, thermal electrons responsible for their x-ray emission through thermal comptonization. here, we investigate the mechanism of such particle acceleration, based on observationally inferred parameters for agn disk coronae. one possibility to account for the observed nonthermal electrons is diffusive shock acceleration, as long as the gyrofactor ηgdoes not exceed ∼106. these nonthermal electrons can generate gamma-rays via inverse compton scattering of disk photons, which can appear in the mev band, while those with energies above ∼100 mev would be attenuated via internal γγ pair production. the integrated emission from all agns with thermal and nonthermal comptonization can reproduce the observed cosmic background radiation in x-rays as well as gamma-rays up to ∼10 mev. furthermore, if protons are accelerated in the same conditions as electrons and ηg∼ 30, our observationally motivated model is also able to account for the diffuse neutrino flux at energies below 100-300 tev. the next generation of mev gamma-ray and neutrino facilities can test these expectations by searching for signals from bright, nearby seyfert galaxies such as ngc 4151 and ic 4329a. | on high-energy particles in accretion disk coronae of supermassive black holes: implications for mev gamma-rays and high-energy neutrinos from agn cores |
we have started a long-term reverberation mapping (rm) project using the wyoming infrared observatory 2.3 m telescope titled “monitoring agns with hβ asymmetry” (maha). the motivations of the project are to explore the geometry and kinematics of the gas responsible for complex hβ emission-line profiles, ideally leading to an understanding of the structures and origins of the broad-line region (blr). furthermore, such a project provides the opportunity to search for evidence of close binary supermassive black holes. we describe maha and report initial results from our first campaign, from 2016 december to 2017 may, highlighting velocity-resolved time lags for four active galactic nuclei (agns) with asymmetric hβ lines. we find that 3c 120, ark 120, and mrk 6 display complex features different from the simple signatures expected for pure outflow, inflow, or a keplerian disk. while three of the objects have been previously reverberation mapped, including velocity-resolved time lags in the cases of 3c 120 and mrk 6, we report a time lag and corresponding black hole mass measurement for sbs 1518+593 for the first time. furthermore, sbs 1518+593, the least asymmetric of the four, does show velocity-resolved time lags characteristic of a keplerian disk or virialized motion more generally. also, the velocity-resolved time lags of 3c 120 have significantly changed since previously observed, indicating an evolution of its blr structure. future analyses of the data for these objects and others in maha will explore the full diversity of hβ lines and the physics of agn blrs. | monitoring agns with hβ asymmetry. i. first results: velocity-resolved reverberation mapping |
the supermassive black holes originally in the nuclei of two merging galaxies will form a binary in the remnant core. the early evolution of the massive binary is driven by dynamical friction before the binary becomes “hard” and eventually reaches coalescence through gravitational-wave emission. we consider the dynamical friction evolution of massive binaries consisting of a secondary hole orbiting inside a stellar cusp dominated by a more massive central black hole. in our treatment, we include the frictional force from stars moving faster than the inspiralling object, which is neglected in the standard chandrasekhar treatment. we show that the binary eccentricity increases if the stellar cusp density profile rises less steeply than ρ \propto {r}-2. in cusps shallower than ρ \propto {r}-1, the frictional timescale can become very long due to the deficit of stars moving slower than the massive body. although including fast stars increases the decay rate, low mass-ratio binaries (q≲ {10}-3) in sufficiently massive galaxies have decay timescales longer than one hubble time. during such minor mergers, the secondary hole stalls on an eccentric orbit at a distance of order one-tenth the influence radius of the primary hole (i.e., ≈ 10{--}100 {pc} for massive ellipticals). we calculate the expected number of stalled satellites as a function of the host galaxy mass and show that the brightest cluster galaxies should have ≳ 1 of such satellites orbiting within their cores. our results could provide an explanation for a number of observations, which include multiple nuclei in core ellipticals, off-center agns, and eccentric nuclear disks. | dynamical friction and the evolution of supermassive black hole binaries: the final hundred-parsec problem |
the rapid assembly of the massive black holes that power the luminous quasars observed at z ∼ 6-7 remains a puzzle. various direct collapse models have been proposed to head-start black hole growth from initial seeds with masses ∼105 m⊙, which can then reach a billion solar mass while accreting at the eddington limit. here, we propose an alternative scenario based on radiatively inefficient supercritical accretion of stellar-mass holes embedded in the gaseous circumnuclear discs (cnds) expected to exist in the cores of high-redshift galaxies. our sub-pc resolution hydrodynamical simulations show that stellar-mass holes orbiting within the central 100 pc of the cnd bind to very high density gas clumps that arise from the fragmentation of the surrounding gas. owing to the large reservoir of dense cold gas available, a stellar-mass black hole allowed to grow at super-eddington rates according to the `slim-disc' solution can increase its mass by three orders of magnitudes within a few million years. these findings are supported by simulations run with two different hydro codes, ramses based on the adaptive mesh refinement technique and gizmo based on a new lagrangian godunov-type method, and with similar, but not identical, sub-grid recipes for star formation, supernova feedback, black hole accretion and feedback. the low radiative efficiency of supercritical accretion flows are instrumental to the rapid mass growth of our black holes, as they imply modest radiative heating of the surrounding nuclear environment. | growing massive black holes through supercritical accretion of stellar-mass seeds |
we investigate the coevolution of galaxies and hosted supermassive black holes (bhs) throughout the history of the universe by a statistical approach based on the continuity equation and the abundance matching technique. specifically, we present analytical solutions of the continuity equation without source terms to reconstruct the supermassive bh mass function from the active galactic nucleus (agn) luminosity functions. such an approach includes physically motivated agn light curves tested on independent data sets, which describe the evolution of the eddington ratio and radiative efficiency from slim- to thin-disk conditions. we nicely reproduce the local estimates of the bh mass function, the agn duty cycle as a function of mass and redshift, along with the eddington ratio function and the fraction of galaxies with given stellar mass hosting an agn with given eddington ratio. we exploit the same approach to reconstruct the observed stellar mass function at different redshift from the ultraviolet and far-ir luminosity functions associated with star formation in galaxies. these results imply that the build-up of stars and bhs in galaxies occurs via in situ processes, with dry mergers playing a marginal role at least for stellar masses ≲ 3× {10}11 {m}⊙and bh masses ≲ {10}9 {m}⊙ , where the statistical data are more secure and less biased by systematic errors. in addition, we develop an improved abundance matching technique to link the stellar and bh content of galaxies to the gravitationally dominant dark matter (dm) component. the resulting relationships constitute a testbed for galaxy evolution models, highlighting the complementary role of stellar and agn feedback in the star formation process. in addition, they may be operationally implemented in numerical simulations to populate dm halos or to gauge subgrid physics. moreover, they may be exploited to investigate the galaxy/agn clustering as a function of redshift, mass, and/or luminosity. in fact, the clustering properties of bhs and galaxies are found to be in full agreement with current observations, thus further validating our results from the continuity equation. finally, our analysis highlights that (i) the fraction of agns observed in the slim-disk regime, where most of the bh mass is accreted, increases with redshift; and (ii) already at z≳ 6 a substantial amount of dust must have formed over timescales ≲ {10}8 yr in strongly star-forming galaxies, making these sources well within the reach of alma surveys in (sub)millimeter bands. | black hole and galaxy coevolution from continuity equation and abundance matching |
we present host stellar velocity dispersion measurements for a sample of 88 broad-line quasars at 0.1\lt z\lt 1 (46 at z\gt 0.6) from the sloan digital sky survey reverberation mapping (sdss-rm) project. high signal-to-noise ratio coadded spectra (average s/n≈ 30 per 69 km {{s}-1} pixel) from sdss-rm allowed for the decomposition of the host and quasar spectra and for measurements of the host stellar velocity dispersions and black hole (bh) masses using the single-epoch (se) virial method. the large sample size and dynamic range in luminosity ({{l}5100}={{10}43.2-44.7} erg {{s}-1}) lead to the first clear detection of a correlation between se virial bh mass and host stellar velocity dispersion far beyond the local universe. however, the observed correlation is significantly flatter than the local relation, suggesting that there are selection biases in high-z luminosity-threshold quasar samples for such studies. our uniform sample and analysis enable an investigation of the redshift evolution of the {{m}\bullet }-{{σ }*} relation relatively free of caveats by comparing different samples/analyses at disjoint redshifts. we do not observe evolution of the {{m}\bullet }-{{σ }*} relation in our sample up to z∼ 1, but there is an indication that the relation flattens toward higher redshifts. coupled with the increasing threshold luminosity with redshift in our sample, this again suggests that certain selection biases are at work, and simple simulations demonstrate that a constant {{m}\bullet }-{{σ }*} relation is favored to z∼ 1. our results highlight the scientific potential of deep coadded spectroscopy from quasar monitoring programs, and offer a new path to probe the co-evolution of bhs and galaxies at earlier times. | the sloan digital sky survey reverberation mapping project: no evidence for evolution in the m• -σ* relation to z∼ 1 |
we present deep (9 hr) gemini-n/gemini near-infrared spectrograph near-infrared spectroscopic observations of ulas j1342+0928, a luminous quasar at z = 7.54. various broad emission lines were detected, as well as the underlying continuum and iron forests over the rest-frame wavelength 970-2930 å. there is a clear trend that higher-ionization emission lines show larger blueshifts with c iv $\lambda 1549$ exhibiting ${5510}_{-110}^{+240}$ km s-1 blueshift with respect to the systematic redshift from the far-infrared [c ii] $158\,\mu {\rm{m}}$ emission line. those high-ionization lines have wide profiles with fwhm more than 10,000 km s-1. a modest blueshift of ${340}_{-80}^{+110}$ km s-1 is also seen in mg ii, the lowest-ionization line identified in the spectrum. the updated mg ii-based black hole mass of ${m}_{\mathrm{bh}}={9.1}_{-1.3}^{+1.4}\times {10}^{8}{m}_{\odot }$ and the eddington ratio of ${l}_{\mathrm{bol}}/{l}_{\mathrm{edd}}={1.1}_{-0.2}^{+0.2}$ confirm that ulas j1342+0928 is powered by a massive and actively accreting black hole. there is no significant difference in the emission-line ratios such as si iv/c iv and al iii/c iv when compared to lower-redshift quasars in a similar luminosity range, which suggests early metal pollution of the broad-line-region clouds. this trend also holds for the fe ii/mg ii line ratio, known as a cosmic clock that traces the iron enrichment in the early universe. different iron templates and continuum fitting ranges were used to explore how the fe ii/mg ii measurement changes as a function of spectral modeling. quasars at even higher redshift or at fainter luminosity range ( ${l}_{\mathrm{bol}}\lesssim {10}^{46}$ erg s-1) are needed to probe the sites of early metal enrichment and a corresponding change in the fe ii/mg ii ratio. | no redshift evolution in the broad-line-region metallicity up to z = 7.54: deep near-infrared spectroscopy of ulas j1342+0928 |
