abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
we search for ultraluminous quasi-stellar objects (qsos) at high redshift using photometry from the skymapper southern survey data release 3 (dr3), in combination with 2mass, vhs dr6, viking dr5, allwise, and catwise2020, as well as parallaxes and proper motions from gaia dr2 and edr3. we report 142 newly discovered southern qsos at 3.8 < z < 5.5, of which 126 have m145 < -27 ab mag and are found in a search area of 14 486 deg2. this southern sample, utilizing the gaia astrometry to offset wider photometric colour criteria, achieves unprecedented completeness for an ultraluminous qso search at high redshift. in combination with already known qsos, we construct a sample that is >80 per cent complete for m145 < -27.33 ab mag at z = 4.7 and for m145 < -27.73 ab mag at z = 5.4. we derive the bright end of the qso luminosity function at rest frame 145 nm for z = 4.7-5.4 and measure its slope to be β = -3.60 ± 0.37 and β = -3.38 ± 0.32 for two different estimates of the faint-end qso density adopted from the literature. we also present the first z ~ 5 qso luminosity function at rest frame 300 nm. | ultraluminous high-redshift quasars from skymapper - ii. new quasars and the bright end of the luminosity function |
we study the properties of strange quark matter (sqm) and quark stars (qss) in strong magnetic fields within the extended confined isospin-density-dependent mass (ciddm) model including the temperature dependence of the equivalent mass for quarks. the quark symmetry energy, quark symmetry free energy, and the equation of state (eos) of sqm in constant magnetic fields at finite temperature are investigated, and it is found that including the temperature dependence in ciddm model and considering strong magnetic fields can both significantly influence the properties of the sqm and the maximum mass of quark stars. using the density-dependent magnetic field and assuming two extreme cases for the magnetic field orientation in qss (the radial orientation in which the local magnetic fields are along the radial direction and the transverse orientation in which the local magnetic fields are randomly oriented but perpendicular to the radial orientation), we analyze the mass-radius relations for different stages of the protoquark stars (pqss) along the star evolution. our results indicate that the maximum mass of magnetized pqss may depend on not only the strength distribution and the orientation of the magnetic fields inside the pqss, but also the heating process and the cooling process in the star evolution. | quark matter and quark stars in strong magnetic fields at finite temperature within the confined-isospin-density-dependent mass model |
we report a definitive detection of chemically enriched cool gas around massive quiescent galaxies at z ≈ 0.4-0.7. the result is based on a survey of 37 621 luminous red galaxy (lrg)-quasi-stellar object pairs in sdss dr12 with projected distance d < 500 kpc. the lrgs are characterized by a predominantly old stellar population (age ≳ 1 gyr) with 13 per cent displaying [o ii] emission features and liner-like spectra. both passive and [o ii]-emitting lrgs share the same stellar mass distribution with a mean of <log (m*/m⊙)> ≈ 11.4 and a dispersion of 0.2 dex. both lrg populations exhibit associated strong mg ii absorbers out to d < 500 kpc. the mean gas covering fraction at d ≲ 120 kpc is < κ rangle _{mg ii} > 15 per cent and declines quickly to < κ rangle _{mg ii} ≈ 5 per cent at d ≲ 500 kpc. no clear dependence on stellar mass is detected for the observed mg ii absorption properties. the observed velocity dispersion of mg ii-absorbing gas relative to either passive or [o ii]-emitting lrgs is merely 60 per cent of what is expected from virial motion in these massive haloes. while no apparent azimuthal dependence is seen for < κ rangle _{mg ii} around passive lrgs at all radii, a modest enhancement in < κ rangle _{mg ii} is detected along the major axis of [o ii]-emitting lrgs at d < 50 kpc. the suppressed velocity dispersion of mg ii-absorbing gas around both passive and [o ii]-emitting lrgs, together with an elevated < κ rangle _{mg ii} along the major axis of [o ii]-emitting lrgs at d < 50 kpc, provides important insights into the origin of the observed chemically enriched cool gas in lrg haloes. we consider different scenarios and conclude that the observed mg ii absorbers around lrgs are best explained by a combination of cool clouds formed in thermally unstable lrg haloes and satellite accretion through filaments. | characterizing the chemically enriched circumgalactic medium of ∼38 000 luminous red galaxies in sdss dr12 |
the experiment for cryogenic large-aperture intensity mapping (exclaim) is a balloon-borne cryogenic telescope that will survey the spectrum of diffuse emission from both the milky way and the cosmic web to probe star formation, the interstellar medium, and galaxy evolution across cosmic time. exclaim's primary extragalactic science survey maps 305 deg2 along the celestial equator with an r = 512 spectrometer over the frequency range ν = 420 - 540 ghz, targeting emission of the [c ii] line over redshifts 2.5 < z < 3.5 and several co lines for z < 1. cross-correlation with galaxy redshift catalogues isolates line emission from the large-scale structure at target redshifts. in this paper, we forecast the sensitivity for both the two-point and conditional one-point cross-correlation. we predict that exclaim will detect both the [c ii]-qso cross-power spectrum and the conditional voxel intensity distribution (cvid) at various redshifts under a broad range of [c ii] intensity models, allowing it to differentiate among these models in the literature. these forecasts for the power spectra include the effects of line interlopers and continuum foreground contamination. we then convert the joint [c ii] constraints from both the cross-power spectrum and the cvid into constraints on the [c ii] halo luminosity-mass relation $l_\mathrm{[c\, \small {ii}]}(m)$ model parameters and the star formation rate density (sfrd) from [c ii] emission. we also develop sensitivity estimates for co, showing the ability to differentiate between models. | extragalactic science with the experiment for cryogenic large-aperture intensity mapping |
the radiation observed in quasars and active galactic nuclei is mainly produced by a relativistic plasma orbiting close to the black hole event horizon, where strong gravitational effects are relevant. the observational data of such systems can be compared with theoretical models to infer the black hole and plasma properties. in the comparison process, ray-tracing algorithms are essential to computing the trajectories followed by the photons from the source to our telescopes. in this paper, we present osiris: a new stable fortran code capable of efficiently computing null-geodesics around compact objects, including general relativistic effects such as gravitational lensing, redshift, and relativistic boosting. the algorithm is based on the hamiltonian formulation and uses different integration schemes to evolve null-geodesics while tracking the error in the hamiltonian constrain to ensure physical results. we found from an error analysis that the integration schemes are all stable, and the best one maintains an error below 10-11. particularly, to test the robustness and ability of the code to evolve geodesics in curved space-time, we compute the shadow and einstein rings of a kerr black hole with different rotation parameters and obtain the image of a thin keplerian accretion disk around a schwarzschild black hole. although osiris is parallelized neither with mpi nor with cuda, the computation times are of the same order as those reported by other codes with these types of parallel computing platforms. | osiris: a new code for ray tracing around compact objects |
we present a detailed study of two partial lyman limit systems (pllss) of neutral hydrogen column density $n_\mathrm{h\, i}\approx (1-3)\times 10^{16}\, \mathrm{cm}^{-2}$ discovered at $z$ = 0.5 in the cosmic ultraviolet baryon survey (cubs). available far-ultraviolet spectra from the hubble space telescope cosmic origins spectrograph and optical echelle spectra from mike on the magellan telescopes enable a comprehensive ionization analysis of diffuse circumgalactic gas based on resolved kinematics and abundance ratios of atomic species spanning five different ionization stages. these data provide unambiguous evidence of kinematically aligned multiphase gas that masquerades as a single-phase structure and can only be resolved by simultaneous accounting of the full range of observed ionic species. both systems are resolved into multiple components with inferred α-element abundance varying from [α/h] ≈-0.8 to near solar and densities spanning over two decades from log nh/cm-3 ≈ -2.2 to <-4.3. available deep galaxy survey data from the cubs program taken with vlt/muse, magellan/ldss3-c and magellan/imacs reveal that the $z$ = 0.47 system is located 55 kpc from a star-forming galaxy with prominent balmer absorption of stellar mass ${{m_{\rm star}}}\approx 2\times 10^{10}\, {{m_{\odot}}}$, while the $z$ = 0.54 system resides in an overdense environment of 11 galaxies within 750 kpc in projected distance, with the most massive being a luminous red galaxy of ${{m_{\rm star}}}\approx 2\times 10^{11}\, {{m_{\odot}}}$ at 375 kpc. the study of these two pllss adds to an emerging picture of the complex, multiphase circumgalactic gas that varies in chemical abundances and density on small spatial scales in diverse galaxy environments. the inhomogeneous nature of metal enrichment and density revealed in observations must be taken into account in theoretical models of diffuse halo gas. | the cosmic ultraviolet baryon survey (cubs) - iv. the complex multiphase circumgalactic medium as revealed by partial lyman limit systems |
accurate quasar classifications and redshift measurements are increasingly important to precision cosmology experiments. broad absorption line (bal) features are present in 15-20 per cent of all quasars, and these features can introduce systematic redshift errors, and in extreme cases produce misclassifications. we quantitatively investigate the impact of bal features on quasar classifications and redshift measurements with synthetic spectra that were designed to match observations by the dark energy spectroscopic instrument (desi) survey. over the course of 5 yr, desi aims to measure spectra for 40 million galaxies and quasars, including nearly three million quasars. our synthetic quasar spectra match the signal-to-noise ratio and redshift distributions of the first year of desi observations, and include the same synthetic quasar spectra both with and without bal features. we demonstrate that masking the locations of the bal features decreases the redshift errors by about 1 per cent and reduces the number of catastrophic redshift errors by about 80 per cent. we conclude that identifying and masking bal troughs should be a standard part of the redshift determination step for desi and other large-scale spectroscopic surveys of quasars. | analysis of the impact of broad absorption lines on quasar redshift measurements with synthetic observations |
we present the untimely catalog, a deep time-domain catalog of detections based on wide-field infrared survey explorer (wise) and neowise observations spanning the 2010 through 2020 time period. detections are extracted from "time-resolved unwise coadds," which stack together each biannual sky pass of wise imaging to create a set of ~16 all-sky maps (per band), each much deeper and cleaner than individual wise exposures. untimely incorporates the w1 (3.4 μm) and w2 (4.6 μm) channels, meaning that our data set effectively consists of ~32 full-sky unwise catalogs. we run the crowdsource crowded-field point-source photometry pipeline (schlafly et al. 2018) on each epochal coadd independently, with low detection thresholds: s/n = 4.0 (2.5) in w1 (w2). in total, we tabulate and publicly release 23.5 billion (19.9 billion) detections at w1 (w2). untimely is ~1.3 mag deeper than the wise/neowise single exposure source tables near the ecliptic, with further enhanced depth toward higher ecliptic latitudes. the untimely catalog is primarily designed to enable novel searches for faint, fast-moving objects, such as y dwarfs and/or late-type (t/y) subdwarfs in the milky way's thick disk or halo. untimely will also facilitate other time-domain science applications, such as all-sky studies of quasar variability at mid-infrared wavelengths over a decade-long time baseline. | untimely: a full-sky, time-domain unwise catalog |
we monitored bl lacertae for 13 nights in optical b, v, r, and i bands during 2014 october and november including quasi-simultaneous observations in v and r bands using two optical telescopes in india. we have studied multiband optical flux variations, colour variation and spectral changes in this blazar. source was found to be active during the whole monitoring period and showed significant intraday variability on three nights in v and r filters while displayed hints of variability on six other dates in r passband and on two nights in v filter. from the colour-magnitude analysis of the source, we found that the spectra of the target get flatter as it becomes brighter on intranight time-scale. using discrete correlation technique, we found that intraday light curves in both v and r filters are almost consistent and well correlated with each other. we also generated spectral energy distribution of the target using the b, v, r, and i data sets for all 13 nights which could help us investigate the physical process responsible for the observed variations in bl lacertae objects. we also discuss possible physical causes of the observed spectral variability. | multiband optical variability studies of bl lacertae |
we update the constraints on the cosmological parameters by adopting the planck data released in 2015 and baryon acoustic oscillation (bao) measurements including the new dr14 quasar sample measurement at redshift z=1.52, and we conclude that the six-parameter λ cdm model is preferred. exploring some extensions to the λ cdm model, we find that the equation of state of dark energy reads w=-1.036± 0.056 in the wcdm model, the effective number of relativistic degrees of freedom in the universe is n_ {eff}=3.09_{-0.20}^{+0.18} in the n_ {eff}+λ cdm model and the spatial curvature parameter is ω _k=(1.8± 1.9)× 10^{-3} in the ω _k+λ cdm model at 68% confidence level (c.l.), and the 95% c.l. upper bounds on the sum of three active neutrinos masses are \sum m_ν <0.16 ev for the normal hierarchy (nh) and \sum m_ν <0.19 ev for the inverted hierarchy (ih) with δ χ ^2≡ χ ^2_ {nh}-χ ^2_ {ih}=-1.25. | new cosmological constraints with extended-baryon oscillation spectroscopic survey dr14 quasar sample |
we investigate the triggering mechanism and the structural properties of obscured luminous active galactic nuclei from a detailed study of the rest-frame b and i hubble space telescope images of 29 nearby (z ≈ 0.04-0.4) optically selected type 2 quasars. morphological classification reveals that only a minority (34%) of the hosts are mergers or interacting galaxies. more than half (55%) of the hosts contain regular disks, and a substantial fraction (38%), in fact, are disk-dominated (b/t ≲ 0.2) late-type galaxies with low sérsic indices (n < 2), which is characteristic of pseudo bulges. the prevalence of bars in the spiral host galaxies may be sufficient to supply the modest fuel requirements needed to power the nuclear activity in these systems. nuclear star formation seems to be ubiquitous in the central regions, leading to positive color gradients within the bulges and enhancements in the central surface brightness of most systems. | the role of major mergers and nuclear star formation in nearby obscured quasars |
the [c ii] 158 μm fine-structure line is known to trace regions of active star formation and is the main coolant of the cold, neutral atomic medium. in this letter, we report a strong detection of the [c ii] line in the host galaxy of the brightest quasar known at z\gt 6.5, the pan-starrs1 selected quasar pso j036.5078+03.0498 (hereafter p036+03), using the iram noema millimeter interferometer. its [c ii] and total far-infrared luminosities are (5.8+/- 0.7)× {{10}9} {{l}⊙ } and (7.6+/- 1.5)× {{10}12} {{l}⊙ }, respectively. this results in an {{l}[c ii]}/{{l}tir} ratio of ∼ 0.8× {{10}-3}, which is at the high end of those found for active galaxies, though it is lower than the average found in typical main-sequence galaxies at z∼ 0. we also report a tentative additional line that we identify as a blended emission from the {{3}22}-{{3}13} and {{5}23}-{{4}32} h2o transitions. if confirmed, this would be the most distant detection of water emission to date. p036+03 rivals the current prototypical luminous j1148+5251 quasar at z = 6.42, in both rest-frame uv and [c ii] luminosities. given its brightness and because it is visible from both hemispheres (unlike j1148+5251), p036+03 has the potential of becoming an important laboratory for the study of star formation and of the interstellar medium only ∼800 myr after the big bang. based on observations carried out under project number e14ag with the iram noema interferometer. iram is supported by insu/cnrs (france), mpg (germany), and ign (spain). | bright [c ii] 158 μm emission in a quasar host galaxy at z = 6.54 |
we measure the location and energetics of a s iv balqso outflow. this outflow has a velocity of 10 800 km s-1 and a kinetic luminosity of 1045.7 erg s-1, which is 5.2 per cent of the eddington luminosity of the quasar. from collisional excitation models of the observed s iv/s iv* absorption troughs, we measure a hydrogen number density of n_h = 104.3 cm-3, which allows us to determine that the outflow is located 110 pc from the quasar. since s iv is formed in the same ionization phase as c iv, our results can be generalized to the ubiquitous c iv broad absorption lines (bals). our accumulated distance measurements suggest that observed bal outflows are located much farther away from the central source than is generally assumed (0.01-0.1 pc). | strong candidate for agn feedback: vlt/x-shooter observations of balqso sdss j0831+0354 |
the cosmic distance duality (cdd) relation (based on the etherington reciprocity theorem) plays a crucial role in a wide assortment of cosmological measurements. attempts at confirming it observationally have met with mixed results, though the general consensus appears to be that the data do support its existence in nature. a common limitation with past approaches has been their reliance on a specific cosmological model, or on measurements of the luminosity distance to type ia sne, which introduces a dependence on the presumed cosmology in spite of beliefs to the contrary. confirming that the cdd is actually realized in nature is crucial because its violation would require exotic new physics. in this paper, we study the cdd using the observed angular size of compact quasar cores and a gaussian process reconstruction of the h ii galaxy hubble diagram - without pre-assuming any particular background cosmology. in so doing, we confirm at a very high level of confidence that the angular-diameter and luminosity distances do indeed satisfy the cdd. we then demonstrate the potential power of this result by utilizing it in a comparative test of two competing cosmological models - the rh = ct universe and λcdm - and show that rh = ct is favoured by the cdd data with a likelihood {∼ } 82.3{{ per cent}} compared with {∼ } 17.7{{ per cent}} for the standard model. | a comparison of the rh = ct and λcdm cosmologies using the cosmic distance duality relation |
we analyse 1598 serendipitous chandra x-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude x-ray variability that is intrinsic to the quasar corona and innermost accretion flow. the quasars in this investigation are all spectroscopically confirmed, optically bright (mi ≤ 20.2), and contain no identifiable broad absorption lines in their optical/ultraviolet spectra. this sample includes quasars spanning z ≈ 0.1-4 and probes x-ray variability on time-scales of up to ≈12 rest-frame years. variability amplitudes are computed between every epoch of observation for each quasar and are analysed as a function of time-scale and luminosity. the tail-heavy distributions of variability amplitudes at all time-scales indicate that extreme x-ray variations are driven by an additional physical mechanism and not just typical random fluctuations of the coronal emission. similarly, extreme x-ray variations of low-luminosity quasars seem to be driven by an additional physical mechanism, whereas high-luminosity quasars seem more consistent with random fluctuations. the amplitude at which an x-ray variability event can be considered extreme is quantified for different time-scales and luminosities. extreme x-ray variations occur more frequently at long time-scales (δt ≳ 300 d) than at shorter time-scales and in low-luminosity quasars compared to high-luminosity quasars over a similar time-scale. a binomial analysis indicates that extreme intrinsic x-ray variations are rare, with a maximum occurrence rate of $\lt 2.4{{\ \rm per\ cent}}$ of observations. finally, we present x-ray variability and basic optical emission-line properties of three archival quasars that have been newly discovered to exhibit extreme x-ray variability. | the frequency of extreme x-ray variability for radio-quiet quasars |
the clustering properties of the universe at large scales are currently being probed at various redshifts through several cosmological tracers and with diverse statistical estimators. here we use the three-point angular correlation function (3pacf) to probe the baryon acoustic oscillation (bao) features in the quasars catalogue from the sloan digital sky survey data release 12, with mean redshift \overline{z} = 2.225, detecting the bao imprint with a statistical significance of 2.9 σ, obtained using lognormal mocks. following a quasi-model-independent approach for the 3pacf, we find the bao transversal signature for triangles with sides θ1 = 1.0° and θ2 = 1.5° and the angle between them of α = 1.59 ± 0.17 rad, a value that corresponds to the angular bao scale θ_bao=1.82° ± 0.21°, in excellent agreement with the value found in a recent work (θ_bao=1.77° ± 0.31°) applying the two-point angular correlation function (2pacf) to similar data. moreover, we performed two types of test: one to confirm the robustness of the bao signal in the 3pacf through random displacements in the data set, and the other to verify the suitability of our random samples, a null test that in fact does not show any signature that could bias our results. | baryon acoustic oscillations signature in the three-point angular correlation function from the sdss-dr12 quasar survey |
a popular recent approach to answering open-domain questions is to first search for question-related passages and then apply reading comprehension models to extract answers. existing methods usually extract answers from single passages independently. but some questions require a combination of evidence from across different sources to answer correctly. in this paper, we propose two models which make use of multiple passages to generate their answers. both use an answer-reranking approach which reorders the answer candidates generated by an existing state-of-the-art qa model. we propose two methods, namely, strength-based re-ranking and coverage-based re-ranking, to make use of the aggregated evidence from different passages to better determine the answer. our models have achieved state-of-the-art results on three public open-domain qa datasets: quasar-t, searchqa and the open-domain version of triviaqa, with about 8 percentage points of improvement over the former two datasets. | evidence aggregation for answer re-ranking in open-domain question answering |
context. the innermost regions in active galactic nuclei (agns) have not yet been spatially resolved, but spectropolarimetry can provide insight into their hidden physics and geometry. from spectropolarimetric observations in broad emission lines and assuming equatorial scattering as a dominant polarization mechanism, it is possible to estimate the mass of supermassive black holes (smbhs) residing at the center of agns.aims: we explore the possibilities and limits, and put constraints on the method for determining smbh masses using polarization in broad emission lines by providing more in-depth theoretical modeling.methods: we used the monte carlo radiative transfer code stokes to explore polarization properties of type-1 agns. we modeled equatorial scattering using flared-disk geometry for a set of different smbh masses assuming thomson scattering. in addition to the keplerian motion, which is assumed to be dominant in the broad-line region (blr), we also considered cases of additional radial inflows and vertical outflows.results: we modeled the profiles of polarization plane position angle φ, degree of polarization, and total unpolarized lines for different blr geometries and different smbh masses. our model confirms that the method can be widely used for type-1 agns when viewing inclinations are between 25° and 45°. we show that the distance between the blr and scattering region (sr) has a significant impact on the mass estimates and the best mass estimates are when the sr is situated at a distance 1.5-2.5 times larger than the outer blr radius.conclusions: our models show that if keplerian motion can be traced through the polarized line profile, then the direct estimation of the mass of the smbh can be performed. when radial inflows or vertical outflows are present in the blr, this method can still be applied if velocities of the inflow/outflow are less than 500 km s-1. we also find that models for ngc 4051, ngc 4151, 3c 273, and pg0844+349 are in good agreement with observations. | agn black hole mass estimates using polarization in broad emission lines |
as an important candidate gravity theory alternative to dark energy, a class of f(r) modified gravity, which introduces a perturbation of the ricci scalar r in the einstein-hilbert action, has been extensively applied to cosmology to explain the acceleration of the universe. in this paper, we focus on the recently-released vlbi observations of the compact structure in intermediate-luminosity quasars combined with the angular-diameter-distance measurements from galaxy clusters, which consists of 145 data points performing as individual cosmological standard rulers in the redshift range 0.023 <= z <= 2.80, to investigate observational constraints on two viable models in f(r) theories within the palatini formalism: f1(r) = r-a/rb and f2(r)=r-ar/r+ab. we also combine the individual standard ruler data with the observations of cmb and bao, which provides stringent constraints. furthermore, two model diagnostics, om(z) and statefinder, are also applied to distinguish the two f(r) models and λcdm model. our results show that (1) the quasars sample performs very well to place constraints on the two f(r) cosmologies, which indicates its potential to act as a powerful complementary probe to other cosmological standard rulers. (2) the λcdm model, which corresponds to b = 0 in the two f(r) cosmologies is still included within 1σ range. however, there still exists some possibility that λcdm may not the best cosmological model preferred by the current high-redshift observations. (3) given the current standard ruler data, the information criteria indicate that the cosmological constant model is still the best one, while the f1(r) model gets the smallest observational support. (4) the f2(r) model, which evolves quite different from f1(r) model at early times, still significantly deviates from both f1(r) and λcdm model at the present time. | a new test of f(r) gravity with the cosmological standard rulers in radio quasars |
we present an unprecedented view of the morphology and kinematics of the extended narrow-line region (enlr) and molecular gas around the prototypical hyperluminous quasar 3c 273 (l bol ∼ 1047 erg s-1 at z = 0.158) based on vlt-muse optical 3d spectroscopy and alma observations. we find the following: (1) the enlr size of 12.1 ± 0.2 kpc implies a smooth continuation of the size-luminosity relation out to large radii or a much larger break radius as previously proposed. (2) the kinematically disturbed ionized gas with line splits reaching 1000 km s-1 out to 6.1 ± 1.5 kpc is aligned along the jet axis. (3) the extreme line broadening on kiloparsec scales is caused by the spatial and spectral blending of many distinct gas clouds separated on subarcsecond scales by different line-of-sight (los) velocities. the enlr velocity field combined with the known jet orientation rules out a simple scenario of a radiatively driven radial expansion of the outflow. instead, we propose that a pressurized expanding hot gas cocoon created by the radio jet is impacting on an inclined gas disk, leading to transverse and/or backflow motion with respect to our los. the molecular gas morphology may be explained by either a density wave at the front of the outflow expanding along the jet direction as predicted by the positive feedback scenario or the cold gas may be trapped in a stellar overdensity caused by a recent merger event. using 3c 273 as a template for observations of high-redshift hyperluminous quasars reveals that large-scale enlrs and kiloparsec-scale outflows may often be missed, due to the brightness of the nuclei and the limited sensitivity of current near-ir instrumentation. | jet-driven galaxy-scale gas outflows in the hyperluminous quasar 3c 273 |
quasars at early redshifts (z > 6) with companion galaxies offer unique insights into the growth and evolution of the first supermassive black holes. here, we report on a 150 ks chandra observation of pso j308.0416-21.2339, a z = 6.23 quasar with a merging companion galaxy identified in [c ii] and rest-frame uv emission. with {72.3}-8.6+9.6 net counts, we find that pso j308.0416-21.2339 is powerful ({l}x={2.31}-0.76+1.14× {10}45 {erg} {{{s}}}-1 {cm}}-2 in rest-frame 2.0-10.0 kev) yet soft (spectral power-law index {{γ }}={2.39}-0.36+0.37 and optical-to-x-ray slope α ox = -1.41 ± 0.11). in addition, we detect three hard-energy photons 2.″0 to the west of the main quasar, cospatial with the brightest uv emission of the merging companion. as no soft-energy photons are detected in the same area, this is potentially indicative of a highly obscured source. with conservative assumptions, and accounting for both background fluctuations and the extended wings of the quasar’s emission, these photons only have a probability p = 0.021 of happening by chance. if confirmed by deeper observations, this system is the first high-redshift quasar and companion individually detected in x-rays and is likely a dual active galactic nucleus. | x-ray observations of a z ∼ 6.2 quasar/galaxy merger |
the dark energy spectroscopic instrument (desi) is a stage iv ground-based dark energy experiment planned to begin operations in 2020. in this article, we provided a short review of desi presented during the conference {\it recontres de moriond 2018}. desi will use four different tracers for mapping the universe: from redshift 0.05 up to redshift 1.7 with galaxies and from 2.1 to 3.5 using quasars. desi will measure a total of 35 million spectra covering regions of universe never explored before, providing a map of large scale structure that will enable major advances in the investigation of cosmic acceleration. the key science goals for desi are to constrain dark energy and potential deviations of general relativity using two complementary observables: the baryonic acoustic oscillations (bao) and the redshift space distortions (rsd). additional science goals, such as constraining the sum of neutrino masses and inflation, are expected with the baseline project. desi installation started on february 2018 and the current construction of the instrument is on track. the imaging surveys that will serve to determine the targets are currently in the final stages, having achieved 80\% completion, and are expected to be finalized by the end of 2018. the desi collaboration is actively preparing for survey operations and science analysis, to be ready for the first light in january 2020. | unraveling the universe with desi |
we develop a broad-band spectral model, agnslim, to describe super-eddington black hole accretion disc spectra. this is based on the slim disc emissivity, where radial advection keeps the surface luminosity at the local eddington limit, resulting in l(r) ∝ r-2 rather than the r-3 expected from the novikov-thorne (standard, sub-eddington) disc emissivity. wind losses should also be important but these are expected to produce a similar radiative emissivity. we assume that the flow is radially stratified, with an outer standard disc, an inner hot comptonizing region and an intermediate warm comptonizing region to produce the soft x-ray excess. this gives the model enough flexibility to fit the observed data, but with the additional requirement of energy conservation to give physical constraints. we use this to fit the broad-band spectrum of one of the most extreme active galactic nuclei, the narrow line seyfert 1 rx j0439.6-5311, which has a black hole mass of (6∼ 9)× 10^6 m_\odot as derived from the h β line width. this cannot be fit with the standard disc emissivity at this mass, as even zero spin models overproduce the observed luminosity. instead, we show that the spectrum is well reproduced by the slim disc model, giving mass accretion rates around (5 ∼ 10) × eddington limit. there is no constraint on black hole spin as the efficiency is reduced by advection. such extreme accretion rates should be characteristic of the first quasars, and we demonstrate this by fitting to the spectrum of a recently discovered super-eddington quasar, pso j006 + 39, at z = 6.6. | modelling the spectral energy distribution of super-eddington quasars |
we present the prospects of extracting information about the epoch of reionization by identifying the remaining neutral regions, referred to as islands, in tomographic observations of the redshifted 21-cm signal. using simulated data sets we show that at late times the 21-cm power spectrum is fairly insensitive to the details of the reionization process but that the properties of the neutral islands can distinguish between different reionization scenarios. we compare the properties of these islands with those of ionized bubbles. at equivalent volume-filling fractions, neutral islands tend to be fewer in number but larger compared to the ionized bubbles. in addition, the evolution of the size distribution of neutral islands is found to be slower than that of the ionized bubbles and also their percolation behaviour differs substantially. even though the neutral islands are relatively rare, they will be easier to identify in observations with the low frequency component of the square kilometre array due to their larger size and the lower noise levels at lower redshifts. the size distribution of neutral islands at the late stages of reionization is found to depend on the source properties, such as the ionizing efficiency of the sources and their minimum mass. we find the longest line of sight through a neutral region to be more than 100 comoving mpc until very late stages (90-95 per cent reionized), which may have relevance for the long absorption trough at z = 5.6-5.8 in the spectrum of quasar ulas j0148+0600. | neutral island statistics during reionization from 21-cm tomography |