in this paper, based on a 2.29 ghz vlbi all-sky survey of 613 milliarcsecond ultra-compact radio sources with 0.0035<z<3.787, we describe a method of identifying the sub-sample which can serve as individual standard rulers in cosmology. if the linear size of the compact structure is assumed to depend on source luminosity and redshift as lm=l lβ (1+z)n, only intermediate-luminosity quasars (1027 w/hz<l< 1028 w/hz) show negligible dependence (|n|simeq 10-3, |β|simeq 10-4), and thus represent a population of such rulers with fixed characteristic length l=11.42 pc. with a sample of 120 such sources covering the redshift range 00.46<z<2.8, we confirm the existence of dark energy in the universe with high significance under the assumption of a flat universe, and obtain stringent constraints on both the matter density ωm=0.323+0.245-0.145 and the hubble constant h0=66.30+7.00-8.50 km sec-1 mpc-1. finally, with the angular diameter distances da measured for quasars extending to high redshifts (0z~ 3.), we reconstruct the da(z) function using the technique of gaussian processes. this allows us to identify the redshift corresponding to the maximum of the da(z) function: 0zm=1.7 and the corresponding angular diameter distance da(zm)=1719.01±43.46 mpc. similar reconstruction of the expansion rate function h(z) based on the data from cosmic chronometers and bao gives us h(zm)=176.77±6.11 km sec-1 mpc-1. these measurements are used to estimate the speed of light: c=3.039(±0.180)× 105 km/s. this is the first measurement of the speed of light in a cosmological setting referring to the distant past. | measuring the speed of light with ultra-compact radio quasars |
the multiwavelength spectral and temporal variability observed in blazars set tight constraints on current theoretical emission models. here, we investigate the relativistic magnetic reconnection process as a source of blazar emission in which quasi-spherical plasmoids, containing relativistic particles and magnetic fields, are associated with the emission sites in blazar jets. by coupling recent two-dimensional particle-in-cell simulations of relativistic reconnection with a time-dependent radiative transfer code, we compute the non-thermal emission from a chain of plasmoids formed during a reconnection event. the derived photon spectra display characteristic features observed in both bl lac sources and flat spectrum radio quasars, with the distinction made by varying the strength of the external photon fields, the jet magnetization, and the number of pairs per proton contained within. light curves produced from reconnection events are composed of many fast and powerful flares that appear on excess of a slower evolving envelope produced by the cumulative emission of medium-sized plasmoids. the observed variability is highly dependent upon the orientation of the reconnection layer with respect to the blazar jet axis and to the observer. our model provides a physically motivated framework for explaining the multitime-scale blazar variability across the entire electromagnetic spectrum. | radiative signatures of plasmoid-dominated reconnection in blazar jets |
a major goal of the atacama large millimeter/submillimeter array (alma) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. to develop and test this capability, a long baseline campaign (lbc) was carried out from 2014 september to late november, culminating in end-to-end observations, calibrations, and imaging of selected science verification (sv) targets. this paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the alma site, a summary of the sv targets and observations, and recommendations for science observing strategies at long baselines. deep alma images of the quasar 3c 138 at 97 and 241 ghz are also compared to vla 43 ghz results, demonstrating an agreement at a level of a few percent. as a result of the extensive program of lbc testing, the highly successful sv imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 ghz. observing with alma on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy. . | the 2014 alma long baseline campaign: an overview |
given a galaxy's stellar mass, its host halo mass has a lower limit from the cosmic baryon fraction and known baryonic physics. at z> 4, galaxy stellar mass functions place lower limits on halo number densities that approach expected lambda cold dark matter halo mass functions. high-redshift galaxy stellar mass functions can thus place interesting limits on number densities of massive haloes, which are otherwise very difficult to measure. although halo mass functions at z < 8 are consistent with observed galaxy stellar masses if galaxy baryonic conversion efficiencies increase with redshift, jwst(james webb space telescope) and wfirst(wide-field infrared survey telescope) will more than double the redshift range over which useful constraints are available. we calculate maximum galaxy stellar masses as a function of redshift given expected halo number densities from λcdm. we apply similar arguments to black holes. if their virial mass estimates are accurate, number density constraints alone suggest that the quasars sdss j1044-0125 and sdss j010013.02+280225.8 likely have black hole mass to stellar mass ratios higher than the median z = 0 relation, confirming the expectation from lauer bias. finally, we present a public code to evaluate the probability of an apparently λcdm-inconsistent high-mass halo being detected given the combined effects of multiple surveys and observational errors. | the most massive galaxies and black holes allowed by λcdm |
we present a study exploring the nature and properties of the circumgalactic medium (cgm) and its connection to the atomic gas content in the interstellar medium (ism) of galaxies as traced by the h i 21 cm line. our sample includes 45 low-z (0.026-0.049) galaxies from the galex arecibo sdss survey (galaxy evolution explorer/arecibo/sloan digital sky survey). their cgm was probed via absorption in the spectra of background quasi-stellar objects at impact parameters of 63-231 kpc. the spectra were obtained with the cosmic origins spectrograph aboard the hubble space telescope. we detected neutral hydrogen (lyα absorption lines) in the cgm of 92% of the galaxies. we find that the radial profile of the cgm as traced by the lyα equivalent width can be fit as an exponential with a scale length of roughly the virial radius of the dark matter halo. we found no correlation between the orientation of the sightline relative to the galaxy’s major axis and the lyα equivalent width. the velocity spread of the circumgalactic gas is consistent with that seen in the atomic gas in the ism. we find a strong correlation (99.8% confidence) between the gas fraction (m(h i)/m⋆) and the impact-parameter-corrected lyα equivalent width. this is stronger than the analogous correlation between corrected lyα equivalent width and specific star formation rate (sfr)/m⋆ (97.5% confidence). these results imply a physical connection between the h i disk and the cgm, which is on scales an order of magnitude larger. this is consistent with the picture in which the h i disk is nourished by accretion of gas from the cgm. | connection between the circumgalactic medium and the interstellar medium of galaxies: results from the cos-gass survey |
using chandra observations in the 2.15 deg2 cosmos-legacy field, we present one of the most accurate measurements of the cosmic x-ray background (cxb) spectrum to date in the [0.3-7] kev energy band. the cxb has three distinct components: contributions from two galactic collisional thermal plasmas at kt ∼ 0.27 and 0.07 kev and an extragalactic power law with a photon spectral index γ = 1.45 ± 0.02. the 1 kev normalization of the extragalactic component is 10.91 ± 0.16 kev cm-2 s-1 sr-1 kev-1. removing all x-ray-detected sources, the remaining unresolved cxb is best fit by a power law with normalization 4.18 ± 0.26 kev cm-2 s-1 sr-1 kev-1 and photon spectral index γ = 1.57 ± 0.10. removing faint galaxies down to {i}{ab}∼ 27{--}28 leaves a hard spectrum with {{γ }}∼ 1.25 and a 1 kev normalization of ∼1.37 kev cm-2 s-1 sr-1 kev-1. this means that ∼91% of the observed cxb is resolved into detected x-ray sources and undetected galaxies. unresolved sources that contribute ∼8%-9% of the total cxb show marginal evidence of being harder and possibly more obscured than resolved sources. another ∼1% of the cxb can be attributed to still undetected star-forming galaxies and absorbed active galactic nuclei. according to these limits, we investigate a scenario where early black holes totally account for non-source cxb fraction and constrain some of their properties. in order to not exceed the remaining cxb and the z∼ 6 accreted mass density, such a population of black holes must grow in compton-thick envelopes with {n}h > 1.6 × 1025 cm-2 and form in extremely low-metallicity environments ({z}⊙ )∼ {10}-3. | the chandra cosmos legacy survey: energy spectrum of the cosmic x-ray background and constraints on undetected populations |
we present the first results from the quasar feedback survey, a sample of 42 z < 0.2, [o iii] luminous agns ( l[o iii] > 1042.1 ergs s-1) with moderate radio luminosities (i.e. l1.4ghz > 1023.4 w hz-1; median l1.4ghz = 5.9 × 1023 w hz-1). using high spatial resolution (~0.3-1 arcsec), 1.5-6 ghz radio images from the very large array, we find that 67 per cent of the sample have spatially extended radio features on ~1-60 kpc scales. the radio sizes and morphologies suggest that these may be lower radio luminosity versions of compact, radio-loud agns. by combining the radio-to-infrared excess parameter, spectral index, radio morphology, and brightness temperature, we find radio emission in at least 57 per cent of the sample that is associated with agn-related processes (e.g. jets, quasar-driven winds, or coronal emission). this is despite only 9.5-21 per cent being classified as radio-loud using traditional criteria. the origin of the radio emission in the remainder of the sample is unclear. we find that both the established anticorrelation between radio size and the width of the [o iii] line, and the known trend for the most [o iii] luminous agns to be associated with spatially extended radio emission, also hold for our sample of moderate radio luminosity quasars. these observations add to the growing evidence of a connection between the radio emission and ionized gas in quasar host galaxies. this work lays the foundation for deeper investigations into the drivers and impact of feedback in this unique sample. | the quasar feedback survey: discovering hidden radio-agn and their connection to the host galaxy ionized gas |
we revisit the dependence of the covering factor (cf) of dust torus on physical properties of active galactic nuclei (agns) by taking into account an agn polar dust emission. the cf is converted from a ratio of infrared (ir) luminosity contributed from agn dust torus ( ${l}_{\mathrm{ir}}^{\mathrm{torus}}$ ) and agn bolometric luminosity (lbol), by assuming a nonlinear relation between luminosity ratio and intrinsic cf. we select 37,181 type 1 quasars at z < 0.7 from the sloan digital sky survey data release 16 quasar catalog. their lbol, black hole mass (mbh), and eddington ratio (λedd) are derived by spectral fitting with qsfit. we conduct spectral energy distribution decomposition by using x-cigale with a clumpy torus and polar dust model to estimate ${l}_{\mathrm{ir}}^{\mathrm{torus}}$ without being affected by the contribution of stellar and agn polar dust to ir emission. for 5752 quasars whose physical quantities are securely determined, we perform a correlation analysis on cf and (i) lbol, (ii) mbh, and (iii) λedd. as a result, anticorrelations for cf-lbol, cf-mbh, and cf-λedd are confirmed. we find that incorporating the agn polar dust emission makes those anticorrelations stronger compared to those without considering it. this indicates that polar dust wind probably driven by agn radiative pressure is one of the key components to regulate obscuring material of agns. | how does the polar dust affect the correlation between dust covering factor and eddington ratio in type 1 quasars selected from the sloan digital sky survey data release 16? |
we consider the cosmological consequences if a small fraction (f≲ 0.1) of the dark matter is ultra-strongly self-interacting, with an elastic self-interaction cross section per unit mass σ \gg 1 c{{m}2} {{g}-1}. this possibility evades all current constraints that assume that the self-interacting component makes up the majority of the dark matter. nevertheless, even a small fraction of ultra-strongly self-interacting dark matter (usidm) can have observable consequences on astrophysical scales. in particular, the usidm subcomponent can undergo gravothermal collapse and form seed black holes in the center of a halo. these seed black holes, which form within several hundred halo interaction times, contain a few percent of the total usidm mass in the halo. for reasonable values of σ f, these black holes can form at high enough redshifts to grow to ∼ {{10}9} {{m}⊙ } quasars by z≳ 6, alleviating tension within the standard λ cold dark matter cosmology. the ubiquitous formation of central black holes in halos could also create cores in dwarf galaxies by ejecting matter during binary black hole mergers, potentially resolving the “too big to fail” problem. | supermassive black holes from ultra-strongly self-interacting dark matter |
dust plays an important role in our understanding of the universe, but it is not obvious yet how the dust in the distant universe was formed. i derived the dust yields per asymptotic giant branch (agb) star and per supernova (sn) required to explain dust masses of galaxies at z = 6.3-7.5 (680-850 million years after the big bang) for which dust emission has been detected (hfls3 at z = 6.34, ulas j1120+0641 at z = 7.085, and a1689-zd1 at z = 7.5), or unsuccessfully searched for. i found very high required yields, implying that agb stars could not contribute substantially to dust production at these redshifts, and that sne could explain these dust masses, but only if they do not destroy most of the dust they form (which is unlikely given the upper limits on the sn dust yields derived for galaxies where dust is not detected). this suggests that the grain growth in the interstellar medium is likely required at these early epochs. | dust production 680-850 million years after the big bang |
black hole masses are crucial to understanding the physics of the connection between quasars and their host galaxies and measuring cosmic black hole-growth. at high redshift, z ≳ 2.1, black hole masses are normally derived using the velocity width of the c iv λ λ1548, 1550 broad emission line, based on the assumption that the observed velocity widths arise from virial-induced motions. in many quasars, the c iv emission line exhibits significant blue asymmetries (`blueshifts') with the line centroid displaced by up to thousands of km s-1 to the blue. these blueshifts almost certainly signal the presence of strong outflows, most likely originating in a disc wind. we have obtained near-infrared spectra, including the hα λ6565 emission line, for 19 luminous (lbol = 46.5-47.5 erg s-1) sloan digital sky survey quasars, at redshifts 2 < z < 2.7, with c iv emission lines spanning the full range of blueshifts present in the population. a strong correlation between c iv velocity width and blueshift is found and, at large blueshifts, >2000 km s-1, the velocity widths appear to be dominated by non-virial motions. black hole masses, based on the full width at half-maximum of the c iv emission line, can be overestimated by a factor of 5 at large blueshifts. a larger sample of quasar spectra with both c iv and h β, or hα, emission lines will allow quantitative corrections to c iv-based black hole masses as a function of blueshift to be derived. we find that quasars with large c iv blueshifts possess high eddington luminosity ratios and that the fraction of high-blueshift quasars in a flux-limited sample is enhanced by a factor of approximately 4 relative to a sample limited by black hole mass. | c iv emission-line properties and systematic trends in quasar black hole mass estimates |
the advent of time domain astronomy is revolutionizing our understanding of the universe. programs such as the catalina real-time transient survey (crts) or the palomar transient factory (ptf) surveyed millions of objects for several years, allowing variability studies on large statistical samples. the inspection of ≈250 k quasars in crts resulted in a catalog of 111 potentially periodic sources, put forward as supermassive black hole binary (smbhb) candidates. a similar investigation on ptf data yielded 33 candidates from a sample of ≈35 k quasars. working under the smbhb hypothesis, we compute the implied smbhb merger rate and we use it to construct the expected gravitational wave background (gwb) at nano-hz frequencies, probed by pulsar timing arrays (ptas). after correcting for incompleteness and assuming virial mass estimates, we find that the gwb implied by the crts sample exceeds the current most stringent pta upper limits by almost an order of magnitude. after further correcting for the implicit bias in virial mass measurements, the implied gwb drops significantly but is still in tension with the most stringent pta upper limits. similar results hold for the ptf sample. bayesian model selection shows that the null hypothesis (whereby the candidates are false positives) is preferred over the binary hypothesis at about 2.3σ and 3.6σ for the crts and ptf samples respectively. although not decisive, our analysis highlights the potential of ptas as astrophysical probes of individual smbhb candidates and indicates that the crts and ptf samples are likely contaminated by several false positives. | testing the binary hypothesis: pulsar timing constraints on supermassive black hole binary candidates |
using few-body simulations, we investigate the evolution of supermassive black holes (smbhs) in galaxies (m* = 1010-1012 m⊙ at z = 0) at 0 < z < 4. following galaxy merger trees from the millennium simulation, we model bh mergers with two extreme binary decay scenarios for the 'hard binary' stage: a full or an empty loss cone. these two models should bracket the true evolution, and allow us to separately explore the role of dynamical friction and that of multibody bh interactions on bh mergers. using the computed merger rates, we infer the stochastic gravitational wave background (gwb). our dynamical approach is a first attempt to study the dynamical evolution of multiple smbhs in the host galaxies undergoing mergers with various mass ratios (10-4 < q* < 1). our main result demonstrates that smbh binaries are able to merge in both scenarios. in the empty loss cone case, we find that bhs merge via multibody interactions, avoiding the 'final parsec' problem, and entering the pulsar timing arrays band with substantial orbital eccentricity. our full loss cone treatment, albeit more approximate, suggests that the eccentricity becomes even higher when gws become dominant, leading to rapid coalescences (binary lifetime ≲1 gyr). despite the lower merger rates in the empty loss cone case, due to their higher mass ratios and lower redshifts, the gwb in the full/empty loss cone models are comparable (0.70 × 10-15 and 0.53 × 10-15 at a frequency of 1 yr-1, respectively). finally, we compute the effects of high eccentricities on the gwb spectrum. | interactions between multiple supermassive black holes in galactic nuclei: a solution to the final parsec problem |
this is the eighth in a series of papers reporting on a large reverberation mapping (rm) campaign to measure black hole (bh) mass in active galactic nuclei with high accretion rates. we employ the recently developed dynamical modeling approach for broad-line regions (blrs) based on the method of pancoast et al. to analyze the rm data set of mrk 142 observed in the first monitoring season. in this approach, continuum variations are reconstructed using a damped random walk process, and blr structure is delineated using a flexible disk-like geometry, in which blr clouds move around the central bh with keplerian orbits or inflow/outflow motion. the approach also includes the possibilities of anisotropic emission from blr clouds, nonlinear response of the line emission to the continuum, and different long-term trends in the continuum and emission-line variations. we implement the approach in a bayesian framework that is apt for parallel computation and use a markov chain monte carlo technique to recover the parameters and uncertainties for the modeling, including the mass of the central bh. we apply three blr models with different prescriptions of blr cloud distributions and find that the best model for fitting the data of mrk 142 is a two-zone blr model, consistent with the theoretical blr model surrounding slim accretion disks. the best model yields a bh mass of {log}({m}\bullet /{m}⊙ )={6.23}-0.45+0.26, resulting in a virial factor of {log}f=-{0.36}-0.54+0.33 for the full width at half maximum of the hβ line measured from the mean spectrum. the virial factors for the other measures of the hβ line width are also presented. | supermassive black holes with high accretion rates in active galactic nuclei. viii. structure of the broad-line region and mass of the central black hole in mrk 142 |
cmb lensing tomography, or the cross-correlation between cmb lensing maps and large-scale structure tracers over a well-defined redshift range, has the potential to map the amplitude and growth of structure over cosmic time, provide some of the most stringent tests of gravity, and break important degeneracies between cosmological parameters. in this work, we use the unwise galaxy catalog to provide three samples at median redshifts z ~ 0.6, 1.1 and 1.5, fully spanning the dark energy dominated era, together with the most recent planck cmb lensing maps. we obtain a combined cross-correlation significance s/n = 79.3 over the range of scales 100 < l < 1000. we measure the redshift distribution of unwise sources by a combination of cross-matching with the cosmos photometric catalog and cross-correlation with boss galaxies and quasars and eboss quasars. we also show that magnification bias must be included in our analysis and perform a number of null tests. in a companion paper, we explore the derived cosmological parameters by modeling the non-linearities and propagating the redshift distribution uncertainties. | unwise tomography of planck cmb lensing |
we present a study of optical, uv and x-ray light curves of the nearby changing look active galactic nucleus in the galaxy ngc 1566 obtained with the neil gehrels swift observatory and the master global robotic network over the period 2007-2018. we also report on our optical spectroscopy at the south african astronomical observatory with the 1.9-m telescope on the night 2018 august 2-3. a substantial increase in x-ray flux by 1.5 orders of magnitude was observed following the brightening in the uv and optical bands during the last year. after a maximum was reached at the beginning of 2018 july the fluxes in all bands decreased with some fluctuations. the amplitude of the flux variability is strongest in the x-ray band and decreases with increasing wavelength. low-resolution spectra reveal a dramatic strengthening of the broad emission as well as high-ionization [fe x]6374 å lines. these lines were not detected so strongly in the past published spectra. the change in the type of the optical spectrum was accompanied by a significant change in the x-ray spectrum. all these facts confirm ngc 1566 to be a changing look seyfert galaxy. | new changing look case in ngc 1566 |
we have recently identified a substantial number of type 1 active galactic nuclei (agns) featuring weak broad-line regions (blrs) at z\lt 0.2 from detailed analysis of galaxy spectra in the sloan digital sky survey data release 7. these objects predominantly show a stellar continuum but also a broad hα emission line, indicating the presence of a low-luminosity agn oriented so that we are viewing the central engine directly without significant obscuration. these accreting black holes have previously eluded detection due to their weak nature. the newly discovered blr agns have increased the number of known type 1 agns by 49%. some of these new blr agns were detected with the chandra x-ray observatory, and their x-ray properties confirm that they are indeed type 1 agns. based on our new and more complete catalog of type 1 agns, we derived the type 1 fraction of agns as a function of [o iii] λ 5007 emission luminosity and explored the possible dilution effect on obscured agns due to star formation. the new type 1 agn fraction shows much more complex behavior with respect to black hole mass and bolometric luminosity than has been suggested previously by the existing receding torus model. the type 1 agn fraction is sensitive to both of these factors, and there seems to be a sweet spot (ridge) in the diagram of black hole mass and bolometric luminosity. furthermore, we present the possibility that the eddington ratio plays a role in determining opening angles. | a new catalog of type 1 agns and its implications on the agn unified model |
the current hierarchical merging paradigm and λcdm predict that the z∼ 4-8 universe should be a time in which the most massive galaxies are transitioning from their initial halo assembly to the later baryonic evolution seen in star-forming galaxies and quasars. however, no evidence of this transition has been found in many high-redshift galaxy surveys including cfhtls, cosmic assembly near-infrared deep extragalactic survey (candels), and spitzer large area survey with hyper-suprime-cam (splash), which were the first studies to probe the high-mass end at these redshifts. indeed, if halo mass to stellar mass ratios estimated at lower-redshift continue to z∼ 6-8, candels and splash report several orders of magnitude more m∼ {10}12-13{m}⊙halos than is possible to have been formed by those redshifts, implying that these massive galaxies formed impossibly early. we consider various systematics in the stellar synthesis models used to estimate physical parameters and possible galaxy formation scenarios in an effort to reconcile observation with theory. although known uncertainties can greatly reduce the disparity between recent observations and cold dark matter merger simulations, there remains considerable tension with current theory even if taking the most conservative view of the observations. | the impossibly early galaxy problem |
radio emission from radio-quiet quasars may be due to star formation in the quasar host galaxy, to a jet launched by the supermassive black hole, or to relativistic particles accelerated in a wide-angle radiatively driven outflow. in this paper, we examine whether radio emission from radio-quiet quasars is a byproduct of star formation in their hosts. to this end, we use infrared spectroscopy and photometry from spitzer and herschel to estimate or place upper limits on star formation rates in hosts of ∼300 obscured and unobscured quasars at z < 1. we find that low-ionization forbidden emission lines such as [ne ii] and [ne iii] are likely dominated by quasar ionization and do not provide reliable star formation diagnostics in quasar hosts, while polycyclic aromatic hydrocarbon (pah) emission features may be suppressed due to the destruction of pah molecules by the quasar radiation field. while the bolometric luminosities of our sources are dominated by the quasars, the 160 μm fluxes are likely dominated by star formation, but they too should be used with caution. we estimate median star formation rates to be 6-29 m⊙ yr-1, with obscured quasars at the high end of this range. this star formation rate is insufficient to explain the observed radio emission from quasars by an order of magnitude, with log (lradio, obs/lradio, sf) = 0.6-1.3 depending on quasar type and star formation estimator. although radio-quiet quasars in our sample lie close to the 8-1000 μm infrared/radio correlation characteristic of the star-forming galaxies, both their infrared emission and their radio emission are dominated by the quasar activity, not by the host galaxy. | star formation in quasar hosts and the origin of radio emission in radio-quiet quasars |