previous, large samples of quasar absorption spectra have indicated some evidence for relative variations in the fine-structure constant (δα/α) across the sky. however, they were likely affected by long-range distortions of the wavelength calibration, so it is important to establish a statistical sample of more reliable results from multiple telescopes. here we triple the sample of δα/α measurements from the subaru telescope which have been `supercalibrated' to correct for long-range distortions. a blinded analysis of the metallic ions in six intervening absorption systems in two subaru quasar spectra provides no evidence for α variation, with a weighted mean of δα/α = 3.0 ± 2.8stat ± 2.0sys parts per million (1σ statistical and systematic uncertainties). the main remaining systematic effects are uncertainties in the long-range distortion corrections, absorption profile models, and errors from redispersing multiple quasar exposures on to a common wavelength grid. the results also assume that terrestrial isotopic abundances prevail in the absorbers; assuming only the dominant terrestrial isotope is present significantly lowers δα/α, though it is still consistent with zero. given the location of the two quasars on the sky, our results do not support the evidence for spatial α variation, especially when combined with the 21 other recent measurements which were corrected for, or resistant to, long-range distortions. our spectra and absorption profile fits are publicly available. | subaru telescope limits on cosmological variations in the fine-structure constant |
we present a detailed multiwavelength study of an unobscured, highly super-eddington type-1 qso rx j0439.6-5311. we combine the latest xmm-newton observation with all archival data from infrared to hard x-rays. the optical spectrum is very similar to that of 1h 0707-495 in having extremely weak [o iii] and strong fe ii emission lines, although the black hole mass is probably slightly higher at 5-10 × 106 m⊙. the broad-band spectral energy distribution is uniquely well defined due to the extremely low galactic and intrinsic absorption, so the bolometric luminosity is tightly constrained. the optical/uv accretion disc continuum is seen down to 900 å, showing that there is a standard thin disc structure down to r ≥ 190-380 rg and determining the mass accretion rate through the outer disc. this predicts a much higher bolometric luminosity than observed, indicating that there must be strong wind and/or advective energy losses from the inner disc, as expected for a highly super-eddington accretion flow. significant outflows are detected in both the narrow-line region (nlr) and broad-line region (blr) emission lines, confirming the presence of a wind. we propose a global picture for the structure of a super-eddington accretion flow where the inner disc puffs up, shielding much of the potential nlr material, and show how inclination angle with respect to this and the wind can explain very different x-ray properties of rx j0439.6-5311 and 1h 0707-495. therefore, this source provides strong supporting evidence that 'simple' and 'complex' super-eddington nls1s can be unified within the same accretion flow scenario but with different inclination angles. we also propose that these extreme nls1s could be the low-redshift analogues of weak emission-line quasars. | super-eddington qso rx j0439.6-5311 - ii. multiwavelength constraints on the global structure of the accretion flow |
in this paper, we analyze the implications of the latest cosmological data sets to test the etherington distance duality relation (ddr), which connects the luminosity distance dl and angular diameter distance da at the same redshift. for dl, we consider the simulated data of gravitational waves from the third-generation gravitational wave detector [the einstein telescope (et)], which can be considered as standard candles (or standard siren), while the angular diameter distances da are derived from the newly compiled sample of compact radio quasars observed by very-long-baseline interferometry (vlbi), which represents a new type of cosmological standard ruler. alleviating the absorbtion and scattering effects of dust in the universe, this will create a valuable opportunity to directly test ddr at much higher precision with the combination of gravitational wave (gw) and electromagnetic (em) signals. our results show that, with the combination of the current radio quasar observations, the duality-distance relation can be verified at the precision of 10-2. moreover, the einstein telescope would produce more robust constraints on the validity of such distance duality relation (at the precision of 10-3), with a larger sample of compact milliarcsecond radio quasars detected in future vlbi surveys. | testing the etherington distance duality relation at higher redshifts: combined radio quasar and gravitational wave data |
context. soft and hard x-ray excesses, compared to the continuum power-law shape between ∼2−10 kev, are common features observed in the spectra of active galactic nuclei (agn) and are associated with the accretion disc-corona system around the supermassive black hole. however, the dominant process at work is still highly debated and has been proposed to be either relativistic reflection or comptonisation. such an investigation can be problematic for agn that have significant intrinsic absorption, either cold or warm, which can severely distort the observed continuum. therefore, agn with no (or very weak) intrinsic absorption along the line-of-sight, called bare agn, are the best targets for directly probing disc-corona systems.aims: we aim to characterise the main x-ray spectral physical components from the bright bare broad-line seyfert 1 agn mrk 110, as well as the physical process(es) at work in its disc-corona system viewed almost face-on.methods: we perform the x-ray broadband spectral analysis thanks to two simultaneous xmm-newton and nustar observations performed on november 16−17, 2019, and april 5−6, 2020. we also use a deep nustar observation obtained in january 2017 for the spectral analysis above 3 kev.results: the broadband x-ray spectra of mrk 110 are characterised by the presence of a prominent and absorption-free smooth soft x-ray excess, moderately broad o vii and fe kα emission lines, and a lack of a strong compton hump. the continuum above ∼3 kev is very similar at both epochs, while some variability (stronger when brighter) is present for the soft x-ray excess. a combination of soft and hard comptonisation by a warm and hot corona, respectively, plus mildly relativistic disc reflection reproduce the broadband x-ray continuum very well. the inferred warm corona temperature, ktwarm ∼ 0.3 kev, is similar to the values found in other sub-eddington agn, whereas the hot corona temperature, kthot ∼ 21−31 kev (depending mainly on the assumed hot corona geometry), is found to be in the lower range of the values measured in agn. | the first simultaneous x-ray broadband view of mrk 110 with xmm-newton and nustar |
we are compiling a new list of gamma-ray jetted active galactic nuclei (agn), starting from the fourth catalog of point sources of the fermi large area telescope (lat). our aim is to prepare a list of jetted agn with known redshifts and classifications to be used to calibrate jet power. we searched in the available literature for all the published optical spectra and multiwavelength studies useful to characterize the sources. we found new, missed, or even forgotten information leading to a substantial change in the redshift values and classification of many sources. we present here the preliminary results of this analysis and some statistics based on the gamma-ray sources with right ascension within the interval 0 h – 12 h (j2000). although flat-spectrum radio quasars and bl lac objects are still the dominant populations, there is a significant increase in the number of other objects, such as misaligned agn, narrow-line seyfert 1 galaxies, and seyfert galaxies. we also introduced two new classes of objects: changing-look agn and ambiguous sources. about one third of the sources remain unclassified. | a new sample of gamma-ray emitting jetted active galactic nuclei—preliminary results |
we identify 885,503 type 1 quasar candidates to i≲ 22 using the combination of optical and mid-ir photometry. optical photometry is taken from the sloan digital sky survey-iii: baryon oscillation spectroscopic survey (sdss-iii/boss), while mid-ir photometry comes from a combination of data from the wide-field infrared survey explorer (wise) “allwise” data release and several large-area spitzer space telescope fields. selection is based on a bayesian kernel density algorithm with a training sample of 157,701 spectroscopically confirmed type 1 quasars with both optical and mid-ir data. of the quasar candidates, 733,713 lack spectroscopic confirmation (and 305,623 are objects that we have not previously classified as photometric quasar candidates). these candidates include 7874 objects targeted as high-probability potential quasars with 3.5\lt z\lt 5 (of which 6779 are new photometric candidates). our algorithm is more complete to z\gt 3.5 than the traditional mid-ir selection “wedges” and to 2.2\lt z\lt 3.5 quasars than the sdss-iii/boss project. number counts and luminosity function analysis suggest that the resulting catalog is relatively complete to known quasars and is identifying new high-z quasars at z\gt 3. this catalog paves the way for luminosity-dependent clustering investigations of large numbers of faint, high-redshift quasars and for further machine-learning quasar selection using spitzer and wise data combined with other large-area optical imaging surveys. | bayesian high-redshift quasar classification from optical and mid-ir photometry |
the physics and demographics of type 2 quasars remain poorly understood, and new samples of such objects selected in a variety of ways can give insight into their physical properties, evolution, and relationship to their host galaxies. we present a sample of 2758 type 2 quasars at z ≲ 1 from the sloan digital sky survey-iii (sdss-iii)/baryon oscillation spectroscopic survey (boss) spectroscopic data base, selected on the basis of their emission-line properties. we probe the luminous end of the population by requiring the rest-frame equivalent width of [o iii] to be >100 å. we distinguish our objects from star-forming galaxies and type 1 quasars using line widths, standard emission line ratio diagnostic diagrams at z < 0.52 and detection of [ne v]λ3426 å at z > 0.52. the majority of our objects have [o iii] luminosities in the range 1.2 × 1042-3.8 × 1043 erg s-1 and redshifts between 0.4 and 0.65. our sample includes over 400 type 2 quasars with incorrectly measured redshifts in the boss data base; such objects often show kinematic substructure or outflows in the [o iii] line. the majority of the sample has counterparts in the wide-field infrared survey explorer survey, with median infrared luminosity νlν[12 μm] = 4.2 × 1044 erg s- 1. only 34 per cent of the newly identified type 2 quasars would be selected by infrared colour cuts designed to identify obscured active nuclei, highlighting the difficulty of identifying complete samples of type 2 quasars. we make public the multi-gaussian decompositions of all [o iii] profiles for the new sample and for 568 type 2 quasars from sdss i/ii, together with non-parametric measures of the [o iii] line profile shapes. we also identify over 600 candidate double-peaked [o iii] profiles. | spectroscopic identification of type 2 quasars at z < 1 in sdss-iii/boss |
we analyze the optical, uv, and x-ray microlensing variability of the lensed quasar sdss j0924+0219 using six epochs of chandra data in two energy bands (spanning 0.4-8.0 kev, or 1-20 kev in the quasar rest frame), 10 epochs of f275w (rest-frame 1089 å) hubble space telescope data, and high-cadence r-band (rest-frame 2770 å) monitoring spanning 11 years. our joint analysis provides robust constraints on the extent of the x-ray continuum emission region and the projected area of the accretion disk. the best-fit half-light radius of the soft x-ray continuum emission region is between 5× {10}13 and 1015 cm, and we find an upper limit of 1015 cm for the hard x-rays. the best-fit soft-band size is about 13 times smaller than the optical size, and roughly 7{{gm}}{bh}/{c}2 for a 2.8× {10}8 {m}⊙black hole, similar to the results for other systems. we find that the uv emitting region falls in between the optical and x-ray emitting regions at 1014 cm \lt {r}1/2,{uv}\lt 3× {10}15 cm. finally, the optical size is significantly larger, by 1.5σ, than the theoretical thin-disk estimate based on the observed, magnification-corrected i-band flux, suggesting a shallower temperature profile than expected for a standard disk. | a consistent picture emerges: a compact x-ray continuum emission region in the gravitationally lensed quasar sdss j0924+0219 |
we present new observations acquired with the multi unit spectroscopic explorer instrument on the very large telescope in a quasar field that hosts a high column density damped lyα absorber (dla) at z ≈ 3.25. we detect lyα emission from a nebula at the redshift of the dla with line luminosity (27 ± 1) × 1041 erg s- 1, which extends over 37 ± 1 kpc above a surface brightness limit of 6 × 10-19 erg s- 1 cm- 2 arcsec- 2 at a projected distance of 30.5 ± 0.5 kpc from the quasar sightline. two clumps lie inside this nebula, both with lyα rest-frame equivalent width > 50 å and with relative line-of-sight velocities aligned with two main absorption components seen in the dla spectrum. in addition, we identify a compact galaxy at a projected distance of 19.1 ± 0.5 kpc from the quasar sightline. the galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the dla redshift. we argue that the lyα nebula is ionized by radiation from star formation inside the two clumps, or by radiation from the compact galaxy. in either case, these data imply the presence of a structure with size ≫50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the eagle simulations. | witnessing galaxy assembly in an extended z≈3 structure |
we investigate the performance of different methodologies that measure the time lag between broad-line and continuum variations in reverberation mapping data using simulated light curves that probe a range of cadence, time baseline, and signal-to-noise ratio in the flux measurements. we compare three widely adopted lag-measuring methods: the interpolated cross-correlation function (iccf), the z-transformed discrete correlation function (zdcf), and the markov chain monte carlo code javelin, for mock data with qualities typical of multiobject spectroscopic reverberation mapping (mos-rm) surveys that simultaneously monitor hundreds of quasars. we quantify the overall lag-detection efficiency, the rate of false detections, and the quality of lag measurements for each of these methods and under different survey designs (e.g., observing cadence and depth) using mock quasar light curves. overall javelin and iccf outperform zdcf in essentially all tests performed. compared with iccf, javelin produces higher quality lag measurements, is capable of measuring more lags with timescales shorter than the observing cadence, is less susceptible to seasonal gaps and signal-to-noise ratio degradation in the light curves, and produces more accurate lag uncertainties. we measure the hβ broad-line region size-luminosity (r-l) relation with each method using the simulated light curves to assess the impact of selection effects of the design of mos-rm surveys. the slope of the r-l relation measured by javelin is the least biased among the three methods and is consistent across different survey designs. these results demonstrate a clear preference for javelin over the other two nonparametric methods for mos-rm programs, particularly in the regime of limited light-curve quality as expected from most mos-rm programs. | the sloan digital sky survey reverberation mapping project: comparison of lag measurement methods with simulated observations |
the discovery of multiply-imaged gravitationally lensed qsos is fundamental to many astronomical and cosmological studies. however, these objects are rare and challenging to discover due to requirements of high-angular resolution astrometric, multiwavelength photometric and spectroscopic data. this has limited the number of known systems to a few hundred objects. we aim to reduce the constraints on angular resolution and discover multiply-imaged qso candidates by using new candidate selection principles based on unresolved photometric time-series and ground-based images from public surveys. we selected candidates for multiply-imaged qsos based on low levels of entropy computed from catalina unresolved photometric time-series or euclidean similarity to known lenses in a space defined by the wavelet power spectra of pan-starss dr2 or decals dr7 images, combined with multiple {\it gaia} dr2 sources or large astrometric errors and supervised and unsupervised learning methods. we then confirmed spectroscopically some candidates with the palomar hale, keck-i, and eso/ntt telescopes. here we report the discovery and confirmation of seven doubly-imaged qsos and one likely double quasar. this demonstrates the potential of combining space-astrometry, even if unresolved, with low spatial-resolution photometric time-series and/or low-spatial resolution multi-band imaging to discover multiply-imaged lensed qsos. | gaia gral: gaia dr2 gravitational lens systems. v. doubly-imaged qsos discovered from entropy and wavelets |
we present e-merlin and european vlbi network observations which reveal unambiguous jet activity within radio-quiet quasar hs 0810+2554. with an intrinsic flux density of 880 njy, this is the faintest radio source ever imaged. the findings present new evidence against the idea that radio-loud and radio-quiet quasars are powered by different underlying radio emission mechanisms, showing instead that the same active galactic nucleus (agn) mechanism can operate as the dominant source of radio emission even in the very lowest radio luminosity quasars. due to strong gravitational lensing, our source is not only visible, but with vlbi is imaged to a scale of just 0.27 pc: the highest ever resolution image of a radio-quiet quasar. brightness temperatures of at least 8.4 × 106 k are associated with two highly compact components. subsequent modelling of the lensed system has revealed that the components are linearly aligned on opposing sides of the optical quasar core, with the typical morphology of a compact symmetric object (cso). given that this source has been found to fall on the radio-fir correlation, we suggest that the radio-fir correlation cannot always be used to rule out agn activity in favour of star formation activity. the correlation - or at least its scatter - may conceal the coexistence of kinetic and radiative feedback modes in agn. modelling of the lensing mass itself points to a non-smooth mass distribution, hinting at the presence of dark matter substructure which has manifested as astrometric perturbations of the vlbi lensed images. | strong lensing reveals jets in a sub-microjy radio-quiet quasar |