mse is an 11.25m aperture observatory with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. more than 3200 fibres will feed spectrographs operating at low (r ~ 2000 - 3500) and moderate (r ~ 6000) spectral resolution, and approximately 1000 fibers will feed spectrographs operating at high (r ~ 40000) resolution. mse is designed to enable transformational science in areas as diverse as tomographic mapping of the interstellar and intergalactic media; the in-situ chemical tagging of thick disk and halo stars; connecting galaxies to their large scale structure; measuring the mass functions of cold dark matter sub-halos in galaxy and cluster-scale hosts; reverberation mapping of supermassive black holes in quasars; next generation cosmological surveys using redshift space distortions and peculiar velocities. mse is an essential follow-up facility to current and next generations of multi-wavelength imaging surveys, including lsst, gaia, euclid, wfirst, plato, and the ska, and is designed to complement and go beyond the science goals of other planned and current spectroscopic capabilities like vista/4most, wht/weave, aat/hermes and subaru/pfs. it is an ideal feeder facility for e-elt, tmt and gmt, and provides the missing link between wide field imaging and small field precision astronomy. mse is optimized for high throughput, high signal-to-noise observations of the faintest sources in the universe with high quality calibration and stability being ensured through the dedicated operational mode of the observatory. (abridged) | the detailed science case for the maunakea spectroscopic explorer: the composition and dynamics of the faint universe |
the circumgalactic medium (cgm) encodes signatures of the galaxy-formation process, including the interaction of galactic outflows driven by stellar and supermassive black hole (smbh) feedback with the gaseous halo. moving beyond spherically symmetric radial profiles, we study the angular dependence of cgm properties around z = 0 massive galaxies in the illustristng simulations. we characterize the angular signal of density, temperature, and metallicity of the cgm as a function of galaxy stellar mass, halo mass, distance, and smbh mass, via stacking. tng predicts that the cgm is anisotropic in its thermodynamical properties and chemical content over a large mass range, $m_*\sim 10^{10-11.5}\, \mathrm{m}_\odot$. along the minor axis directions, gas density is diluted, whereas temperature and metallicity are enhanced. these feedback-induced anisotropies in the cgm have a magnitude of 0.1-0.3 dex, extend out to the halo virial radius, and peak at milky way-like masses, $m_*\sim 10^{10.8}\, \mathrm{m}_\odot$. in tng, this mass scale corresponds to the onset of efficient smbh feedback and the production of strong outflows. by comparing the anisotropic signals predicted by tng versus other simulations - illustris and eagle - we find that each simulation produces distinct signatures and mass dependencies, implying that this phenomenon is sensitive to the underlying physical models. finally, we explore x-ray emission as an observable of this cgm anisotropy, finding that future x-ray observations, including the erosita all-sky survey, will be able to detect and characterize this signal, particularly in terms of an angular modulation of the x-ray hardness. | predictions for anisotropic x-ray signatures in the circumgalactic medium: imprints of supermassive black hole driven outflows |
we investigate the large-scale clustering of the final spectroscopic sample of quasars from the recently completed extended baryon oscillation spectroscopic survey (eboss). the sample contains 343 708 objects in the redshift range 0.8 < z < 2.2 and 72 667 objects with redshifts 2.2 < z < 3.5, covering an effective area of $4699\, {\rm deg}^{2}$. we develop a neural network-based approach to mitigate spurious fluctuations in the density field caused by spatial variations in the quality of the imaging data used to select targets for follow-up spectroscopy. simulations are used with the same angular and radial distributions as the real data to estimate covariance matrices, perform error analyses, and assess residual systematic uncertainties. we measure the mean density contrast and cross-correlations of the eboss quasars against maps of potential sources of imaging systematics to address algorithm effectiveness, finding that the neural network-based approach outperforms standard linear regression. stellar density is one of the most important sources of spurious fluctuations, and a new template constructed using data from the gaia spacecraft provides the best match to the observed quasar clustering. the end-product from this work is a new value-added quasar catalogue with the improved weights to correct for non-linear imaging systematic effects, which will be made public. our quasar catalogue is used to measure the local-type primordial non-gaussianity in a companion paper. | primordial non-gaussianity from the completed sdss-iv extended baryon oscillation spectroscopic survey - i: catalogue preparation and systematic mitigation |
we study the distribution and evolution of highly ionized intergalactic metals in the evolution and assembly of galaxies and their environment (eagle) cosmological, hydrodynamical simulations. eagle has been shown to reproduce a wide range of galaxy properties while its subgrid feedback was calibrated without considering gas properties. we compare the predictions for the column density distribution functions (cddfs) and cosmic densities of si iv, c iv, n v, o vi and ne viii absorbers with observations at redshift z = 0 to ∼6 and find reasonable agreement, although there are some differences. we show that the typical physical densities of the absorbing gas increase with column density and redshift, but decrease with the ionization energy of the absorbing ion. the typical metallicity increases with both column density and time. the fraction of collisionally ionized metal absorbers increases with time and ionization energy. while our results show little sensitivity to the presence or absence of agn feedback, increasing/decreasing the efficiency of stellar feedback by a factor of 2 substantially decreases/increases the cddfs and the cosmic densities of the metal ions. we show that the impact of the efficiency of stellar feedback on the cddfs and cosmic densities is largely due to its effect on the metal production rate. however, the temperatures of the metal absorbers, particularly those of strong o vi, are directly sensitive to the strength of the feedback. | cosmic distribution of highly ionized metals and their physical conditions in the eagle simulations |
we construct a new analytic phenomenological model for the extended circumgalactic material (cgm) of l* galaxies. our model reproduces the o vii/o viii absorption observations of the milky way (mw) and the o vi measurements reported by the cos-halos and ecgm surveys. the warm/hot gas is in hydrostatic equilibrium in an mw gravitational potential, and we adopt a barotropic equation of state, resulting in a temperature variation as a function of radius. a pressure component with an adiabatic index of $\gamma =4/3$ is included to approximate the effects of a magnetic field and cosmic rays. we introduce a metallicity gradient motivated by the enrichment of the inner cgm by the galaxy. we then present our fiducial model for the corona, tuned to reproduce the observed o vi-o viii column densities and with a total mass of ${m}_{\mathrm{cgm}}\approx 5.5\times {10}^{10}$ ${m}_{\odot }$ inside ${r}_{\mathrm{cgm}}\approx 280\,\mathrm{kpc}$ . the gas densities in the cgm are low ( ${n}_{{\rm{h}}}={10}^{-5}\mbox{--}3\times {10}^{-4}$ cm-3), and its collisional ionization state is modified by the metagalactic radiation field. we show that for o vi-bearing warm/hot gas with typical observed column densities ${n}_{{\rm{o}}{\rm{vi}}}\sim 3\times {10}^{14}$ cm-2 at large ( $\gtrsim 100$ kpc) impact parameters from the central galaxies, the ratio of the cooling to dynamical times, ${t}_{\mathrm{cool}}$ / ${t}_{\mathrm{dyn}}$ , has a model-independent upper limit of $\lesssim 4$ . in our model, ${t}_{\mathrm{cool}}$ / ${t}_{\mathrm{dyn}}$ at large radii is $\sim 2\mbox{--}3$ . we present predictions for a wide range of future observations of the warm/hot cgm, from uv/x-ray absorption and emission spectroscopy to dispersion measure and sunyaev-zel'dovich cosmic microwave background measurements. we provide the model outputs in machine-readable data files for easy comparison and analysis. | massive warm/hot galaxy coronae. ii. isentropic model |
quasar proximity zones at $z\gt 5.5$ correspond to overdense and overionized environments. galaxies found inside proximity zones can therefore display features that would otherwise be masked by absorption in the intergalactic medium. we demonstrate the utility of this quasar-galaxy synergy by reporting the discovery of the first three "proximate lyα emitters" (laes) within the proximity zone of quasar j0836+0054 at z = 5.795 (aerith a, b, and c). aerith a, located behind the quasar with an impact parameter ${d}_{\perp }=278\pm 8$ pkpc, provides the first detection of an lyα transverse proximity effect. we model the transmission and show that it constrains the onset of j0836's quasar phase to $0.2\mathrm{myr}\lt t\lt 28\mathrm{myr}$ in the past. the second object, aerith b at a distance $d\lt 912$ pkpc from the quasar, displays a bright and broad double-peaked lyα emission line. the peak separation implies a low ionizing ${f}_{\mathrm{esc}}\lesssim 1 \% $ . we fit the lyα line with an outflowing shell model, finding a typical central density $\mathrm{log}\ {n}_{{\rm{h}}{\rm{i}}}/{\mathrm{cm}}^{-2}={19.3}_{-0.2}^{+0.8}$ , outflow velocity ${v}_{\mathrm{out}}={16}_{-11}^{+4}$ km s-1, and gas temperature $\mathrm{log}t/k={3.8}_{-0.7}^{+0.8}$ compared to $2\lt z\lt 3$ analog laes. we detect object aerith c via an lyα emission line at z = 5.726. this corresponds with the edge of the quasar's proximity zone ( ${\rm{\delta }}z\lt 0.02$ ), suggesting that the proximity zone is truncated by a density fluctuation. via the analyses conducted here, we illustrate how proximate laes offer unique insight into the ionizing properties of both quasars and galaxies during hydrogen reionization. | three lyα emitting galaxies within a quasar proximity zone at z ∼ 5.8 |
we use a background quasar to detect the presence of circumgalactic gas around a z=0.91 low-mass star-forming galaxy. data from the new multi unit spectroscopic explorer (muse) on the very large telescope show that the galaxy has a dust-corrected star formation rate (sfr) of 4.7 ± 2.0 m⊙ yr-1, with no companion down to 0.22 m⊙ yr-1 (5σ) within 240 {h}-1 kpc (“30”). using a high-resolution spectrum of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle α of only 15°), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a “cold-flow disk” extending at least 12 kpc (3× {r}1/2). we estimate the mass accretion rate {\dot{m}}{{in}} to be at least two to three times larger than the sfr, using the geometric constraints from the ifu data and the h i column density of log {n}{{h}{{i}}}/{{cm}}-2 ≃ 20.4 obtained from a hubble space telescope/cos near-uv spectrum. from a detailed analysis of the low-ionization lines (e.g., zn ii, cr ii, ti ii, mn ii, si ii), the accreting material appears to be enriched to about 0.4 {z}⊙(albeit with large uncertainties: {log} z/{z}⊙ =-0.4\quad +/- \quad 0.4), which is comparable to the galaxy metallicity (12 + log o/h = 8.7 ± 0.2), implying a large recycling fraction from past outflows. blueshifted mg ii and fe ii absorptions in the galaxy spectrum from the muse data reveal the presence of an outflow. the mg ii and fe ii absorption line ratios indicate emission infilling due to scattering processes, but the muse data do not show any signs of fluorescent fe ii* emission. based on observations made at the eso telescopes under program 080.a-0364 (sinfoni), 079.a-0600 (uves), and as part of muse commissioning (eso program 060.a-9100). 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 program id 12522. | possible signatures of a cold-flow disk from muse using a z ∼ 1 galaxy-quasar pair toward sdss j1422-0001 |