we analyze relative abundances and ionization conditions in a strong absorption system at z=6.84, seen in the spectrum of the z=7.54 background quasar ulas j134208.10+092838.61. singly ionized c, si, fe, mg, and al measurements are consistent with a warm neutral medium that is metal-poor but not chemically pristine. firm non-detections of c iv and si iv imply that any warm ionized phase of the igm or cgm has not yet been enriched past the ultra-metal-poor regime (<0.001z_{solar}), unlike lower redshift dlas where these lines are nearly ubiquitous. relative abundances of the heavy elements 794 myr after the big bang resemble those of metal-poor damped lyman alpha systems at intermediate redshift and milky way halo stars, and show no evidence of enhanced [alpha/fe], [c/fe] or other signatures of yields dominated by massive stars. a detection of the cii* fine structure line reveals local sources of excitation from heating, beyond the level of photo-excitation supplied by the cmb. we estimate the total and [cii] cooling rates, balancing against ism heating sources to develop an heuristic two-phase model of the neutral medium. the implied heating requires a surface density of star formation slightly exceeding that of the milky way but not at the level of a strong starburst. for a typical (assumed) nhi=10^{20.6}, an abundance of [fe/h]=-2.2 matches the columns of species in the neutral phase. to remain undetected in c iv, a warm ionized phase would either need much lower [c/h]<-4.2 over an absorption path of 1 kpc, or else a very small absorption path (a few pc). while still speculative, these results suggest a significant reduction in heavy element enrichment outside of neutral star forming regions of the ism, as would be expected in early stages of galactic chemical evolution. | interstellar and circumgalactic properties of an unseen $z=6.84$ galaxy: abundances, ionization, and heating in the earliest known quasar absorber |
on july 30th, 2019 icecube detected a high-energy astrophysical muon neutrino candidate, ic-190730a with a 67% probability of astrophysical origin. the flat spectrum radio quasar (fsrq) pks 1502 +106 is in the error circle of the neutrino. motivated by this observation, we study pks 1502+106 as a possible source of ic-190730a. pks 1502+106 was in a quiet state in terms of uv/optical/x-ray/γ-ray flux at the time of the neutrino alert, we therefore model the expected neutrino emission from the source during its average long-term state, and investigate whether the emission of ic-190730a as a result of the quiet long-term emission of pks 1502+106 is plausible. we analyse uv/optical and x-ray data and collect additional observations from the literature to construct the multi-wavelength spectral energy distribution of pks 1502+106. we perform leptohadronic modelling of the multi-wavelength emission of the source and determine the most plausible emission scenarios and the maximum expected accompanying neutrino flux. a model in which the multi-wavelength emission of pks 1502+106 originates beyond the broad-line region and inside the dust torus is most consistent with the observations. in this scenario, pks 1502+106 can have produced up to of order one muon neutrino with energy exceeding 100 tev in the lifetime of icecube. an appealing feature of this model is that the required proton luminosity is consistent with the average required proton luminosity if blazars power the observed ultra-high-energy-cosmic-ray flux and well below the source's eddington luminosity. if such a model is ubiquitous among fsrqs, additional neutrinos can be expected from other bright sources with energy ≳ 10 pev. | multi-messenger emission from the parsec-scale jet of the flat-spectrum radio quasar pks 1502+106 coincident with high-energy neutrino icecube-190730a |
we compare two state-of-the-art numerical codes to study the overall accuracy in modelling the intergalactic medium and reproducing lyman-α forest observables for desi and high-resolution data sets. the codes employ different approaches to solving both gravity and modelling the gas hydrodynamics. the first code, nyx, solves the poisson equation using the particle-mesh (pm) method and the euler equations using a finite-volume method. the second code, crk-hacc , uses a tree-pm method to solve for gravity, and an improved lagrangian smoothed particle hydrodynamics (sph) technique, where fluid elements are modelled with particles, to treat the intergalactic gas. we compare the convergence behaviour of the codes in flux statistics as well as the degree to which the codes agree in the converged limit. we find good agreement overall with differences being less than observational uncertainties, and a particularly notable ≲1 per cent agreement in the 1d flux power spectrum. this agreement was achieved by applying a tessellation methodology for reconstructing the density in crk-hacc instead of using an sph kernel as is standard practice. we show that use of the sph kernel can lead to significant and unnecessary biases in flux statistics; this is especially prominent at high redshifts, z ~ 5, as the lyman-α forest mostly comes from lower-density regions that are intrinsically poorly sampled by sph particles. | modelling the lyman-α forest with eulerian and sph hydrodynamical methods |
context. one of the novelties of gaia data release 3 (dr3) with respect to the previous data releases is the publication of the multiband light curves for about 1 million active galactic nuclei (agn) and of the values of some parameters characterising their variability properties.aims: the goal of this work is the creation of a catalogue of variable agn, the selection of which is based on gaia data only.methods: we first present the implementation of the methods used to estimate the variability parameters within the framework of a specific object study module for agn (sos-agn). we then describe the selection procedure that led to the definition of the high-purity gaia variable agn sample and analyse the properties of the selected sources. we started from a sample of millions of sources, which were identified as agn candidates using 11 different classifiers based on variability processing. because the focus is on the variability properties, we first defined some pre-requisites in terms of number of data points in the g band and mandatory variability parameters. a series of filters was then applied using only gaia data and the gaia celestial reference frame 3 (gaia-crf3) sample as a reference.results: the resulting gaia agn variable sample, named glean, contains about 872 000 objects, more than 21 000 of which are new identifications. we checked for the presence of contaminants by cross-matching the selected sources with a variety of galaxies and stellar catalogues. the completeness of glean with respect to the variable agn in the last sloan digital sky survey (sdss) quasar catalogue is ∼47%, while that based on the variable agn of the gaia-crf3 sample is ∼51%. the set of filters applied to the sources selected by sos-agn to increase the sample purity reduced the source number by about 37%. from both a comparison with other agn catalogues and an investigation of possible contaminants, we conclude that purity can be expected to be above 95%. the multi-wavelength properties of these sources are investigated. in particular, we estimate that ∼4% of them are radio-loud. we finally explore the possibility to evaluate the time-lags between the flux variations of the multiple images of strongly lensed quasars, and show one case. | gaia data release 3. the first gaia catalogue of variable agn |
we explore the extinction/reddening of ∼35,000 uniformly selected quasars with 0\lt z≤slant 5.3 in order to better understand their intrinsic optical/ultraviolet (uv) spectral energy distributions. using rest-frame optical-uv photometry taken from the sloan digital sky survey’s (sdss) 7th data release, cross-matched to wise in the mid-infrared, 2mass and ukidss in the near-infrared, and galex in the uv, we isolate outliers in the color distribution and find them well described by an smc-like reddening law. a hierarchical bayesian model with a markov chain monte carlo sampling method was used to find distributions of power law indices and e(b-v) consistent with both the broad absorption line (bal) and non-bal samples. we find that, of the ugriz color-selected type 1 quasars in sdss, 2.5% (13%) of the non-bal (bal) sample are consistent with e(b-v)\gt 0.1 and 0.1% (1.3%) with e(b-v)\gt 0.2. simulations show both populations of quasars are intrinsically bluer than the mean composite, with a mean spectral index ({{α }λ }) of -1.79 (-1.83). the emission and absorption-line properties of both samples reveal that quasars with intrinsically red continua have narrower balmer lines and stronger high-ionization emission lines, the latter indicating a harder continuum in the extreme-uv and the former pointing to differences in black hole mass and/or orientation. | mining for dust in type 1 quasars |
we identify sources with extremely hard x-ray spectra (i.e., with photon indices of {{γ }}≲ 0.6) in the 13 deg2 nustar serendipitous survey, to search for the most highly obscured active galactic nuclei (agns) detected at > 10 {kev}. eight extreme nustar sources are identified, and we use the nustar data in combination with lower-energy x-ray observations (from chandra, swift xrt, and xmm-newton) to characterize the broadband (0.5-24 kev) x-ray spectra. we find that all of the extreme sources are highly obscured agns, including three robust compton-thick (ct; {n}{{h}}> 1.5× {10}24 cm-2) agns at low redshift (z< 0.1) and a likely ct agn at higher redshift (z = 0.16). most of the extreme sources would not have been identified as highly obscured based on the low-energy (< 10 kev) x-ray coverage alone. the multiwavelength properties (e.g., optical spectra and x-ray-mid-ir luminosity ratios) provide further support for the eight sources being significantly obscured. correcting for absorption, the intrinsic rest-frame 10-40 kev luminosities of the extreme sources cover a broad range, from ≈ 5× {10}42 to 1045 erg s-1. the estimated number counts of ct agns in the nustar serendipitous survey are in broad agreement with model expectations based on previous x-ray surveys, except for the lowest redshifts (z< 0.07), where we measure a high ct fraction of {f}{ct}{obs}={30}-12+16 % . for the small sample of ct agns, we find a high fraction of galaxy major mergers (50% ± 33%) compared to control samples of “normal” agns. | the nustar serendipitous survey: hunting for the most extreme obscured agn at >10 kev |
blazars are a class of active galactic nuclei that host relativistic jets oriented close to the observer's line of sight. blazars have very complex variability properties. flares, namely flux variations around the mean value with a well-defined shape and duration, are one of the identifying properties of the blazar phenomenon. blazars are known to exhibit multiwavelength flares, but also "orphan" flares, namely flux changes that appear only in a specific energy range. various models, sometimes at odds with each other, have been proposed to explain specific flares even for a single source, and cannot be synthesized into a coherent picture. in this paper, we propose a unified model for explaining orphan and multiwavelength flares from blazars in a common framework. we assume that the blazar emission during a flare consists of two components: (i) a quasistable component that arises from the superposition of numerous but comparatively weak dissipation zones along the jet, forming the background (low-state) emission of the blazar, and (ii) a transient component, which is responsible for the sudden enhancement of the blazar flux, forming at a random distance along the jet by a strong energy dissipation event. whether a multiwavelength or orphan flare is emitted depends on the distance from the base of the jet where the dissipation occurs. generally speaking, if the dissipation occurs at a small/large distance from the supermassive black hole, the inverse compton/synchrotron radiation dominates and an orphan γ -ray/optical flare tends to appear. on the other hand, we may expect a multiwavelength flare if the dissipation occurs at an intermediate distance. we show that the model can successfully describe the spectral energy distribution of different flares from the flat spectrum radio quasar 3c 279 and the bl lacertae object pks 2155-304. | unified model for orphan and multiwavelength blazar flares |
in this work, we consider static quark star (qs) within the framework of rastall gravity. rastall gravity purports to be the nonconservative theory of gravity and an unusual nonminimal coupling between matter and geometry. in our study, we consider a quantum chromodynamics (qcd)-motivated equation of state (eos) to determine the properties of qss in rastall gravity. depending on the values of parameters, we seek to determine the mass-radius relations for qss in rastall gravity, identifying the deviation from standard general relativity (gr) counterparts. interestingly, we find the value of the maximum gravitational mass to be more than 2m⊙ for the given equation of state (eos). we present the essential features regarding the stability of qss. | possible existence of quark stars in rastall gravity |
we analyze a complete spectroscopic sample of galaxies ( 600 000) drawn from sloan digital sky survey (sdss, dr7) to look for evidence of galactic winds in the local universe. we focus on the shape of the [oiii]λ5007 emission line as a tracer of ionizing gas outflows. we stack our spectra in a fine grid of star formation rate (sfr) and stellar mass to analyze the dependence of winds on the position of galaxies in the sfr versus mass diagram. we do not find any significant evidence of broad and shifted [oiii]λ5007 emission line which we interpret as no evidence of outflowing ionized gas in the global population. we have also classified these galaxies as star-forming or agn-dominated according to their position in the standard bpt diagram. we show how the average [oiii]λ5007 profile changes as a function of the nature of the dominant ionizing source. we find that in the star-forming dominated source the oxygen line is symmetric and governed by the gravitational potential well. the agn or composite agn/star-formation activity objects, in contrast, display a prominent and asymmetric profile that can be well described by a broad gaussian component that is blue-shifted from a narrow symmetric core. in particular, we find that the blue wings of the average [oiii]λ5007 profiles are increasingly prominent in the liners and seyfert galaxies. we conclude that, through the identification of strong bulk motion as traced by the warm ionized gas, in the low-redshift universe, "pure" star-formation activity does not seem capable of driving ionized-gas outflows, while, the presence of optically selected agn seems to play a primary role. we discuss the implications of these results for the role of the quenching mechanism in the present-day universe. | light breeze in the local universe |
we provide constraints on possible configurations and interactions of two coplanar tori orbiting a central kerr black hole (bh), in dependence on its dimensionless spin. the two-tori configurations can be directly linked to the current models featuring the obscuration of galactic bh x-ray emission. the emergence of each torus instability phases is discussed and tori collision has been also investigated. the first simple evaluation of the center-of-mass energy proves that collision-energy-efficiency increases with the dimensionless bh spin. we explore the phenomenological aspects of the corotating and counterrotating tori by analyzing properties of the orbiting toroidal configurations related to the fluid enthalpy flux, the mass-flux, the mass-accretion-rates, and the cusp luminosity in the two cases of corotating and counterrotating fluids in dependence on the smbh spin. the analysis resulted ultimately in a comparative investigation of the properties of corotating versus counterrotating tori, demonstrating that two accretion tori can orbit around the central kerr attractor only under very specific conditions. our results also demonstrate that the dynamics of the unstable phases of these double tori systems is significant for the high energy phenomena which could be observable in the x-ray emission and extremely energetic phenomena in active galactic nuclei and quasar. | rads energetics and constraints on emerging tori collisions around super-massive kerr black holes |