previous studies have shown that wide-field infrared survey explorer-selected hyperluminous, hot dust-obscured galaxies (hot dogs) are powered by highly dust-obscured, possibly compton-thick active galactic nuclei (agns). high obscuration provides us a good chance to study the host morphology of the most luminous agns directly. we analyze the host morphology of 18 hot dogs at z ∼ 3 using hubble space telescope/wfc3 imaging. we find that hot dogs have a high merger fraction (62 ± 14%). by fitting the surface brightness profiles, we find that the distribution of sérsic indices in our hot dog sample peaks around 2, which suggests that most hot dogs have transforming morphologies. we also derive the agn bolometric luminosity (∼1014 l ⊙) of our hot dog sample by using ir spectral energy distributions decomposition. the derived merger fraction and agn bolometric luminosity relation is well consistent with the variability-based model prediction. both the high merger fraction in an ir-luminous agn sample and relatively low merger fraction in a uv/optical-selected, unobscured agn sample can be expected in the merger-driven evolutionary model. finally, we conclude that hot dogs are merger-driven and may represent a transit phase during the evolution of massive galaxies, transforming from the dusty starburst-dominated phase to the unobscured qso phase. | the most luminous heavily obscured quasars have a high merger fraction: morphological study of wise-selected hot dust-obscured galaxies |
an observational tension on estimates of the hubble parameter, h0, using early and late universe information, is being of intense discussion in the literature. additionally, it is of great importance to measure h0 independently of cmb data and local distance ladder method. in this sense, we analyze 15 measurements of the transversal bao scale, θbao, obtained in a weakly model-dependent approach, in combination with other data sets obtained in a model-independent way, namely, big bang nucleosynthesis (bbn) information, 6 gravitationally lensed quasars with measured time delays by the h0licow team, and measures of cosmic chronometers (cc). we find h0=74 .88-2.1+1.9 km s-1 mpc-1 and h0=72 .06-1.3+1.2 km s-1 mpc-1 from θbao+bbn+h0licow and θbao+bbn+cc, respectively, in fully accordance with local measurements. moreover, we estimate the sound horizon at drag epoch, rd, independent of cmb data, and find rd=144 .1-5.5+5.3 mpc (from θbao+bbn+h0licow) and rd=150 .4-3.3+2.7 mpc (from θbao+bbn+cc). in a second round of analysis, we test how the presence of a possible spatial curvature, ωk, can influence the main results. we compare our constraints on h0 and rd with other reported values. our results show that it is possible to use a robust compilation of transversal bao data, θbao, jointly with other model-independent measurements, in such a way that the tension on the hubble parameter can be alleviated. | bao signatures in the 2-point angular correlations and the hubble tension |
we describe the execution and data reduction of the european southern observatory large programme "quasars and their absorption lines: a legacy survey of the high-redshift universe with vlt/x-shooter" (hereafter "xq-100"). xq-100 has produced and made publicly available a homogeneous and high-quality sample of echelle spectra of 100 quasars (qsos) at redshifts z ≃ 3.5-4.5 observed with full spectral coverage from 315 to 2500 nm at a resolving power ranging from r ~ 4000 to 7000, depending on wavelength. the median signal-to-noise ratios are 33, 25 and 43, as measured at rest-frame wavelengths 1700, 3000 and 3600 å, respectively. this paper provides future users of xq-100 data with the basic statistics of the survey, along with details of target selection, data acquisition and data reduction. the paper accompanies the public release of all data products, including 100 reduced spectra. xq-100 is the largest spectroscopic survey to date of high-redshift qsos with simultaneous rest-frame uv/optical coverage, and as such enables a wide range of extragalactic research, from cosmology and galaxy evolution to agn astrophysics. based on observations made with eso telescopes at the la silla paranal observatory under programme id 189.a-0424.the xq-100 raw data and the xq-100 science data products can be found at http://archive.eso.org/eso/eso_archive_main.html and http://archive.eso.org/wdb/wdb/adp/phase3_main/form, respectively. | xq-100: a legacy survey of one hundred 3.5 ≲ z ≲ 4.5 quasars observed with vlt/x-shooter |
we investigate the dependence of black hole accretion rate (bhar) on host-galaxy star formation rate (sfr) and stellar mass (m *) in the candels/goods-south field in the redshift range of 0.5≤slant z< 2.0. our sample consists of ≈ {{18,000}} galaxies, allowing us to probe galaxies with 0.1{m}⊙ {{yr}}-1≲ {sfr}≲ 100 {m}⊙{{yr}}-1 and/or {10}8{m}⊙ ≲ {m}* ≲ {10}11 {m}⊙ . we use sample-mean bhar to approximate long-term average bhar. our sample-mean bhars are derived from the chandra deep field-south 7 ms observations, while the sfrs and m * have been estimated by the candels team through spectral energy distribution fitting. the average bhar is correlated positively with both sfr and m *, and the bhar-sfr and bhar-m * relations can both be described acceptably by linear models with a slope of unity. however, bhar appears to be correlated more strongly with m * than sfr. this result indicates that m * is the primary host-galaxy property related to supermassive black hole (smbh) growth, and the apparent bhar-sfr relation is largely a secondary effect due to the star-forming main sequence. among our sources, massive galaxies ({m}* ≳ {10}10{m}⊙ ) have significantly higher bhar/sfr ratios than less massive galaxies, indicating that the former have higher smbh fueling efficiency and/or higher smbh occupation fraction than the latter. our results can naturally explain the observed proportionality between {m}{bh} and m * for local giant ellipticals and suggest that their {m}{bh}/{m}*is higher than that of local star-forming galaxies. among local star-forming galaxies, massive systems might have higher {m}{bh}/{m}*compared to dwarfs. | black hole growth is mainly linked to host-galaxy stellar mass rather than star formation rate |
using ≈190 000 spectra from the 17th data release of the sloan digital sky survey (sdss), we investigate the ultraviolet emission line properties in z ≈ 2 quasars. specifically, we quantify how the shape of c iv λ1549 and the equivalent width (ew) of he ii λ1640 depend on the black hole mass and eddington ratio inferred from mg ii λ2800. above l/ledd ≳ 0.2, there is a strong mass dependence in both c iv blueshift and he ii ew. large c iv blueshifts are observed only in regions with both high mass and high accretion rate. including x-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of agn accretion and outflow mechanisms. the observed trends in he ii and 2 kev strength are broadly consistent with theoretical qsosed models of agn spectral energy distributions (seds) for low spin black holes, where the ionizing sed depends on the accretion disc temperature and the strength of the soft excess. high spin models are not consistent with observations, suggesting sdss quasars at z ≈ 2 may in general have low spins. we find a dramatic switch in behaviour at l/ledd ≲ 0.1: the ultraviolet emission properties show much weaker trends, and no longer agree with qsosed predictions, hinting at changes in the structure of the broad line region. overall, the observed emission line trends are generally consistent with predictions for radiation line driving where quasar outflows are governed by the sed, which itself results from the accretion flow and hence depends on both the smbh mass and accretion rate. | testing agn outflow and accretion models with c iv and he ii emission line demographics in z ≈ 2 quasars |
in order to investigate the impact of radio jets on the interstellar medium (ism) of galaxies hosting active galactic nuclei (agn), we present subarcsecond-resolution atacama large millimeter/submillimeter array (alma) co(2-1) and co(3-2) observations of the teacup galaxy. this is a nearby (dl = 388 mpc) radio-quiet type-2 quasar (qso2) with a compact radio jet (pjet ≈ 1043 erg s−1) that subtends a small angle from the molecular gas disc. enhanced emission line widths perpendicular to the jet orientation have been reported for several nearby agn for the ionised gas. for the molecular gas in the teacup, not only do we find this enhancement in the velocity dispersion but also a higher brightness temperature ratio (t32/t21) perpendicular to the radio jet compared to the ratios found in the galaxy disc. our results and the comparison with simulations suggest that the radio jet is compressing and accelerating the molecular gas, and driving a lateral outflow that shows enhanced velocity dispersion and higher gas excitation. these results provide further evidence that the coupling between the jet and the ism is relevant to agn feedback even in the case of radio-quiet galaxies. | jet-induced molecular gas excitation and turbulence in the teacup |
we provide predictions of the yield of 7 < z < 9 quasars from the euclid wide survey, updating the calculation presented in the euclid red book in several ways. we account for revisions to the euclid near-infrared filter wavelengths; we adopt steeper rates of decline of the quasar luminosity function (qlf; φ) with redshift, φ ∝ 10k(z - 6), k = -0.72, and a further steeper rate of decline, k = -0.92; we use better models of the contaminating populations (mlt dwarfs and compact early-type galaxies); and we make use of an improved bayesian selection method, compared to the colour cuts used for the red book calculation, allowing the identification of fainter quasars, down to jab ∼ 23. quasars at z > 8 may be selected from euclid oyjh photometry alone, but selection over the redshift interval 7 < z < 8 is greatly improved by the addition of z-band data from, e.g., pan-starrs and lsst. we calculate predicted quasar yields for the assumed values of the rate of decline of the qlf beyond z = 6. if the decline of the qlf accelerates beyond z = 6, with k = -0.92, euclid should nevertheless find over 100 quasars with 7.0 < z < 7.5, and ∼25 quasars beyond the current record of z = 7.5, including ∼8 beyond z = 8.0. the first euclid quasars at z > 7.5 should be found in the dr1 data release, expected in 2024. it will be possible to determine the bright-end slope of the qlf, 7 < z < 8, m1450 < -25, using 8 m class telescopes to confirm candidates, but follow-up with jwst or e-elt will be required to measure the faint-end slope. contamination of the candidate lists is predicted to be modest even at jab ∼ 23. the precision with which k can be determined over 7 < z < 8 depends on the value of k, but assuming k = -0.72 it can be measured to a 1σ uncertainty of 0.07. | euclid preparation. v. predicted yield of redshift 7 < z < 9 quasars from the wide survey |
hydrodynamical simulations are increasingly able to accurately model physical systems on stellar, galactic, and cosmological scales; however, the utility of these simulations is often limited by our ability to directly compare them with the data sets produced by observers: spectra, photometry, etc. to address this problem, we have created trident, a python-based open-source tool for post-processing hydrodynamical simulations to produce synthetic absorption spectra and related data. trident can (i) create absorption-line spectra for any trajectory through a simulated data set mimicking both background quasar and down-the-barrel configurations; (ii) reproduce the spectral characteristics of common instruments like the cosmic origins spectrograph; (iii) operate across the ultraviolet, optical, and infrared using customizable absorption-line lists; (iv) trace simulated physical structures directly to spectral features; (v) approximate the presence of ion species absent from the simulation outputs; (vi) generate column density maps for any ion; and (vii) provide support for all major astrophysical hydrodynamical codes. trident was originally developed to aid in the interpretation of observations of the circumgalactic medium and intergalactic medium, but it remains a general tool applicable in other contexts. | trident: a universal tool for generating synthetic absorption spectra from astrophysical simulations |
we compare the constraints from two (2019 and 2021) compilations of h ii starburst galaxy (h iig) data and test the model independence of quasar (qso) angular size data using six spatially flat and non-flat cosmological models. we find that the new 2021 compilation of h iig data generally provides tighter constraints and prefers lower values of cosmological parameters than those from the 2019 h iig data. qso data by themselves give relatively model-independent constraints on the characteristic linear size, lm, of the qsos within the sample. we also use hubble parameter [h(z)], baryon acoustic oscillation (bao), pantheon type ia supernova (sn ia) apparent magnitude (sn-pantheon), and des-3 yr binned sn ia apparent magnitude (sn-des) measurements to perform joint analyses with h iig and qso angular size data, since their constraints are not mutually inconsistent within the six cosmological models we study. a joint analysis of h(z), bao, sn-pantheon, sn-des, qso, and the newest compilation of h iig data provides almost model-independent summary estimates of the hubble constant, $h_0=69.7\pm 1.2\ \rm {km\,s^{-1}\,mpc^{-1}}$, the non-relativistic matter density parameter, $\omega _{\rm m_0}=0.293\pm 0.021$, and lm = 10.93 ± 0.25 pc. | cosmological constraints from h ii starburst galaxy, quasar angular size, and other measurements |
both theory and observations suggest that outflows driven by an active central supermassive black hole have a feedback effect on shaping the global properties of the host galaxy1-8. however, whether feedback from the outflow is effective, and if so, whether it is positive or negative, have long been controversial. here, using the latest catalogue from the sloan digital sky survey, we use the flux ratio of the [o ii] to [ne v] emission lines as a proxy to compare the star formation rate in the hosts of quasars with different types of broad absorption lines (bals): low-ionization (lo)bal, high-ionization (hi)bal and non-bal. we find that the star formation rate decreases from lobal to hibal quasars, and then increases from hibal to non-bal quasars. assuming that the sequence of lobal to hibal to non-bal represents evolution, our results are consistent with a quenching and subsequent rebound of star formation in quasar host galaxies. this phenomenon can be explained by suppression of the star formation rate by the outflow and then rebound of the rate once the outflow disappears as the quasars evolve from hibals to non-bals. our result suggests that the quasar outflow has a negative global feedback on galaxy evolution. | evidence for the connection between star formation rate and the evolutionary phases of quasars |
the quest for high-redshift quasars has led to a series of record-breaking sources, with the current record holder at z = 7.642. here, we show how future detections of z > 8 quasars impact the constraints on the parameters for black hole growth and seed models. using broad flat priors on the growth parameters (eddington ratio $\, {f_{\rm edd}}$, duty cycle ${\cal d}$, seed mass m•,seed, and radiative efficiency ϵ), we show that the large uncertainties in their determination decrease by a factor ~5 when a quasar's detection redshift goes from z = 9 to z = 12. in this high-redshift regime, ϵ tends to the lowest value allowed, and the distribution for m•,seed peaks well inside the heavy seed domain. remarkably, two quasars detected at z > 7 with low accretion rates (j1243+0100 and j0313-1806) already tighten the available parameter space, requiring $m_{\rm \bullet , seed} \gt 10^{3.5} \, {\rm m_\odot }$ and ϵ < 0.1. the radiative efficiency is a crucial unknown, with factor ~2 changes able to modify the predicted mass by ~3 orders of magnitude already at z ~ 9. the competing roles of inefficient accretion (decreasing ϵ) and black hole spin-up (increasing ϵ) significantly impact growth models. finally, we suggest that yields currently predicted by upcoming quasar surveys (e.g. euclid) will be instrumental for determining the most-likely seed mass regime. for example, assuming thin-disc accretion, a detection of a quasar with $m_\bullet \sim 10^{10} \, {\rm m_\odot }$ by z ~ 9-10 would exclude the entire parameter space available for light seeds and dramatically reduce the one for heavy seeds. | the search for the farthest quasar: consequences for black hole growth and seed models |
we report the first results of a high-redshift (z ≳ 5) quasar survey using the dark energy spectroscopic instrument (desi). as a desi secondary target program, this survey is designed to carry out a systematic search and investigation of quasars at 4.8 < z < 6.8. the target selection is based on the desi legacy imaging surveys (the legacy surveys) dr9 photometry, combined with the pan-starrs1 data and j-band photometry from public surveys. a first quasar sample has been constructed from the desi survey validation 3 (sv3) and first-year observations until 2022 may. this sample includes more than 400 new quasars at redshift 4.7 ≤ z < 6.6, down to 21.5 magnitude (ab) in the z band, discovered from 35% of the entire target sample. remarkably, there are 220 new quasars identified at z ≥ 5, more than one-third of existing quasars previously published at this redshift. the observations so far result in an average success rate of 23% at z > 4.7. the current spectral data set has already allowed analysis of interesting individual objects (e.g., quasars with damped lyα absorbers and broad absorption line features), and statistical analysis will follow the survey's completion. a set of science projects will be carried out leveraging this program, including quasar luminosity function, quasar clustering, intergalactic medium, quasar spectral properties, intervening absorbers, and properties of early supermassive black holes. additionally, a sample of 38 new quasars at z ~ 3.8-5.7 discovered from a pilot survey in the desi sv1 is also published in this paper. | desi z ≳ 5 quasar survey. i. a first sample of 400 new quasars at z 4.7-6.6 |
supermassive black holes weighing up to ∼109 m ⊙ are in place by z ∼ 7, when the age of the universe is ≲1 gyr. this implies a time crunch for their growth, since such high masses cannot be easily reached in standard accretion scenarios. here, we explore the physical conditions that would lead to optimal growth wherein stable super-eddington accretion would be permitted. our analysis suggests that the preponderance of optimal conditions depends on two key parameters: the black hole mass and the host galaxy central gas density. in the high-efficiency region of this parameter space, a continuous stream of gas can accrete onto the black hole from large to small spatial scales, assuming a global isothermal profile for the host galaxy. using analytical initial mass functions for black hole seeds, we find an enhanced probability of high-efficiency growth for seeds with initial masses ≳104 m ⊙. our picture suggests that a large population of high-z lower-mass black holes that formed in the low-efficiency region, with low duty cycles and accretion rates, might remain undetectable as quasars, since we predict their bolometric luminosities to be ≲1041 erg s-1. the presence of these sources might be revealed only via gravitational wave detections of their mergers. | conditions for optimal growth of black hole seeds |
past x-ray observations of the nearby luminous quasar pds 456 (at z = 0.184) have revealed a wide-angle accretion disk wind with an outflow velocity of ∼-0.25c, as observed through observations of its blueshifted iron k-shell absorption line profile. here we present three new xmm-newton observations of pds 456: one in 2018 september where the quasar was bright and featureless and two in 2019 september, 22 days apart, occurring when the quasar was five times fainter and where strong blueshifted lines from the wind were present. during the second 2019 september observation, three broad (σ = 3000 km s-1) absorption lines were resolved in the high-resolution reflection grating spectrometer spectrum that are identified with blueshifted o viii lyα, ne ix heα, and ne x lyα. the outflow velocity of this soft x-ray absorber was found to be v/c = -0.258 ± 0.003, fully consistent with an iron k absorber with v/c = -0.261 ± 0.007. the ionization parameter and column density of the soft x-ray component (log ξ = 3.4, nh = 2 × 1021 cm-2) outflow was lower by about 2 orders of magnitude when compared to the high-ionization wind at iron k (log ξ = 5, nh = 7 × 1023 cm-2). substantial variability was seen in the soft x-ray absorber between the 2019 observations, declining from nh = 1023 to 1021 cm-2 over 20 days, while the iron k component was remarkably stable. we conclude that the soft x-ray wind may originate from an inhomogeneous wind streamline passing across the line of sight that, due to its lower ionization, is located further from the black hole, on parsec scales, than the innermost disk wind. | resolving the soft x-ray ultrafast outflow in pds 456 |
this is the third in a series of papers reporting on a large reverberation-mapping campaign aimed to study the properties of active galactic nuclei (agns) with high accretion rates. we present new results on the variability of the optical fe ii emission lines in 10 agns observed by the yunnan observatory 2.4 m telescope from 2012 to 2013. we detect statistically significant time lags, relative to the agn continuum, in nine of the sources. this accurate measurement is achieved using a sophisticated spectral fitting scheme that allows for apparent flux variations of the host galaxy, and several narrow lines, due to the changing observing conditions. six of the newly detected lags are indistinguishable from the hβ lags measured in the same sources. two are significantly longer and one is slightly shorter. combining these findings with the fe ii lags reported in previous studies, we find an fe ii radius-luminosity relationship similar to the one for hβ, although our sample by itself shows no clear correlation. the results support the idea that fe ii emission lines originate in photoionized gas, which, for the majority of the newly reported objects, is indistinguishable from the hβ-emitting gas. we also present a tentative correlation between the lag and intensity of fe ii and hβ and comment on its possible origin. | supermassive black holes with high accretion rates in active galactic nuclei. iii. detection of fe ii reverberation in nine narrow-line seyfert 1 galaxies |
we present two catalogs of radio-loud candidate blazars whose wide-field infrared survey explorer (wise) mid-infrared colors are selected to be consistent with the colors of confirmed γ-ray-emitting blazars. the first catalog is the improved and expanded release of the wise blazar-like radio-loud sources (wibrals) catalog presented by d’abrusco et al. it includes sources detected in all four wise filters, spatially cross-matched with radio sources in one of three radio surveys and radio-loud based on their q 22 spectral parameter. wibrals2 includes 9541 sources classified as bl lacs, flat-spectrum radio quasars, or mixed candidates based on their wise colors. the second catalog, called kdebllacs, based on a new selection technique, contains 5579 candidate bl lacs extracted from the population of wise sources detected in the first three wise passbands ([3.4], [4.6], and [12]) only, whose mid-infrared colors are similar to those of confirmed, γ-ray bl lacs. members of kdbllacs are also required to have a radio counterpart and be radio-loud based on the parameter q 12, defined similarly to the q 22 used for the wibrals2. we describe the properties of these catalogs and compare them with the largest samples of confirmed and candidate blazars in the literature. we cross-match the two new catalogs with the most recent catalogs of γ-ray sources detected by the fermi large area telescope. since spectroscopic observations of candidate blazars from the first wibrals catalog within the uncertainty regions of γ-ray unassociated sources confirmed that ∼90% of these candidates are blazars, we anticipate that these new catalogs will again play an important role in the identification of the γ-ray sky. | two new catalogs of blazar candidates in the wise infrared sky |
we announce the second data release (dr2) of the noirlab source catalog (nsc), using 412,116 public images from ctio-4 m+decam, the kpno-4 m+mosaic3, and the bok-2.3 m+90prime. nsc dr2 contains over 3.9 billion unique objects, 68 billion individual source measurements, covers ≈35,000 square degrees of the sky, has depths of ≈23 mag in most broadband filters with ≈1%-2% photometric precision, and astrometric accuracy of ≈7 mas. approximately 1.9 billion objects within ≈30,000 square degrees of sky have photometry in three or more bands. there are several improvements over nsc dr1. dr2 includes 156,662 (61%) more exposures extending over 2 more years than in dr1. the southern photometric zero-points in griz are more accurate by using the skymapper dr1 and atlas-ref2 catalogs, and improved extinction corrections were used for high-extinction regions. in addition, the astrometric accuracy is improved by taking advantage of gaia dr2 proper motions when calibrating the astrometry of individual images. this improves the nsc proper motions to ∼2.5 mas yr-1 (precision) and ∼0.2 mas yr-1 (accuracy). the combination of sources into unique objects is performed using a dbscan algorithm and mean parameters per object (such as mean magnitudes, proper motion, etc.) are calculated more robustly with outlier rejection. finally, eight multi-band photometric variability indices are calculated for each object and variable objects are flagged (23 million objects). nsc dr2 will be useful for exploring solar system objects, stellar streams, dwarf satellite galaxies, quasi-stellar objects, variable stars, high proper-motion stars, and transients. several examples of these science use cases are presented. the nsc dr2 catalog is publicly available via the noirlab's astro data lab science platform. | second data release of the all-sky noirlab source catalog |
compact objects are expected to exist in the accretion disks of supermassive black holes (smbhs) in active galactic nuclei (agns), and in the presence of such a dense environment (∼1014 cm-3), they will form a new kind of stellar population denoted as accretion-modified stars (amss). this hypothesis is supported by recent ligo/virgo detection of the mergers of very high-mass stellar binary black holes (bhs). we show that the amss will be trapped by the smbh disk within a typical agn lifetime. in the context of smbh disks, the rates of bondi accretion onto bhs are ∼109ledd/c2, where ledd is the eddington luminosity and c is the speed of light. outflows developed from the hyper-eddington accretion strongly impact the bondi sphere and induce episodic accretion. we show that the hyper-eddington accretion will be halted after an accretion interval of ta ∼ 105m1 s, where m1 = m•/10m⊙ is the bh mass. the kinetic energy of the outflows accumulated during ta is equivalent to 10 supernovae driving an explosion of the bondi sphere and developing blast waves. we demonstrate that a synchrotron flare from relativistic electrons accelerated by the blast waves peaks in the soft x-ray band (∼0.1 kev), significantly contributing to the radio, optical, uv, and soft x-ray emission of typical radio-quiet quasars. external inverse compton scattering of the electrons peaks around 40 gev and is detectable through fermi-lat. the flare, decaying with t-6/5 with a few months, will appear as a slowly varying transient. the flares, occurring at a rate of a few per year in radio-quiet quasars, provide a new mechanism for explaining agn variability. | accretion-modified stars in accretion disks of active galactic nuclei: slowly transient appearance |