aims: we present and study spatially resolved imaging obtained with the atacama large millimeter/submillimeter array (alma) of multiple 12co(j = 6 - 5, 8-7, and 9-8) and two h2o(202-111 and 211-202) emission lines and cold dust continuum toward the gravitationally lensed dusty star-forming galaxy spt 0346-52 at z = 5.656.methods: using a visibility-domain source-plane reconstruction we probe the structure and dynamics of the different components of the interstellar medium (ism) in this galaxy down to scales of 1 kpc in the source plane.results: measurements of the intrinsic sizes of the different co emission lines indicate that the higher j transitions trace more compact regions in the galaxy. similarly, we find smaller dust continuum intrinsic sizes with decreasing wavelength, based on observations at rest frame 130, 300, and 450 μm. the source shows significant velocity structure, and clear asymmetry where an elongated structure is observed in the source plane with significant variations in their reconstructed sizes. this could be attributed to a compact merger or turbulent disk rotation. the differences in velocity structure through the different line tracers, however, hint at the former scenario in agreement with previous [cii] line imaging results. measurements of the co line ratios and magnifications yield significant variations as a function of velocity, suggesting that modeling of the ism using integrated values could be misinterpreted. modeling of the ism in spt 0346-52 based on delensed fluxes indicates a highly dense and warm medium, qualitatively similar to that observed in high-redshift quasar hosts. a copy of the reduced datacubes is available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/628/a23 | imaging the molecular interstellar medium in a gravitationally lensed star-forming galaxy at z = 5.7 |
we present observed mid-infrared and optical colors and composite spectral energy distributions (seds) of type 1 (broad-line) and 2 (narrow-line) quasars selected from sloan digital sky survey (sdss) spectroscopy. a significant fraction of powerful quasars are obscured by dust and are difficult to detect in optical photometric or spectroscopic surveys. however, these may be more easily identified on the basis of mid-infrared (mir) colors and seds. using samples of sdss type 1 and 2 matched in redshift and [o iii] luminosity, we produce composite rest-frame 0.2-15 μm seds based on sdss, ukidss, and wide-field infrared survey explorer photometry and perform model fits using simple galaxy and quasar sed templates. the seds of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. for both types of quasar, the flux of the active galactic nucleus (agn) relative to the host galaxy increases with agn luminosity ({l}[{{o}{{iii}}]}) and redder observed mir color, but we find only weak dependencies of the composite seds on mechanical jet power as determined through radio luminosity. we conclude that luminous quasars can be effectively selected using simple mir color criteria similar to those identified previously ({{w}}1{--}{{w}}2> 0.7; vega), although these criteria miss many heavily obscured objects. obscured quasars can be further identified based on optical-ir colors (for example, (u{--}{{w}}3 [{ab}])> 1.4({{w}}1{--}{{w}}2 [{vega}])+3.2). these results illustrate the power of large statistical studies of obscured quasars selected on the basis of mir and optical photometry. | composite spectral energy distributions and infrared-optical colors of type 1 and type 2 quasars |
supermassive primordial stars forming during catastrophic baryon collapse in atomically cooling halos at z ∼ 15-20 may be the origin of the first quasars in the universe. however, no simulation to date has followed the evolution of these halos at resolutions that are high enough or for times that are long enough to determine if collapse actually produces supermassive stars (smss). here we report new cosmological simulations of baryon collapse in atomically cooled halos for times that are long enough for smss to form and die as direct-collapse black holes (dcbhs). we find that the high infall rates required to build up such stars persist until the end of their lives and could fuel the rapid growth of their bhs thereafter. our simulations also demonstrate that binary and even small multiples of smss can form in low-spin and high-spin halos, respectively. this discovery raises the exciting possibility of detecting gravitational waves from dcbh mergers with lisa and tidal disruption events in the near-infrared with the james webb space telescope and ground-based telescopes in the coming decade. | the birth of binary direct-collapse black holes |
we report on the results of a new spectroscopic monitoring campaign of the quasar pg 0026+129 at the calar alto observatory 2.2 m telescope from 2017 july to 2020 february. significant variations in the fluxes of the continuum and broad emission lines, including hβ and he ii, were observed in the first and third years, and clear time lags between them are measured. the broad hβ line profile consists of two gaussian components: an intermediate-width h ${\beta }_{\mathrm{ic}}$ with an fwhm of 1964 ± 18 $\mathrm{km}\,{{\rm{s}}}^{-1}$ and another very broad h ${\beta }_{\mathrm{vbc}}$ with an fwhm of 7570 ± 83 $\mathrm{km}\,{{\rm{s}}}^{-1}$ . h ${\beta }_{\mathrm{ic}}$ has long time lags of ∼40-60 days in the rest frame, while h ${\beta }_{\mathrm{vbc}}$ shows nearly zero time delay with respect to the optical continuum at 5100 å. the velocity-resolved delays show consistent results: lags of ∼30-50 days at the core of the broad hβ line and roughly zero lags at the wings. h ${\beta }_{\mathrm{ic}}$ has a redshift of ∼400 $\mathrm{km}\,{{\rm{s}}}^{-1}$ , which seems to be stable for nearly 30 yr by comparing with archived spectra, and may originate from an infall. the rms spectrum of h ${\beta }_{\mathrm{vbc}}$ shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. both the double-peaked profile and the near-zero lag suggest that h ${\beta }_{\mathrm{vbc}}$ comes from a region associated with the part of the accretion disk that emits the optical continuum. adopting the fwhm (in the rms spectrum) and the time lag measured for the total hβ line, and a virial factor of 1.5, we obtain a virial mass of ${2.89}_{-0.69}^{+0.60}\times {10}^{7}\,{m}_{\odot }$ for the central black hole in this quasar. | evidence for two distinct broad-line regions from reverberation mapping of pg 0026+129 |
we look into the abundance of dual agn (active galactic nucleus) in the largest hydrodynamical simulation from the evolution and assembly of galaxies and their environment (eagle) project. we define a dual agn as two active black holes (bhs) with a separation below 30 kpc. we find that only 1 per cent of agn with lhx ≥ 1042 erg s-1 are part of a dual agn system at z = 0.8-1. during the evolution of a typical binary bh system, the rapid variability of the hard x-ray luminosity on myr time-scales severely limits the detectability of dual agn. to quantify this effect, we calculate a probability of detection, ton/t30, where t30 is the time in which the two bhs are separated at distances below 30 kpc and ton, the time that both agns are visible (e.g. when both agns have lhx ≥ 1042 erg s-1) in this period. we find that the average fraction of visible dual systems is 3 per cent. the visible dual agn distribution as a function of bh separation presents a pronounced peak at ∼20 kpc that can be understood as a result of the rapid orbital decay of the host galaxies after their first encounter. we also find that 75 per cent of the host galaxies have recently undergone or are undergoing a merger with stellar mass ratio ≥0.1. finally, we find that the fraction of visible dual agn increases with redshift as found in observations. | the abundances and properties of dual agn and their host galaxies in the eagle simulations |
context. in recent years, lyα nebulae have been routinely detected around high redshift, radio-quiet quasars thanks to the advent of the highly sensitive integral field spectrographs. constraining the physical properties of the lyα nebulae is crucial for a full understanding of the circum-galactic medium (cgm). the cgm acts both as a repository for intergalactic and galactic baryons as well as a venue of feeding and feedback processes. the most luminous quasars are privileged test-beds to study these processes, given their large ionising fluxes and dense cgm environments in which they are expected to be embedded.aims: we aim to characterise the rest-frame ultraviolet (uv) emission lines in the cgm around a hyper-luminous, broad emission line, radio-quiet quasar at z ∼ 3.6, which exhibits powerful outflows at both nuclear and host galaxy scales.methods: we analyse vlt/muse observations of the quasar j1538+08 (lbol = 6 × 1047 erg s-1), and we performed a search for extended uv emission lines to characterise its morphology, emissivity, kinematics, and metal content.results: we report the discovery of a very luminous (∼2 × 1044 erg s-1), giant lyα nebula and a likely associated extended (75 kpc) civ nebula. the lyα nebula emission exhibits moderate blueshift (∼440 km s-1) compared to the quasar systemic redshift and a large average velocity dispersion (σ¯v ∼ 700 km s-1) across the nebula, while the civ nebula shows average velocity dispersion of σ¯v ∼ 350 km s-1. the lyα line profile exhibits a significant asymmetry towards negative velocity values at 20-30 kpc south of the quasar and is well parametrised by the following two gaussian components: a narrow (σ ∼ 470 km s-1) systemic one plus a broad (σ ∼ 1200 km s-1), blueshifted (∼1500 km s-1) one.conclusions: our analysis of the muse observation of j1538+08 reveals metal-enriched cgm around this hyper-luminous quasar. furthermore, our detection of blueshifted emission in the emission profile of the lyα nebula suggests that powerful nuclear outflows can propagate through the cgm over tens of kiloparsecs. the reduced datacube is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/635/a157 based on data obtained with the european southern observatory very large telescope, paranal, chile, under programme 099.a-0316(a). | the wissh quasars project. viii. outflows and metals in the circum-galactic medium around the hyper-luminous z ∼ 3.6 quasar j1538+08 |
we use spectroscopy of close pairs of quasars to study diffuse gas in the circumgalactic medium (cgm) surrounding a sample of 40 damped lyα systems (dlas). the primary sightline in each quasar pair probes an intervening dla in the redshift range 1.6\lt {z}{dla}\lt 3.6, such that the second quasar sightline then probes lyα, c ii, si ii, and c iv absorption in the cgm transverse to the dla to projected distances {r}\perp \lt 300 kpc. analysis of the lyα profiles in these cgm sightlines constrains the covering fraction (fc) of optically thick h i (having column density nh i \gt {10}17.2 {{cm}}-2) to be ≳30% within {r}\perp \lt 200 kpc. strong si ii λ 1526 absorption with equivalent width {w}1526\gt 0.2 å occurs with an incidence {f}{{c}}({w}1526\gt 0.2 \mathringa )={20}-8+12% within {r}\perp \lt 100 kpc, indicating that si ii absorption associated with dlas probes material within a physical distance {r}3{{d}}≲ 30 kpc. however, we find that strong c iv λ1548 absorption is ubiquitous in these environments ({f}{{c}}({w}1548\gt 0.2 \mathringa )={57}-13+12% within {r}\perp \lt 100 kpc), and in addition exhibits a high degree of kinematic coherence on scales up to ∼175 kpc. we infer that this high-ionization material arises predominantly in large, quiescent structures extending beyond the scale of the dla host dark matter halos rather than in ongoing galactic winds. the lyα equivalent width in the dla-cgm is anticorrelated with {r}\perpat \gt 98% confidence, suggesting that dlas arise close to the centers of their host halos rather than on their outskirts. finally, the average lyα, and c ii and c iv equivalent widths measured as a function of {r}\perpare consistent with those measured around z ∼ 2 lyman break galaxies. assuming that dlas trace a galaxy population at lower masses and luminosities, this finding implies that the absorption strength of cool circumgalactic material has a weak dependence on dark matter halo mass at {m}{{h}}≲ {10}12 {m}⊙ . | dissecting the gaseous halos of z ∼ damped lyα systems with close quasar pairs |
the sloan digital sky survey has surveyed 14,555 square degrees of the sky, and delivered over a trillion pixels of imaging data. we present the large-scale clustering of 1.6 million quasars between z=0.5 and z=2.5 that have been classified from this imaging, representing the highest density of quasars ever studied for clustering measurements. this data set spans 0~ 11,00 square degrees and probes a volume of 80 h-3 gpc3. in principle, such a large volume and medium density of tracers should facilitate high-precision cosmological constraints. we measure the angular clustering of photometrically classified quasars using an optimal quadratic estimator in four redshift slices with an accuracy of ~ 25% over a bin width of δl ~ 10-15 on scales corresponding to matter-radiation equality and larger (0ℓ ~ 2-3). | sloan digital sky survey iii photometric quasar clustering: probing the initial conditions of the universe |
we investigate the structure of the mg ii broad line emission region in a sample of 284 type 1 active galactic nuclei (agns), through comparing the kinematical parameters of the broad mg ii and broad hβ lines. we found that the mg ii emitting region has more complex kinematics than the hβ one. it seems that the mg ii broad line originates from two subregions: one which contributes to the line core, which is probably virialized, and the other, `fountain-like' emitting region, with outflows-inflows nearly orthogonal to the disc, which become suppressed with stronger gravitational influence. this subregion mostly contributes to the emission of the mg ii broad line wings. the kinematics of the mg ii core emitting region is similar to that of the hβ broad line region (seems to be virialized), and therefore the full width at half-maximum (fwhm) of mg ii still can be used for the black hole (bh) mass estimation in the case where the mg ii core component is dominant. however, one should be careful with using the mg ii broad line for the bh mass estimation in the case of very large widths (fwhm > 6000 km s-1) and/or in the case of strong blue asymmetry. | the structure of the mg ii broad line emitting region in type 1 agns |
we perform two-dimensional radiation hydrodynamical simulations of accretion flows on to a black hole (bh) with a mass of 103 ≤ mbh/ m⊙ ≲ 106 in order to study rapid growth of bhs in the early universe. for spherically symmetric flows, hyper-eddington accretion from outside the bondi radius can occur unimpeded by radiation feedback when mbh ≳ 104 m⊙(n∞/105 cm - 3) - 1(t∞/104 k)3/2, where the density and temperature of ambient gas are initially set to n∞ = 105 cm-3 and t∞ = 104 k. here, we study accretion flows exposed to anisotropic radiation from a nuclear accretion disc with a luminosity higher than the eddington value (ledd) due to collimation towards the bipolar directions. we find that, unlike the spherically symmetric case, even less massive bhs with mbh < 104 m⊙ can be fed at high accretion rates of ≳ ledd/c2 through the equatorial region, while ionized regions expand towards the poles producing hot outflows with t ∼ 105 k. for more massive bhs with mbh ≳ 5 × 105 m⊙, intense inflows of neutral gas through the equator totally cover the central radiating region due to the non-radial gas motions. because of efficient recombination by hydrogen, the entire flow settles in neutral and warm gas with t ≃ 8000 k. the bh is fed at a rate of ∼5 × 104ledd/c2 (a half of the inflow rate from the bondi radius). moreover, radiation momentum absorbed by neutral hydrogen produces warm outflows towards the bipolar directions at ∼ 10 per cent of the bh feeding rate and with a velocity several times higher than the escaping value. | rapid growth of black holes accompanied with hot or warm outflows exposed to anisotropic super-eddington radiation |
we compare the measured angular cross-correlation between the fermi-large area telescope γ-ray sky and catalogs of extragalactic objects with the expected signal induced by weakly interacting massive particle (wimp) dark matter (dm). we include a detailed description of the contribution of astrophysical γ-ray emitters such as blazars, misaligned active galactic nucleus (agn), and star-forming galaxies, and perform a global fit to the measured cross-correlation. five catalogs are considered: sloan digital sky survey (sdss)-dr6 quasars, two micron all sky survey galaxies, nrao vla sky survey radio galaxies, sdss-dr8 luminous red galaxies, and the sdss-dr8 main galaxy sample. to model the cross-correlation signal, we use the halo occupation distribution formalism to estimate the number of galaxies of a given catalog in dm halos and their spatial correlation properties. we discuss uncertainties in the predicted cross-correlation signal arising from the dm clustering and wimp microscopic properties, which set the dm γ-ray emission. the use of different catalogs probing objects at different redshifts significantly reduces, though not completely, the degeneracy among the different γ-ray components. we find that the presence of a significant wimp dm signal is allowed by the data but not significantly preferred by the fit, although this is mainly due to a degeneracy with the misaligned agn component. with modest substructure boost, the sensitivity of this method excludes thermal annihilation cross sections at 95% level for wimp masses up to few tens of gev. constraining the low-redshift properties of astrophysical populations with future data will further improve the sensitivity to dm. | dark matter searches in the gamma-ray extragalactic background via cross-correlations with galaxy catalogs |
we use a sample of 1669 quasars (r < 20.15, 3.6 < z < 4.0) from the baryon oscillation spectroscopic survey to study the intrinsic shape of their continuum and the lyman continuum photon escape fraction (fesc,q), estimated as the ratio between the observed flux and the expected intrinsic flux (corrected for the intergalactic medium absorption) in the wavelength range 865-885 å rest frame. modelling the intrinsic quasar (qso) continuum shape with a power law, fλ ∝ λ-γ, we find a median γ = 1.30 (with a dispersion of 0.38, no dependence on the redshift and a mild intrinsic luminosity dependence) and a mean fesc,q = 0.75 (independent of the qso luminosity and/or redshift). the fesc,q distribution shows a peak around zero and a long tail of higher values, with a resulting dispersion of 0.7. if we assume for the qso continuum a double power-law shape (also compatible with the data) with a break located at λbr = 1000 å and a softening δγ = 0.72 at wavelengths shorter than λbr, the mean fesc,q rises to 0.82. combining our γ and fesc,q estimates with the observed evolution of the active galactic nucleus (agn) luminosity function (lf), we compute the agn contribution to the uv ionizing background (uvb) as a function of redshift. agn brighter than one-tenth of the characteristic luminosity of the lf are able to produce most of it up to z ∼ 3, if the present sample is representative of their properties. at higher redshifts, a contribution of the galaxy population is required. assuming an escape fraction of lyman continuum photons from galaxies between 5.5 and 7.6 per cent, independent of the galaxy luminosity and/or redshift, a remarkably good fit to the observational uvb data up to z ∼ 6 is obtained. at lower redshift, the extrapolation of our empirical estimate agrees well with recent uvb observations, dispelling the so-called photon underproduction crisis. | the spectral slope and escape fraction of bright quasars at z ∼ 3.8: the contribution to the cosmic uv background |
feedback from active galactic nuclei (agn) is widely considered to be the main driver in regulating the growth of massive galaxies through heating or driving gas out of the galaxy, preventing further increase in stellar mass. observational proof for this scenario has, however, been scarce. we have assembled a sample of 132 radio-quiet type-2 and red agn at 0.1 < z < 1. we measure the kinematics of the agn-ionized gas, the host galaxies' stellar masses and star formation rates (sfrs) and investigate the relationships between agn luminosities, specific star formation rates (ssfrs) and outflow strengths w90 - the 90 per cent velocity width of the [o iii]λ5007å line power and a proxy for the agn-driven outflow speed. outflow strength is independent of ssfr for agn selected on their mid-ir luminosity, in agreement with previous work demonstrating that star formation is not sufficient to produce the observed ionized gas outflows which have to be powered by agn activity. more importantly, we find a negative correlation between w90 and ssfr in the agn hosts with the highest sfrs, i.e. with the highest gas content, where presumably the coupling of the agn-driven wind to the gas is strongest. this implies that agn with strong outflow signatures are hosted in galaxies that are more `quenched' than galaxies with weaker outflow signatures. despite the galaxies' high sfrs, we demonstrate that the outflows are not star formation driven but indeed due to agn powering. this observation is consistent with the agn having a net suppression, `negative' impact, through feedback on the galaxies' star formation history. | evidence of suppression of star formation by quasar-driven winds in gas-rich host galaxies at z < 1? |
we report the detection of extended hα emission from the tip of the h i disc of the nearby edge-on galaxy ugc 7321, observed with the multi unit spectroscopic explorer (muse) instrument at the very large telescope. the hα surface brightness fades rapidly where the h i column density drops below n_{h i}∼ 10^{19} cm-2, consistent with fluorescence arising at the ionization front from gas that is photoionized by the extragalactic ultraviolet background (uvb). the surface brightness measured at this location is (1.2 ± 0.5) × 10-19 erg s- 1 cm- 2 arcsec- 2, where the error is mostly systematic and results from the proximity of the signal to the edge of the muse field of view, and from the presence of a sky line next to the redshifted hα wavelength. by combining the hα and the h i 21 cm maps with a radiative transfer calculation of an exponential disc illuminated by the uvb, we derive a value for the h i photoionization rate of γ _{h i} ∼ (6-8)× 10^{-14} s^{-1}. this value is consistent with transmission statistics of the lyα forest and with recent models of a uvb that is dominated by quasars. | a measurement of the z = 0 uv background from hα fluorescence |
we present kiloparsec-scale atacama large millimeter/submillimeter array (alma) and hubble space telescope imaging of the quasar pj308-21 at z = 6.2342, tracing dust, gas (via the [c ii] 158 μm line), and young stars. at a resolution of ∼0.″3 (≈1.7 kpc), the system is resolved over >4″ (>20 kpc). in particular, it features a main component, identified to be the quasar host galaxy, centered on the accreting supermassive black hole; and two other extended components are on the west and east side: one redshifted and the other blueshifted relative to the quasar. the [c ii] emission of the entire system stretches over >1500 km s-1 along the line of sight. all the components of the system are observed in dust, [c ii], and rest-frame ultraviolet (uv) emission. the inferred [c ii] luminosities [(0.9-4.6)×109 {l}⊙ ]; dust luminosities [(0.15-2.6)×1012 {l}⊙ ]; rest-frame uv luminosities [(6.6-15)×1010 {l}⊙ ], their ratios, and the implied gas/dust masses; and star formation rates [11-290 {m}⊙yr-1] are typical of high-redshift star-forming galaxies. a toy model of a single satellite galaxy that is tidally stripped by the interaction with the quasar host galaxy can account for the observed velocity and spatial extent of the two extended components. an outflow interpretation of the unique features in pj308-21 is not supported by the data. pj308-21 is thus one of the earliest galaxy mergers imaged at cosmic dawn. | alma and hst kiloparsec-scale imaging of a quasar-galaxy merger at z ≈ 6.2 |
we present alma 0.″28 × 0.″20 (1.4 kpc × 1.0 kpc) resolution observations of the [c ii] 158 μm line and underlying dust continuum in the host galaxy of the most distant quasar currently known, ulas j1342+0928 at z = 7.5413. both the [c ii] and continuum are detected and spatially resolved. the [c ii] line is ∼1.5 times more extended than the continuum emission, showing an elongated and complex structure of approximately 3.2 kpc × 6.4 kpc. two separate peaks are clearly seen (≳6σ each) in three 100 km s-1 width [c ii] channel maps. the velocity field of the [c ii] gas does not show evidence of a coherent rotation field but rather chaotic motion reminiscent of an ongoing merger. | the z = 7.54 quasar ulas j1342+0928 is hosted by a galaxy merger |
blazars are a subpopulation of quasars whose jets are nearly aligned with the line of sight, which tend to exhibit multiwavelength variability on a variety of time-scales. quasi-periodic variability on year-like time-scales has been detected in a number of bright sources, and has been connected to the orbital motion of a putative massive black hole binary. if this were indeed the case, those blazar binaries would contribute to the nanohertz gravitational-wave stochastic background. we test the binary hypothesis for the blazar population observed by the fermi gamma-ray space telescope, which consists of bl lacertae objects and flat-spectrum radio quasars. using mock populations informed by the luminosity functions for bl lacertae objects and flat-spectrum radio quasars with redshifts z ≤ 2, we calculate the expected gravitational-wave background and compare it to recent pulsar timing array upper limits. the two are consistent only if a fraction ≲10-3 of blazars hosts a binary with orbital periods <5 yr. we therefore conclude that binarity cannot significantly explain year-like quasi-periodicity in blazars. | pulsar timing constraints on the fermi massive black hole binary blazar population |
we investigate a scenario where primordial black holes (pbhs) can be the progenitors of supermassive black holes (smbhs) observed at z ∼6 . to this end, we carried out clustering analysis using a sample of 81 quasars at 5.88 <z <6.49 , which is constructed in the subaru high-z exploration of low-luminosity quasars project, and 11 quasars in the same redshift range selected from the literature. the resulting angular autocorrelation function (acf) can be fitted to a power law form of ωθ=0.04 5-0.106+0.114θ-0.8 over a scale of 0.2-10 degrees. we compare the acf of the quasars to that predicted for the pbh model at z ∼6 and found that such a scenario is excluded for a broad range of parameter space, from which we can conclude that a scenario with pbhs as smbhs is not viable. we also discuss a model in which smbhs at z ∼6 originate from the direct collapse of pbh clumps and argue that the observed acf excludes such a scenario in the context of our pbh model. | supermassive primordial black holes: a view from clustering of quasars at z ∼6 |
in this paper, we study the sizes of quasar proximity zones with synthetic quasar absorption spectra obtained by postprocessing a cosmic reionization on computers (croc) simulation. croc simulations have both relatively large box sizes and high spatial resolution, allowing us to resolve lyman limit systems (llss), which are crucial for modeling the quasar absorption spectra. we find that before reionization, most quasar proximity zone sizes grow steadily for ∼10 myr, while after reionization, they grow rapidly but only for ∼0.1 myr. we also find a slow growth of robs with decreasing turn-on redshift. in addition, we find that ∼1%-2% of old quasars (30 myr old) display extremely small proximity zone sizes (<1 proper mpc), the vast majority of which are due to the occurrence of a damped lyα absorber (dla) or an lls along the line of sight. these dlas and llss are contaminated with metal, which offers a way to distinguish them from the normal proximity zones of young quasars. | the distribution and evolution of quasar proximity zone sizes |
supermassive black holes (smbhs) are found in most galactic nuclei. a significant fraction of these nuclei also contains a nuclear stellar cluster (nsc) surrounding the smbh. in this paper, we consider the idea that the nsc forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (imbhs). these imbhs can subsequently grow in the nsc and form an smbh. we carry out n-body simulations of the simultaneous merger of three stellar clusters to form an nsc, and investigate the outcome of simulated runs containing zero, one, two, and three imbhs. we find that imbhs can efficiently sink to the centre of the merged cluster. if multiple merging clusters contain an imbh, we find that an imbh binary is likely to form and subsequently merge by gravitational wave emission. we show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. the seed smbh will be ejected from the nsc by the recoil kick produced when two imbhs merge, if their mass ratio q ≳ 0.15. if the seed is ejected then no smbh will form in the nsc. this is a natural pathway to explain those galactic nuclei that contain an nsc but apparently lack an smbh, such as m33. however, if an imbh is retained then it can seed the growth of an smbh through gas accretion and tidal disruption of stars. | formation of supermassive black holes in galactic nuclei - i. delivering seed intermediate-mass black holes in massive stellar clusters |
we report spatially resolved dust properties of the quasar host galaxy bri1335-0417 at redshift z = 4.4 constrained by the atacama large millimetre/submillimetre array observations. the dust temperature map, derived from a greybody fit to rest frame 90 and 161 μm continuum images, shows a steep increase towards the centre, reaching 57.1 ± 0.3 k and a flat median profile at the outer regions of ~38 k. image decomposition analysis reveals the presence of a point source in both dust continuum images spatially coincident with the highest temperature peak and the optical quasar position, which we attribute to warm dust heated by an active galactic nucleus (agn). we show that a model including this warm component along with cooler dust heated by star formation describes the global spectral energy distribution better than a single-component model, with dust temperatures of 87.1$^{+34.1}_{-18.3}$ k (warm component) and 52.6$^{+10.3}_{-11.0}$ k (cold component). the star-formation rate (sfr) estimated from the cold dust component is $1700_{-400}^{+500}\ \mathrm{m}_\odot$ yr-1, a factor of three smaller than previous estimates due to a large agn contribution ($53^{+14}_{-15}$ per cent). the unresolved warm dust component also explains the steep temperature gradient, as the temperature profile derived after the point source subtraction is flat. the point source subtraction also reduces the estimated central sfr surface density σsfr by over a factor of three. with this correction, spatially resolved measurements of σsfr and the surface gas mass density σgas form a roughly linear sequence in the kennicutt-schmidt diagram with a constant gas depletion time of 50-200 myr. the demonstrated agn-host galaxy decomposition reveals the importance of spatially resolved data for accurate measurements of quasar host galaxy properties, including dust temperature, sfrs, and size. | spatially resolved dust properties and quasar-galaxy decomposition of a hyper-luminous infrared galaxy at z = 4.4 |
we present spatially resolved h α properties of 21 type 1 agn host galaxies at z ~ 2 derived from the super survey. these targets were observed with the adaptive optics capabilities of the sinfoni spectrograph, a near-infrared integral field spectrograph, that provided a median spatial resolution of 0.3 arcsec (~2 kpc). we model the h α emission line profile in each pixel to investigate whether it traces gas in the narrow line region or if it is associated with star formation. to do this, we first investigate the presence of resolved h α emission after subtracting the agn psf. we find extended h α emission in 16 out of the 21 type 1 agn host galaxies (76 per cent). based on the bpt diagnostics, optical line flux ratios and line widths (fwhm), we show that the h α emission in five galaxies is ionized by the agn (30 per cent), in four galaxies by star formation (25 per cent) and for the rest (45 per cent), the ionization source is unconstrained. two galaxies show extended h α fwhm >600 km s-1, which is interpreted as a part of an agn-driven outflow. morphological and kinematic maps of h α emission in targets with sufficient signal-to-noise ratio suggest the presence of rotationally supported discs in six galaxies and possible presence of companions in four galaxies. in two galaxies, we find an anticorrelation between the locations of extended h α emission and [o iii]-based ionized outflows, indicating possible negative feedback at play. however, in the majority of galaxies, we do not find evidence of outflows impacting h α-based star formation. | super vii. morphology and kinematics of h α emission in agn host galaxies at cosmic noon using sinfoni |
we present an analytic model for the cool, t ~ 104 k, circumgalactic medium (cgm), describing the gas distribution, and thermal and ionization states. our model assumes (total) pressure equilibrium with the ambient warm/hot cgm, photoionization by the metagalactic radiation, and allows for nonthermal pressure support, parameterized by the ratio of thermal pressures, η = p hot,th/p cool,th. we apply the model to the cos-halos measurements and find that a nominal model with η = 3, gas distribution out to r ≈ 0.6r vir, and m cool = 3 × 109 m ⊙, corresponding to a volume filling fraction of f v,cool ≈ 1%, reproduces the h i and low/intermediate metal ions (c ii, c iii, si ii, si iii, and mg ii) mean column densities. variation of ±0.5 dex in η or m cool encompasses ~2/3 of the scatter between objects. our nominal model underproduces the measured c iv and si iv columns, and these can be reproduced with (i) a cool phase with m cool ~ 1010 m ⊙ and η ≈ 5, or (ii) cooling or mixing gas at intermediate temperatures, with m ~ 1.5 × 1010 m ⊙ and occupying ~1/2 of the total cgm volume. for cool gas with f v,cool ≈ 1%, we estimate an upper limit on the cloud sizes, r cl ≲ 0.5 kpc. our results suggest that for the average galaxy cgm, the mass and nonthermal support in the cool phase are lower than previously estimated, and extreme scenarios are not necessary. we estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be offset, allowing ${\dot{m}}_{\mathrm{cool}}\approx 0$ over long timescales. | the cool circumgalactic medium of low-redshift star-forming galaxies. i. empirical model and mean properties |
reservoirs of dense atomic gas (primarily hydrogen) contain approximately 90 per cent of the neutral gas at a redshift of 3, and contribute to between 2 and 3 per cent of the total baryons in the universe1-4. these `damped lyman α systems'—so called because they absorb lyman α photons within and from background sources—have been studied for decades, but only through absorption lines present in the spectra of background quasars and γ-ray bursts5-10. such pencil beams do not constrain the physical extent of the systems. here we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped lyman α systems. these systems are greater than 238 kiloparsecs squared in extent, with column densities of neutral hydrogen varying by more than an order of magnitude on scales of less than 3 kiloparsecs. the mean column densities are between 1020.46 and 1020.84 centimetres squared and the total masses are greater than 5.5 × 108-1.4 × 109 times the mass of the sun, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts greater than 2. | resolving the h i in damped lyman α systems that power star formation |
the chandra deep fields (cdfs), being a major thrust among extragalactic x-ray surveys and complemented effectively by multiwavelength observations, have critically contributed to our dramatically improved characterization of the 0.5-8 kev cosmic x-ray background sources, the vast majority of which are distant active galactic nuclei (agns) and starburst and normal galaxies. in this review, i highlight some recent key observational results, mostly from the cdfs, on the agn demography, the interactions between agns and their host galaxies, the evolution of non-active galaxy x-ray emission, and the census of x-ray galaxy groups and clusters through cosmic time, after providing the necessary background information. i then conclude by summarizing some significant open questions and discussing future prospects for moving forward. | the chandra deep fields: lifting the veil on distant active galactic nuclei and x-ray emitting galaxies |