we study the early growth of massive seed black holes (bhs) via accretion in protogalactic nuclei where the stellar bulge component is assembled, performing axisymmetric two-dimensional radiation hydrodynamical simulations. we find that when a seed bh with m • ~ 105 m ⊙ is embedded in dense metal-poor gas (z = 0.01 z ⊙) with a density of ≳ 100 cm-3 and bulge stars with a total mass of m ⋆ ≳ 100 m •, a massive gaseous disk feeds the bh efficiently at rates of ≳ 0.3-1 m ⊙ yr-1, and the bh mass increases nearly tenfold within ~2 myr. this rapid accretion phase lasts until a good fraction of the gas bounded within the bulge accretes onto the bh, although the feeding rate is regulated owing to strong outflows driven by ionizing radiation emitted from the accreting bh. the transient growing mode can be triggered for seed bhs formed in massive dark-matter halos with masses of ≳ 109 m ⊙ at z ~ 15-20 (the virial temperature is t vir ≃ 105 k). the host halos are heavier and rarer than those of typical first galaxies, but are more likely to end up in quasar hosts by z ≃ 6. this mechanism naturally yields a mass ratio of m •/m ⋆ > 0.01 higher than the value seen in the local universe. the existence of such overmassive bhs provides us with a unique opportunity to detect highly accreting seed bhs at z ~ 15 with ab magnitude of m ab ~ 26-29 mag at 2 μm (rest frame 10 ev) by the upcoming observations by the james webb space telescope and nancy grace roman space telescope. | rapid growth of seed black holes during early bulge formation |
the elemental abundances in the broad-line regions of high-redshift quasars trace the chemical evolution in the nuclear regions of massive galaxies in the early universe. in this work, we study metallicity-sensitive broad emission-line flux ratios in rest-frame uv spectra of 25 high-redshift (5.8 < z < 7.5) quasars observed with the vlt/x-shooter and gemini/gnirs instruments, ranging over $\log \left({{m}_{\rm {bh}}/\rm {m}_{\odot }}\right) = 8.4-9.8$ in black hole mass and $\log \left(\rm {l}_{\rm {bol}}/\rm {erg \, s}^{-1}\right) = 46.7-47.7$ in bolometric luminosity. we fit individual spectra and composites generated by binning across quasar properties: bolometric luminosity, black hole mass, and blueshift of the c iv line, finding no redshift evolution in the emission-line ratios by comparing our high-redshift quasars to lower redshift (2.0 < z < 5.0) results presented in the literature. using cloudy-based locally optimally emitting cloud photoionization model relations between metallicity and emission-line flux ratios, we find the observable properties of the broad emission lines to be consistent with emission from gas clouds with metallicity that are at least 2-4 times solar. our high-redshift measurements also confirm that the blueshift of the c iv emission line is correlated with its equivalent width, which influences line ratios normalized against c iv. when accounting for the c iv blueshift, we find that the rest-frame uv emission-line flux ratios do not correlate appreciably with the black hole mass or bolometric luminosity. | chemical abundance of z ∼ 6 quasar broad-line regions in the xqr-30 sample |
we predict the observational signatures of galaxy scale outflows powered by active galactic nuclei (agn). most of the emission is produced by the forward shock driven into the ambient interstellar medium (ism) rather than by the reverse shock. agn-powered galactic winds with energetics suggested by phenomenological feedback arguments should produce spatially extended ∼1-10 kev x-ray emission ∼ 1041-44 erg s- 1, significantly in excess of the spatially extended x-ray emission associated with normal star-forming galaxies. the presence of such emission is a direct test of whether agn outflows significantly interact with the ism of their host galaxy. we further show that even radio-quiet quasars should have a radio luminosity comparable to or in excess of the far-infrared-radio correlation of normal star-forming galaxies. this radio emission directly constrains the total kinetic energy flux in agn-powered galactic winds. radio emission from agn wind shocks can also explain the recently highlighted correlations between radio luminosity and the kinematics of agn narrow-line regions in radio-quiet quasars. | observational signatures of galactic winds powered by active galactic nuclei |
we present damped harmonic oscillator (dho) light-curve modeling for a sample of 12,714 spectroscopically confirmed quasars in the sloan digital sky survey stripe 82 region. dho is a second-order continuous-time autoregressive moving-average process, which can be fully described using four independent parameters: a natural oscillation frequency (ω 0), a damping ratio (ξ), a characteristic perturbation timescale (τ perturb), and an amplitude for the perturbing white noise (σϵ ). the asymptotic variability amplitude of a dho process is quantified by σ dho-a function of ω 0, ξ, τ perturb, and σϵ . we find that both τ perturb and σϵfollow different dependencies with rest-frame wavelength (λ rf) on either side of 2500 å, whereas σ dho follows a single power-law relation with λ rf. after correcting for wavelength dependence, σ dho exhibits anticorrelations with both the eddington ratio and the black hole mass, while τ perturb-with a typical value of days in the rest frame-shows an anticorrelation with the bolometric luminosity. modeling active galactic nuclei (agn) variability as a dho offers more insight into the workings of accretion disks close to the supermassive black holes at the center of agn. the newly discovered short-term variability (characterized by τ perturb and σϵ ) and its correlation with bolometric luminosity pave the way for new algorithms that will derive fundamental properties (e.g., eddington ratio) of agn using photometric data alone. | examining agn uv/optical variability beyond the simple damped random walk |
motivated by recent measurements of the number density of faint agn at high redshift, we investigate the contribution of quasars to reionization by tracking the growth of central supermassive black holes in an update of the meraxes semi-analytic model. the model is calibrated against the observed stellar mass function at z ∼ 0.6-7, the black hole mass function at z ≲ 0.5, the global ionizing emissivity at z ∼ 2-5 and the thomson scattering optical depth. the model reproduces a magorrian relation in agreement with observations at z < 0.5 and predicts a decreasing black hole mass towards higher redshifts at fixed total stellar mass. with the implementation of an opening angle of 80 deg for quasar radiation, corresponding to an observable fraction of ∼23.4 per cent due to obscuration by dust, the model is able to reproduce the observed quasar luminosity function at z ∼ 0.6-6. the stellar light from galaxies hosting faint active galactic nucleus (agn) contributes a significant or dominant fraction of the uv flux. at high redshift, the model is consistent with the bright end quasar luminosity function and suggests that the recent faint z ∼ 4 agn sample compiled by giallongo et al. (2015) includes a significant fraction of stellar light. direct application of this luminosity function to the calculation of agn ionizing emissivity consequently overestimates the number of ionizing photons produced by quasars by a factor of 3 at z ∼ 6. we conclude that quasars are unlikely to make a significant contribution to reionization. | dark-ages reionization and galaxy formation simulation - x. the small contribution of quasars to reionization |
we present a newly discovered correlation between the wind outflow velocity and the x-ray luminosity in the luminous (lbol ∼ 1047erg s - 1) nearby (z = 0.184) quasar pds 456. all the contemporary xmm-newton, nustar and suzaku observations from 2001-2014 were revisited and we find that the centroid energy of the blueshifted fe k absorption profile increases with luminosity. this translates into a correlation between the wind outflow velocity and the hard x-ray luminosity (between 7 and 30 kev) where we find that v_w/c∝ l_{7-30}^{γ } where γ = 0.22 ± 0.04. we also show that this is consistent with a wind that is predominately radiatively driven, possibly resulting from the high eddington ratio of pds 456. | evidence for a radiatively driven disc-wind in pds 456? |
in the context of a cosmography approach to using the data of the hubble diagram for supernovae, quasars, and gamma-ray bursts, we study dark energy (de) parameterizations and the concordance cold dark matter (λcdm) universe. using different combinations of data samples including (i) supernovae (pantheon), (ii) pantheon + quasars. and (iii) pantheon + quasars + gamma-ray bursts, and applying the minimization of χ2 function of the distance modulus of data samples in the context of the markov chain monte carlo method, we obtain constrained values of cosmographic parameters in a model-independent cosmography scenario. we then investigate our analysis, for different concordance λcdm cosmology, wcdm, chevallier-polarski-linder, and pade parameterizations. comparing the numerical values of the cosmographic parameters obtained for de scenarios with those of the model-independent method, we show that the concordance λcdm model has serious issues when we involve quasar and gamma-ray burst data in our analysis. while high-redshift quasars and gamma-ray bursts can falsify the concordance model, our results using a cosmography approach indicate that the other de parameterizations are still consistent with these observations. | a cosmography approach to dark energy cosmologies: new constraints using the hubble diagrams of supernovae, quasars, and gamma-ray bursts |
we report new observations from a systematic, spectroscopic, ultraviolet absorption-line survey that maps the spatial and kinematic properties of the high velocity gas in the galactic center (gc) region. we examine the hypothesis that this gas traces the biconical nuclear outflow. we use an ultraviolet spectra of 47 background qsos and halo stars projected inside and outside the northern fermi bubble from the hubble space telescope to study the incidence of high velocity absorption around it. we use five lines of sight inside the northern fermi bubble to constrain the velocity and column densities of outflowing gas traced by o i, al ii, c ii, c iv, si ii, si iii, si iv, and other species. we find that all five lines of sight inside the northern fermi bubble exhibit blueshifted high velocity absorption components, whereas only 9 out of the 42 lines of sight outside the northern fermi bubble exhibit blueshifted high velocity absorption components. the observed outflow velocity profile decreases with galactic latitude and radial distance (r) from the gc. the observed blueshifted velocities change from {v}{gsr}=-265 {km} {{{s}}}-1 at r ≈ 2.3 kpc to {v}{gsr}=-91 {km} {{{s}}}-1 at r ≈ 6.5 kpc. we derive the metallicity of the entrained gas along the 1h1613-097 sightline, one that passes through the center of the northern fermi bubble, finding [o/h] ≳ -0.54 ± 0.15. a simple kinematic model, tuned to match the observed absorption component velocities along the five lines of sight inside the bubble, constrains the outflow velocities to ≈1000-1300 {km} {{{s}}}-1, and the age of the outflow to be ∼6-9 myr. we estimate a minimum mass outflow rate for the nuclear outflow to be ≳ 0.2{m}⊙{{yr}}-1. combining the age and mass outflow rates, we determine a minimum mass of total uv-absorbing cool gas entrained in the fermi bubbles to be ≳ 2× {10}6 {m}⊙ . | mapping the nuclear outflow of the milky way: studying the kinematics and spatial extent of the northern fermi bubble |