context. to fully exploit the scientific potential of the fermi mission for the physics of active galactic nuclei (agn), we initiated the f-gamma programme. between 2007 and 2015 the f-gamma was the prime provider of complementary multi-frequency monitoring in the radio regime.aims: we quantify the radio variability of γ-ray blazars. we investigate its dependence on source class and examine whether the radio variability is related to the γ-ray loudness. finally, we assess the validity of a putative correlation between the two bands.methods: the f-gamma performed monthly monitoring of a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39 ghz. we perform a time series analysis on the first 2.5-yr data set to obtain variability parameters. a maximum likelihood analysis is used to assess the significance of a correlation between radio and γ-ray fluxes.results: we present light curves and spectra (coherent within ten days) obtained with the effelsberg 100 m and iram 30 m telescopes. all sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60-80 ghz as expected by shock-in-jet models. compared to flat-spectrum radio quasars (fsrqs), bl lacertae objects (bl lacs) show systematically lower variability amplitudes, brightness temperatures, and doppler factors at lower frequencies, while the difference vanishes towards higher ones. the time scales appear similar for the two classes. the distribution of spectral indices appears flatter or more inverted at higher frequencies for bl lacs. evolving synchrotron self-absorbed components can naturally account for the observed spectral variability. we find that the fermi-detected sources show larger variability amplitudes, brightness temperatures, and doppler factors than non-detected ones. flux densities at 86.2 and 142.3 ghz correlate with 1 gev fluxes at a significance level better than 3σ, implying that γ rays are produced very close to the mm-band emission region. tables of the measured fluxes are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/596/a45 | the f-gamma programme: multi-frequency study of active galactic nuclei in the fermi era. programme description and the first 2.5 years of monitoring |
bright active galaxies show a range of properties, but many of these properties are correlated, which has led to the concept of the quasar main sequence. we test whether our current understanding of the quasar structure allows the pattern observed in the optical plane formed by the kinematic line width of hβ and the relative importance of the fe ii optical emission to be reproduced. we performed simulations of the hβ and fe ii production using the code cloudy and well-justified assumptions about the broadband spectra, distance to the emission line region, and the cloud properties. we show that the presence of the warm corona is an important element of the broadband spectrum, which decreases the dependence of the relative fe ii emissivity on the eddington ratio and allows the rare cases of particularly strong fe ii emitters to be reproduced. results are sensitive to the adopted cloud distance, and strong fe ii emission can be obtained either by adopting strongly supersolar metallicity or a much shorter distance than traditionally obtained from reverberation mapping. we modeled in a similar way the uv plane defined by the mg ii line and fe ii uv pseudo-continuum, but here our approach is less successful, in general overproducing the fe ii strength. we found that the fe ii optical and uv emissivity depend in a different way on the turbulent velocity and metallicity, and the best extension of the model in order to cover both planes is to allow very large turbulent velocities in the broad-line region clouds. | cloudy view of the warm corona |
we present a qualitative analysis of the variability of quasar broad absorption lines using the large multi-epoch spectroscopic data set of the sloan digital sky survey data release 10. we confirm that variations of absorption lines are highly coordinated among different components of the same ion or the same absorption component of different ions for c iv, si iv, and n v. furthermore, we show that the equivalent widths (ews) of the lines decrease or increase statistically when the continuum brightens or dims. this is further supported by the synchronized variations of emission and absorption-line ews when the well-established intrinsic baldwin effect for emission lines is taken into account. we find that the emergence of an absorption component is usually accompanied by the dimming of the continuum while the disappearance of an absorption-line component is accompanied by the brightening of the continuum. this suggests that the emergence or disappearance of a c iv absorption component is only the extreme case, when the ionic column density is very sensitive to continuum variations or the continuum variability the amplitude is larger. these results support the idea that absorption-line variability is driven mainly by changes in the gas ionization in response to continuum variations, that the line-absorbing gas is highly ionized, and in some extreme cases, too highly ionized to be detected in uv absorption lines. due to uncertainties in the spectroscopic flux calibration, we cannot quantify the fraction of quasars with asynchronized continuum and absorption-line variations. | evidence for photoionization-driven broad absorption line variability |
blazars are highly variable active galactic nuclei that emit radiation at all wavelengths from radio to gamma rays. polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies, and it also varies dramatically. the polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. however, even though numerous measurements have been performed, the mechanisms behind jet creation, composition, and variability are still debated. we performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between 2008 july and 2014 december to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. we identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in parsec-scale relativistic jets between different types of blazars (flat-spectrum radio quasars vs. bl lacs) and consequently between different types of radio galaxies (fr i versus fr ii). | systematic study of gamma-ray-bright blazars with optical polarization and gamma-ray variability |
coalescence of intermediate-mass black holes (imbhs) as a result of the migration toward galactic centres via dynamical friction may contribute to the formation of supermassive bhs. here we reinvestigate the gaseous dynamical friction, which was claimed to be inefficient with radiative feedback from bhs in literature, by performing 3d radiation-hydrodynamics simulations that solve the flow structure in the vicinity of bhs. we consider a 104-m⊙ bh moving at the velocity vflow through the homogeneous medium with metallicity z in the range of 0-0.1 z⊙ and density n∞. we show that, if n∞ ≲ 106 cm-3 and vflow ≲ 60 km s-1, the bh is accelerated forward because of the gravitational pull from a dense shell ahead of an ionized bubble around the bh, regardless of the value of z. if n∞ ≳ 106 cm-3, however, our simulation shows the opposite result. the ionized bubble and associating shell temporarily appear, but immediately go downstream with significant ram pressure of the flow. they eventually converge into a massive downstream wake, which gravitationally drags the bh backward. the bh decelerates over the time-scale of ∼0.01 myr, much shorter than the dynamical time-scale in galactic discs. our results suggest that imbhs that encounter the dense clouds rapidly migrate toward galactic centres, where they possibly coalescence with others. | gaseous dynamical friction under radiative feedback: do intermediate-mass black holes speed up or down? |
very long baseline interferometry (vlbi) at millimeter (mm) wavelengths is being employed to resolve event horizon-scale structure of the environment surrounding the milky way black hole at an angular resolution of a few tens of microarcseconds. the same approach could also resolve the orbital separation of a population of massive black hole binaries (mbhbs). modeling the inspiral of binaries due to gravitational-wave emission and gas and requiring binary orbital periods of less than 10 yr, we estimate that there may exist ∼100 resolvable mbhbs that are bright enough to be observed by mm-wavelength vlbi instruments over the entire sky at redshifts z ≲ 0.5. we propose to search for these resolvable mbhbs by identifying binaries with the required orbital separations from periodic quasar light curves identified in optical and near-ir surveys. these periodic-light-curve candidates can be followed up with radio observations to determine their promise for observation with vlbi at mm wavelengths. the vlbi observations over the timescale of a binary orbit can allow unprecedented precision in the measurement of the binary mass, to within 30%. in combination with an independent binary mass measurement, vlbi observation would allow a novel { \mathcal o }(10 % ) measurement of the hubble constant, independent from those currently proposed and employed. | repeated imaging of massive black hole binary orbits with millimeter interferometry: measuring black hole masses and the hubble constant |
in this paper, the generalized equation of state (geos) for dark energy (w_β =w_0-w_{β }[(1+z)^{-β }-1]/β ) is investigated with the combined standard ruler data from the observations of intermediate-luminosity radio quasars, galaxy clusters, bao and cmb. the constraint results show that the best-fit eos parameters are w_0=- 0.94^{+0.57}_{-0.41}, w_β =- 0.17^{+2.45}_{-4.81} and β =-1.42 (with a lower limit of β >- 2.70 at 68.3% c.l.), which implies that at early times the dark energy vanishes. in the framework of nine truncated geos models with different β parameters, our findings present very clear evidence disfavoring the case that dark energy always dominates over the other material components in the early universe. moreover, stringent constraints can be obtained in combination with the latest measurements of hubble parameter at different redshifts: w_0=-1.01^{+0.56}_{-0.31}, w_β =0.01^{+2.33}_{-4.52} and β =-0.42 (with a lower limit of β >-2.40 at 68.3% c.l.). finally, the results obtained from the transition redshift (z_t) and om( z) diagnostic indicate that: (1) the above constraints on the geos model agree very well with the transition redshift interval 0.49 ≤ z_t ≤ 0.88 within 1σ error region. (2) at the current observational level, the geos model is practically indistinguishable from λ cdm, although a small deviation from λ cdm cosmology is present in the combined standard ruler data. | the generalized cosmic equation of state: a revised study with cosmological standard rulers |
(abridged) the scale of the acoustic oscillation of baryons at the baryon-photon decoupling is imprinted on the spatial distribution of galaxies in the universe, known as the baryon acoustic oscillation (bao). the correlation functions and power spectrum are used as a central tool for the studies on the bao analysis. in this work, we analyzed the spatial distribution of galaxies with a method from the topological data analysis (tda), in order to detect and examine the bao signal in the galaxy distribution. the tda provides a method to treat various types of "holes" in point set data, by constructing the persistent homology (ph) group from the geometric structure of data points and handling the topological information of the dataset. we can obtain the information on the size, position, and statistical significance of the holes in the data. a particularly strong point of the persistent homology is that it can classify the holes by their spatial dimension, i.e., a 0-dim separation, 1-dim loop, 2-dim shell, etc. we first analyzed the simulation datasets with and without the baryon physics to examine the performance of the ph method. we found that the ph is indeed able to detect the bao signal: simulation data with baryon physics present a prominent signal from the bao, while data without baryon physics does not show this signal. then, we applied the ph to a quasar sample at $z <1.0$ from extended baryon oscillation spectroscopic survey in sloan digital sky survey data release 14. we discovered a characteristic hole (a hollow shell) at a scaler $\sim150\ [{\rm mpc}]$. this exactly corresponds to the bao signature imprinted in the galaxy/quasar distribution. we performed this analysis on a small subsample of 2000 quasars. this clearly demonstrates that the ph analysis is very efficient in finding this type of topological structures even if the sampling is very sparse. | a study on the baryon acoustic oscillation with topological data analysis |
aims: we present new data for four candidate obscured compton-thick (ct) quasars at z ~ 1-2.5 observed with the sinfoni vlt spectrograph in adaptive optics (ao) mode. these sources were selected from a 24 μm spitzer mips survey of the cosmos field, on the basis of red mid-infrared to optical and optical to near-infrared colours, with the intention of identifying active galactic nuclei (agns) in dust enshrouded environments, where most of the black hole mass is assembled.methods: near-infrared spectra were analysed to check for emission line features and to search for broad components in the [oiii]-hβ and hα-[nii] regions. we also employed x-ray spectral analysis, radio and mir diagnostics, and sed fitting to study the nature of the sources.results: we successfully identified three objects for which we had only a photometric redshift estimate. based on their emission line diagnostics and on ancillary multi-wavelength constraints, we find that all four targets harbour obscured agns. broad profiles, which could be attributed to the effects of outflows, are revealed in only one target, miro20581. in particular, we clearly resolved a fast (~1600 km s-1) and extended (~5 kpc) outflow in the [oiii]5007 emission line. this feature, the commonly used indicator for ionised outflowing gas, was only sampled and detected for this target; hence, we cannot exclude the presence of outflows in the other sources. overall, the constraints we obtain from our targets and from other comparative samples from the literature suggest that these optically faint luminous infrared galaxies, hosting obscured agns, may represent a brief evolutionary phase between the post-merger starburst and the unobscured quasar phases. based on observations with sinfoni vlt spectrograph, eso program 092.a-0884(a). | sinfoni spectra of heavily obscured agns in cosmos: evidence of outflows in a mir/o target at z ~ 2.5 |
we study the correlation of galaxy structural properties with their location relative to the sfr-m* correlation, also known as the star formation `star-forming main sequence' (sfms), in the cosmic assembly near-infrared deep extragalactic legacy survey and galaxy and mass assembly survey and in a semi-analytic model (sam) of galaxy formation. we first study the distribution of median sérsic index, effective radius, star formation rate (sfr) density and stellar mass density in the sfr-m* plane. we then define a redshift-dependent main sequence and examine the medians of these quantities as a function of distance from this main sequence, both above (higher sfrs) and below (lower sfrs). finally, we examine the distributions of distance from the main sequence in bins of these quantities. we find strong correlations between all of these galaxy structural properties and the distance from the sfms, such that as we move from galaxies above the sfms to those below it, we see a nearly monotonic trend towards higher median sérsic index, smaller radius, lower sfr density, and higher stellar density. in the sam, bulge growth is driven by mergers and disc instabilities, and is accompanied by the growth of a supermassive black hole which can regulate or quench star formation via active galactic nucleus feedback. we find that our model qualitatively reproduces the trends described above, supporting a picture in which black holes and bulges co-evolve, and active galactic nucleus feedback plays a critical role in moving galaxies off of the sfms. | the relationship between star formation activity and galaxy structural properties in candels and a semi-analytic model |
we present single-epoch black hole mass ({m}bh}) calibrations based on the rest-frame ultraviolet (uv) and optical measurements of mg ii 2798 å and hβ 4861 å lines and the active galactic nucleus (agn) continuum, using a sample of 52 moderate-luminosity agns at z ∼ 0.4 and z ∼ 0.6 with high-quality keck spectra. we combine this sample with a large number of luminous agns from the sloan digital sky survey to increase the dynamic range for a better comparison of uv and optical velocity and luminosity measurements. with respect to the reference {m}bh} based on the line dispersion of hβ and continuum luminosity at 5100 å, we calibrate the uv and optical mass estimators by determining the best-fit values of the coefficients in the mass equation. by investigating whether the uv estimators show a systematic trend with eddington ratio, fwhm of hβ, fe ii strength, or uv/optical slope, we find no significant bias except for the slope. by fitting the systematic difference of mg ii-based and hβ-based masses with the l 3000/l 5100 ratio, we provide a correction term as a function of the spectral index as δc = 0.24 (1 + αλ ) + 0.17, which can be added to the mg ii-based mass estimators if the spectral slope can be well determined. the derived uv mass estimators typically show >∼0.2 dex intrinsic scatter with respect to the hβ-based {m}bh}, suggesting that the uv-based mass has an additional uncertainty of ∼0.2 dex, even if high-quality rest-frame uv spectra are available. | calibration and limitations of the mg ii line-based black hole masses |