context. the ionizing lyman continuum flux escaping from high-redshift galaxies into the intergalactic medium is a fundamental quantity to understand the physical processes involved in the reionization epoch. however, from an observational point of view, direct detections of hi ionizing photons at high redshifts are feasible for galaxies mainly in the interval z ~ 3-4.aims: we have investigated a sample of star-forming galaxies at z ~ 3.3 to search for possible detections of lyman continuum ionizing photons escaping from galaxy halos.methods: we used deep ultraviolet (uv) imaging in the cosmos field, obtained with the prime focus camera lbc at the lbt telescope, along with a catalogue of spectroscopic redshifts obtained by the vimos ultra deep survey (vuds) to build a sample of 45 galaxies at z ~ 3.3 with l> 0.5 l∗. we obtained deep lbc images of galaxies with spectroscopic redshifts in the interval 3.27 <z< 3.40 both in the r- and deep u-bands (magnitude limit u ~ 29.7 at s/n = 1). at these redshifts, the r-band samples the non-ionizing 1500 å rest-frame luminosity and the u-band samples the rest-frame spectral region just short-ward of the lyman edge at 912 å. their flux ratio is related to the ionizing escape fraction after statistical removal of the absorption by the intergalactic medium along the line of sight.results: a subsample of ten galaxies apparently shows escape fractions >28%, but a detailed analysis of their properties reveals that, with the exception of two marginal detections (s/n ~ 2) in the u-band, all the other eight galaxies are most likely contaminated by the uv flux of low-redshift interlopers located close (in angular position) to the high-z targets. the average escape fraction derived from the stacking of the cleaned sample was constrained to fescrel < 2%. the implied hydrogen photoionization rate is a factor two lower than that needed to keep the intergalactic medium ionized at z ~ 3, as observed in the lyman-α forest of high-z quasar spectra or by the proximity effect.conclusions: these results support a scenario where high redshift, relatively bright (l ≥ 0.5l∗) star-forming galaxies alone are unable to sustain the level of ionization observed in the cosmic intergalactic medium at z ~ 3. star-forming galaxies at higher redshift and at fainter luminosities (l ≪ l∗) can only be major contributors to the reionization of the universe if their physical properties are subject to rapid changes from z ~ 3 to z ~ 6-10. alternatively, ionizing sources could be discovered looking for fainter sources among the active galactic nuclei population at high redshift. based on data obtained with the european southern observatory very large telescope, paranal, chile, under large programme 185.a-0791 and on observations made at the large binocular telescope (lbt) at mt. graham (arizona, usa). | the lyman continuum escape fraction of galaxies at z = 3.3 in the vuds-lbc/cosmos field |
quasars with extremely red infrared-to-optical colours are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called agn unified model. to identify such a population, we match the quasar catalogues of the sloan digital sky survey (sdss), the baryon oscillation spectroscopic survey (boss) to the wide-field infrared survey explorer (wise) to identify quasars with extremely high infrared-to-optical ratios. we identify 65 objects with rab - w4vega > 14 mag (i.e. fν(22 μm)/fν(r) ≳ 1000). this sample spans a redshift range of 0.28 < z < 4.36 and has a bimodal distribution, with peaks at z ∼ 0.8 and z ∼ 2.5. it includes three z > 2.6 objects that are detected in the w4 band but not w1 or w2 (i.e. `w1w2 dropouts'). the sdss/boss spectra show that the majority of the objects are reddened type 1 quasars, type 2 quasars (both at low and high redshift) or objects with deep low-ionization broad absorption lines (bals) that suppress the observed r-band flux. in addition, we identify a class of type 1 permitted broad emission-line objects at z ≃ 2-3 which are characterized by emission line rest-frame equivalent widths (rews) of ≳150 å, much larger than those of typical quasars. in particular, 55 per cent (45 per cent) of the non-bal type 1s with measurable c iv in our sample have rew(c iv) > 100 (150) å, compared to only 5.8 per cent (1.3 per cent) for non-bal quasars in boss. these objects often also have unusual line ratios, such as very high n v/ly α ratios. these large rews might be caused by suppressed continuum emission analogous to type 2 quasars; however, there is no obvious mechanism in standard unified models to suppress the continuum without also obscuring the broad emission lines. | extremely red quasars from sdss, boss and wise: classification of optical spectra |
the idea that photons can convert to axion-like particles (alps) γ → a in or around an agn and reconvert back to photons a → γ in the milky way magnetic field has been put forward in 2008 and has recently attracted growing interest. yet, so far nobody has estimated the conversion probability γ → a as carefully as allowed by present-day knowledge. our aim is to fill this gap. we first remark that agn which can be detected above 100 gev are blazars, namely agn with jets, with one of them pointing towards us. moreover, blazars fall into two well defined classes: bl lac objects (bl lacs) and flat spectrum radio quasars (fsrqs), with drastically different properties. in this letter we report a preliminary evaluation of the γ → a conversion probability inside these two classes of blazars. our findings are surprising. indeed, while in the case of bl lacs the conversion probability turns out to be totally unpredictable due to the strong dependence on the values of the somewhat uncertain position of the emission region along the jet and strength of the magnetic field therein, for fsrqs we are able to make a clear-cut prediction. our results are of paramount importance in view of the planned very-high-energy photon detectors like the cta, hawk, gamma-400 and hiscore. | photons to axion-like particles conversion in active galactic nuclei |
we present rest-frame lyα equivalent widths (ew0) of 417 lyα emitters (laes) detected with multi unit spectroscopic explorer (muse) on the very large telescope (vlt) at 2.9 <z< 6.6 in the hubble ultra deep field. based on the deep muse spectroscopy and ancillary hubble space telescope (hst) photometry data, we carefully measured ew0 values taking into account extended lyα emission and uv continuum slopes (β). our laes reach unprecedented depths, both in lyα luminosities and uv absolute magnitudes, from log (llyα/erg s-1) 41.0 to 43.0 and from muv -16 to -21 (0.01-1.0 l*z=3). the ew0 values span the range of 5 to 240 å or larger, and their distribution can be well fitted by an exponential law n = n0 exp(-ew0/w0). owing to the high dynamic range in muv, we find that the scale factor, w0, depends on muv in the sense that including fainter muv objects increases w0, i.e., the ando effect. the results indicate that selection functions affect the ew0 scale factor. taking these effects into account, we find that our w0 values are consistent with those in the literature within 1σ uncertainties at 2.9 < z < 6.6 at a given threshold of muv and llyα. interestingly, we find 12 objects with ew0> 200 å above 1σ uncertainties. two of these 12 laes show signatures of merger or agn activity: the weak civλ1549 emission line. for the remaining 10 very large ew0 laes, we find that the ew0 values can be reproduced by young stellar ages (< 100 myr) and low metallicities (≲ 0.02 z⊙). otherwise, at least part of the lyα emission in these laes needs to arise from anisotropic radiative transfer effects, fluorescence by hidden agn or quasi-stellar object activity, or gravitational cooling. | the muse hubble ultra deep field survey. x. lyα equivalent widths at 2.9 < z < 6.6 |
reconstruction techniques for intrinsic quasar continua are crucial for the precision study of lyman α (ly α) and lyman β (ly β) transmission at z > 5.5, where the λ < 1215 å emission of quasars is nearly completely absorbed. while the number and quality of spectroscopic observations have become theoretically sufficient to quantify ly α transmission at 5.0 < z < 6.0 to better than $1{{\ \rm per\ cent}}$, the biases and uncertainties arising from predicting the unabsorbed continuum are not known to the same level. in this paper, we systematically evaluate eight reconstruction techniques on a unified testing sample of 2.7 < z < 3.5 quasars drawn from the extended baryon oscillation spectroscopic survey. the methods include power-law extrapolation, stacking of neighbours, and six variants of principal component analysis (pca) using direct projection, fitting of components, or neural networks to perform weight mapping. we find that power-law reconstructions and the pca with fewest components and smallest training sample display the largest biases in the ly α forest (${-}9.58{{\ \rm per\ cent}}/{+}8.22{{\ \rm per\ cent}}$, respectively). power-law extrapolations have larger scatters than previously assumed of ${+}13.1{{\ \rm per\ cent}}/{-}13.2{{\ \rm per\ cent}}$ over ly α and ${+}19.9{{\ \rm per\ cent}}/{-}20.1{{\ \rm per\ cent}}$ over ly β. we present two new pcas that achieve the best current accuracies of $9{{\ \rm per\ cent}}$ for ly α and $17{{\ \rm per\ cent}}$ for ly β. we apply the eight techniques after accounting for wavelength-dependent biases and scatter to a sample of 19 quasars at z > 5.7 with ir x-shooter spectroscopy, obtaining well-characterized measurements for the mean flux transmission at 4.7 < z < 6.3. our results demonstrate the importance of testing and, when relevant, training, continuum reconstruction techniques in a systematic way. | a comparison of quasar emission reconstruction techniques for z ≥ 5.0 lyman α and lyman β transmission |
we use 38 c iv quasar (qso) reverberation-mapped observations, which span eight orders of magnitude in luminosity and the redshift range 0.001064 ≤ z ≤ 3.368, to simultaneously constrain cosmological-model and qso radius-luminosity (r-l) relation parameters in six cosmological models, using an improved technique that more correctly accounts for the asymmetric errors bars of the time-lag measurements. we find that r-l relation parameters are independent of the cosmological models used in the analysis and so the r-l relation can be used to standardize the c iv qsos. the c iv qso cosmological constraints are consistent with those from mg ii qsos, allowing us to derive joint c iv + mg ii qso cosmological constraints which are consistent with currently accelerated cosmological expansion, as well as consistent with cosmological constraints derived using better-established baryon acoustic oscillation (bao) and hubble parameter [h(z)] measurements. when jointly analysed with h(z) + bao data, current c iv + mg ii qso data mildly tighten current h(z) + bao data cosmological constraints. | standardizing reverberation-measured c iv time-lag quasars, and using them with standardized mg ii quasars to constrain cosmological parameters |
microquasars are stellar-mass black holes accreting matter from a companion star and ejecting plasma jets at almost the speed of light. they are analogues of quasars that contain supermassive black holes of 106 to 1010 solar masses. accretion in microquasars varies on much shorter timescales than in quasars and occasionally produces exceptionally bright x-ray flares. how the flares are produced is unclear, as is the mechanism for launching the relativistic jets and their composition. an emission line near 511 kiloelectronvolts has long been sought in the emission spectrum of microquasars as evidence for the expected electron-positron plasma. transient high-energy spectral features have been reported in two objects, but their positron interpretation remains contentious. here we report observations of γ-ray emission from the microquasar v404 cygni during a recent period of strong flaring activity. the emission spectrum around 511 kiloelectronvolts shows clear signatures of variable positron annihilation, which implies a high rate of positron production. this supports the earlier conjecture that microquasars may be the main sources of the electron-positron plasma responsible for the bright diffuse emission of annihilation γ-rays in the bulge region of our galaxy. additionally, microquasars could be the origin of the observed megaelectronvolt continuum excess in the inner galaxy. | positron annihilation signatures associated with the outburst of the microquasar v404 cygni |
fundamental differences in the radio properties of red quasars (qsos), as compared to blue qsos, have been recently discovered, positioning them as a potential key population in the evolution of galaxies and black holes across cosmic time. to elucidate the nature of these objects, we exploited a rich compilation of broad-band photometry and spectroscopic data to model their spectral energy distributions (seds) from the ultraviolet to the far-infrared and characterise their emission-line properties. following a systematic comparison approach, we characterise the properties of the qso accretion, obscuration, and host galaxies in a sample of ∼1800 qsos at 0.2 < z < 2.5, classified into red and control qsos and matched in redshift and luminosity. we find no strong differences in the average multiwavelength seds of red and control qsos, other than the reddening of the accretion disk expected by the colour selection. additionally, no clear link can be recognised between the reddening of qsos and the interstellar medium as well as star formation properties of their host galaxies. our modelling of the infrared emission using dusty torus models suggests that the dust distributions and covering factors in red qsos are strikingly similar to those of the control sample, inferring that the reddening is not related to the torus and orientation effects. interestingly, we detect a significant excess of infrared emission at rest-frame 2−5 μm, which shows a direct correlation with optical reddening. to explain its origin, we investigated the presence of outflow signatures in the qso spectra, discovering a higher incidence of broad [o iii] wings and high c iv velocity shifts (> 1000 km s−1) in red qsos as compared to the control sample. we find that red qsos that exhibit evidence for high-velocity wind components present a stronger signature of the infrared excess, suggesting a causal connection between qso reddening and the presence of hot dust distributions in qso winds. we propose that dusty winds at nuclear scales are potentially the physical ingredient responsible for the optical colours in red qsos, as well as a key parameter for the regulation of accretion material in the nucleus. | the multiwavelength properties of red qsos: evidence for dusty winds as the origin of qso reddening |
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