we report on the veritas detection of very-high-energy (vhe, $e > 100~\mathrm{gev}$) $\gamma$-ray emission from the optically bright quasar oj 287 which is located at a redshift of z = 0.306. oj 287 has been observed to display regular optical outbursts with a period of approximately 12 years, with the last major optical outburst having occurred in 2015. to explain this periodicity, models involving a binary supermassive black hole system at the core of oj 287, or a helical jet, have been developed. motivated by elevated swift-xrt count rates, veritas observed oj 287 in february 2017, and detected the object at >5 standard deviations above background. this detection prompted further veritas, swift-xrt and multiwavelength observations of the object. the results of the veritas observational campaign are presented. | veritas detection of vhe emission from the optically bright quasar oj 287 |
the quasar 3c 454.3 is a blazar known for its rapid and violent outbursts seen across the electromagnetic spectrum. using γ-ray, x-ray, multiband optical, and very-long-baseline interferometric data we investigate the nature of two such events that occurred in 2013 and 2014 accompanied by strong variations in optical polarization, including a ∼230° electric vector position angle (evpa) rotation. our results suggest that a single disturbance was responsible for both flaring events. we interpret the disturbance as a shock propagating down the jet. under this interpretation the 2013 flare originated most likely due to changes in the viewing angle caused by perhaps a bent or helical trajectory of the shock upstream of the radio core. the 2014 flare and optical polarization behavior are the result of the shock exiting the 43 ghz radio core, suggesting that shock crossings are one of the possible mechanisms for evpa rotations. | two flares with one shock: the interesting case of 3c 454.3 |
cosmic gas cycles in and out of galaxies, but outside of galaxies it is difficult to observe except for the absorption lines that circumgalactic clouds leave in the spectra of background quasars. using photoionization modeling of those lines to determine cloud pressures, we find that galaxies are surrounded by extended atmospheres that confine the clouds and have a radial pressure profile that depends on galaxy mass. motivated by observations of the universe’s most massive galaxies, we compare those pressure measurements with models predicting the critical pressure at which cooler clouds start to precipitate out of the hot atmosphere and rain toward the center. we find excellent agreement, implying that the precipitation limit applies to galaxies over a wide mass range. | circumgalactic pressure profiles indicate precipitation-limited atmospheres for {m}_{* }\\sim {10}^{9}{--}{10}^{11.5}\\,{m}_{\\odot } |
the fermi-large area telescope (lat) is currently the most important facility for investigating the gev γ-ray sky. with fermi-lat, more than three thousand γ-ray sources have been discovered so far. 1144 (∼40 per cent) of the sources are active galaxies of the blazar class, and 573 (∼20 per cent) are listed as blazar candidate of uncertain type (bcu), or sources without a conclusive classification. we use the empirical cumulative distribution functions and the artificial neural networks for a fast method of screening and classification for bcus based on data collected at γ-ray energies only, when rigorous multiwavelength analysis is not available. based on our method, we classify 342 bcus as bl lacs and 154 as flat-spectrum radio quasars, while 77 objects remain uncertain. moreover, radio analysis and direct observations in ground-based optical observatories are used as counterparts to the statistical classifications to validate the method. this approach is of interest because of the increasing number of unclassified sources in fermi catalogues and because blazars and in particular their subclass high synchrotron peak objects are the main targets of atmospheric cherenkov telescopes. | blazar flaring patterns (b-flap) classifying blazar candidate of uncertain type in the third fermi-lat catalogue by artificial neural networks |
we investigate the relation between star formation rates (dot{{m}}_s) and agn properties in optically selected type 1 quasars at 2 < z < 3 using data from herschel and the sdss. we find that dot{{m}}_s remains approximately constant with redshift, at 300 ± 100 m⊙ yr-1. conversely, dot{{m}}_s increases with agn luminosity, up to a maximum of ∼ 600 m⊙ yr-1, and with c iv fwhm. in context with previous results, this is consistent with a relation between dot{{m}}_s and black hole accretion rate (dot{{m}}_{bh}) existing in only parts of the z-dot{{m}}s-dot{{m}}_{bh} plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. the relations between dot{{m}}_s and both agn luminosity and c iv fwhm are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. star formation rates are observed to decline with increasing c iv equivalent width. this decline can be partially explained via the baldwin effect, but may have an additional contribution from one or more of three factors; mi is not a linear tracer of l2500, the baldwin effect changes form at high agn luminosities, and high c iv ew values signpost a change in the relation between dot{{m}}_s and dot{{m}}_{bh}. finally, there is no strong relation between dot{{m}}_s and eddington ratio, or the asymmetry of the c iv line. the former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with c iv asymmetries arising from orientation effects. | star formation rates in luminous quasars at 2 < z < 3 |
quasars that exhibit blueshifted, broad absorption lines (bal qsos) are an important probe of black hole feedback on galaxy evolution. yet the presence of bals is also a complication for large spectroscopic surveys that use quasars as cosmological probes because the bal features can affect redshift measurements and contaminate information about the matter distribution in the lyα forest. we present a new bal qso catalog for quasars in the sloan digital sky survey (sdss) data release 14 (dr14). as the sdss dr14 quasar catalog has over 500,000 quasars, we have developed an automated bal classifier with a convolutional neural network (cnn). we trained our cnn classifier on the c iv λ 1549 region of a sample of quasars with reliable human classifications, and compared the results to both a dedicated test sample and visual classifications from the earlier sdss dr12 quasar catalog. our cnn classifier correctly classifies over 98% of the bal quasars in the dr12 catalog, which demonstrates comparable reliability to human classification. the disagreements are generally for quasars with lower signal-to-noise ratio spectra and/or weaker bal features. our new catalog includes the probability that each quasar is a bal, the strength, blueshifts and velocity widths of the troughs, and similar information for any si iv λ 1398 bal troughs that may be present. we find significant bal features in 16.8% of all quasars with 1.57 < z < 5.56 in the sdss dr14 quasar catalog. | classification of broad absorption line quasars with a convolutional neural network |
supermassive black hole binaries (smbhbs) should be common in galactic nuclei as a result of frequent galaxy mergers. recently, a large sample of sub-parsec smbhb candidates was identified as bright periodically variable quasars in optical surveys. if the observed periodicity corresponds to the redshifted binary orbital period, the inferred orbital velocities are relativistic (v/c ≈ 0.1). the optical and ultraviolet (uv) luminosities are expected to arise from gas bound to the individual bhs, and would be modulated by the relativistic doppler effect. the optical and uv light curves should vary in tandem with relative amplitudes which depend on the respective spectral slopes. we constructed a control sample of 42 quasars with aperiodic variability, to test whether this doppler colour signature can be distinguished from intrinsic chromatic variability. we found that the doppler signature can arise by chance in ∼20 per cent (∼37 per cent) of quasars in the nuv (fuv) band. these probabilities reflect the limited quality of the control sample and represent upper limits on how frequently quasars mimic the doppler brightness+colour variations. we performed separate tests on the periodic quasar candidates, and found that for the majority, the doppler boost hypothesis requires an unusually steep uv spectrum or an unexpectedly large bh mass and orbital velocity. we conclude that at most approximately one-third of these periodic candidates can harbor doppler-modulated smbhbs. | testing the relativistic doppler boost hypothesis for supermassive black hole binary candidates |
we investigate the cosmic evolution of the black hole (bh) mass-bulge luminosity relation using a sample of 52 active galaxies at z ~ 0.36 and z ~ 0.57 in the bh mass range of 107.4-109.1 m ⊙. by consistently applying multicomponent spectral and structural decomposition to high-quality keck spectra and high-resolution hubble space telescope images, bh masses (m bh) are estimated using the hβ broad emission line combined with the 5100 å nuclear luminosity, and bulge luminosities (l bul) are derived from surface photometry. comparing the resulting m bh - l bul relation to local active galaxies and taking into account selection effects, we find evolution of the form m bh/l bulvprop(1 + z)γ with γ = 1.8 ± 0.7, consistent with bh growth preceding that of the host galaxies. including an additional sample of 27 active galaxies with 0.5 < z < 1.9 taken from the literature and measured in a consistent way, we obtain γ = 0.9 ± 0.7 for the m bh - l bul relation and γ = 0.4 ± 0.5 for the m bh-total host galaxy luminosity (l host) relation. the results strengthen the findings from our previous studies and provide additional evidence for host galaxy bulge growth being dominated by disk-to-bulge transformation via minor mergers and/or disk instabilities. | cosmic evolution of black holes and spheroids. v. the relation between black hole mass and host galaxy luminosity for a sample of 79 active galaxies |
broad emission lines in active galactic nuclei (agns) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. the shape of the broad-line profile, described by {{ d }}{{h}β }={{fwhm}}/{σ }{{h}β }, the ratio of full width at half maximum to the dispersion of broad hβ, reflects the dynamics of the broad-line region (blr) and correlates with the dimensionless accretion rate (\overset{\quad \cdot }{{m}}) or eddington ratio ({l}{{bol}}/{l}{{edd}}). at the same time, \overset{\quad \cdot }{{m}} and {l}{{bol}}/{l}{{edd}} correlate with {{ r }}{{fe}}, the ratio of optical fe ii to hβ line flux emission. assembling all agns with reverberation mapping measurements of broad hβ, both from the literature and from new observations reported here, we find a strong bivariate correlation of the form {log}(\overset{\quad \cdot }{{m}},{l}{{bol}}/{l}{{edd}})=α +β {{ d }}{{h}β }+γ {{ r }}{{fe}}, where α = (2.47, 0.31), β = -(1.59, 0.82), and γ = (1.34, 0.80). we refer to this as the fundamental plane of the blr. we apply the plane to a sample of z < 0.8 quasars to demonstrate the prevalence of super-eddington accreting agns are quite common at low redshifts. | the fundamental plane of the broad-line region in active galactic nuclei |
we present an atlas of mid-infrared (mid-ir) ∼ 7.5-13 μm spectra of 45 local active galactic nuclei (agn) obtained with canaricam on the 10.4 m gran telescopio canarias (gtc) as part of an eso/gtc large programme. the sample includes seyferts and other low-luminosity agn (llagn) at a median distance of 35 mpc and luminous agn, namely pg quasars, (u)lirgs, and radio galaxies (rg) at a median distance of 254 mpc. to date, this is the largest mid-ir spectroscopic catalogue of local agn at sub-arcsecond resolution (median 0.3 arcsec). the goal of this work is to give an overview of the spectroscopic properties of the sample. the nuclear 12 μm luminosities of the agn span more than four orders of magnitude, νl12 μm ∼ 3 × 1041-1046 erg s-1. in a simple mid-ir spectral index versus strength of the 9.7 μm silicate feature diagram most llagn, seyfert nuclei, pg quasars, and rgs lie in the region occupied by clumpy torus model tracks. however, the mid-ir spectra of some might include contributions from other mechanisms. most (u)lirg nuclei in our sample have deeper silicate features and flatter spectral indices than predicted by these models suggesting deeply embedded dust heating sources and/or contribution from star formation. the 11.3 μm polycyclic aromatic hydrocarbon (pah) feature is clearly detected in approximately half of the seyfert nuclei, llagn, and (u)lirgs. while the rg, pg quasars, and (u)lirgs in our sample have similar nuclear νl12 μm, we do not detect nuclear pah emission in the rgs and pg quasars. | a mid-infrared spectroscopic atlas of local active galactic nuclei on sub-arcsecond resolution using gtc/canaricam |
a landmark of accretion processes in active galactic nuclei (agn) is the continuum originating from a complex structure, i.e., an accretion disk and a corona around a supermassive black hole. modelling the broad-band spectral energy distribution (sed) effectively ionizing the gas-rich broad emission line region (blr) is key to understanding the various radiative processes at play and their importance that eventually leads to the emission from diverse physical conditions. photoionization codes are a useful tool to investigate two aspects, the importance of the shape of the spectral energy distribution, and the physical conditions in the broad emission line region. in this work, we critically review long-standing issues pertaining to the spectral energy distribution shape and the anisotropic continuum radiation from the central regions around the accreting supermassive black holes (few 10–100 gravitational radii), with a focus on black holes accreting at high rates, possibly much above the eddington limit. the anisotropic emission is a direct consequence of the development of a geometrically and optically thick structure at regions very close to the black hole due to a marked increase in the accretion rates. the analysis presented in this paper took advantage of the look at the diversity of the type-1 active galactic nuclei provided by the main sequence of quasars. the main sequence permitted us to assess the importance of the eddington ratio and hence to locate the super eddington sources in observational parameter space, as well as to constrain the distinctive physical conditions of their line-emitting blr. this feat is posing the basis for the exploitation of quasars as cosmological distance indicators, hopefully allowing us to use the fascinating super eddington quasars up to unprecedented distances. | high eddington quasars as discovery tools: current state and challenges |
photometric reverberation mapping can detect the radial extent of the accretion disc (ad) in active galactic nuclei by measuring the time delays between light curves observed in different continuum bands. quantifying the constraints on the efficiency and accuracy of the delay measurements is important for recovering the ad size-luminosity relation, and potentially using quasars as standard candles. we have explored the possibility of determining the ad size of quasars using next-generation big data surveys. we focus on the legacy survey of space and time (lsst) at the vera c. rubin observatory, which will observe several thousand quasars with the deep drilling fields and up to 10 million quasars for the main survey in six broadband filter during its 10-yr operational lifetime. we have developed extensive simulations that take into account the characteristics of the lsst survey and the intrinsic properties of the quasars. the simulations are used to characterize the light curves from which ad sizes are determined using various algorithms. we find that the time delays can be recovered with an accuracy of 5 and 15 per cent for light curves with a time sampling of 2 and 5 d, respectively. the results depend strongly on the redshift of the source and the relative contribution of the emission lines to the bandpasses. assuming an optically thick and geometrically thin ad, the recovered time-delay spectrum is consistent with black hole masses derived with 30 per cent uncertainty. | modelling photometric reverberation mapping data for the next generation of big data surveys. quasar accretion discs sizes with the lsst |
we use 13 seasons of r-band photometry from the 1.2 m leonard euler swiss telescope at la silla to examine microlensing variability in the quadruply imaged lensed quasar wfi 2026-4536. the lightcurves exhibit ∼0.2 mag of uncorrelated variability across all epochs and a prominent single feature of ∼0.1 mag within a single season. we analyze this variability to constrain the size of the quasar's accretion disk. adopting a nominal inclination of 60°, we find an accretion disk scale radius of $\mathrm{log}({r}_{s}/\mathrm{cm})={15.74}_{-0.29}^{+0.34}$ at a rest-frame wavelength of 2043 å, and we estimate a black hole mass of $\mathrm{log}({m}_{\mathrm{bh}}/{m}_{\odot })={9.18}_{-0.34}^{+0.39}$ , based on the c iv line in vlt spectra. this size measurement is fully consistent with the quasar accretion disk size—black hole mass relation, providing another system in which the accretion disk is larger than predicted by thin-disk theory. | a microlensing accretion disk size measurement in the lensed quasar wfi 2026-4536 |
we analyze the x-ray, optical, and mid-infrared data of a "changing-look" seyfert galaxy sdss j155258+273728 at z ≃ 0.086. over a period of one decade (2009-2018), its broad hα line intensity increased by a factor of ∼4. meanwhile, the x-ray emission in 2014 as observed by chandra was about five times brighter than that in 2010 by suzaku, and the corresponding emissions in the v-band, mid-infrared w1 band brighten by ∼0.18, 0.32 mag, respectively. moreover, the absorption in x-rays is moderate and stable, i.e., ${n}_{{\rm{h}}}\sim {10}^{21}\ {\mathrm{cm}}^{-2}$ , but the x-ray spectrum becomes harder in the 2014 chandra bright state (i.e., photon index ${\rm{\gamma }}={1.52}_{-0.06}^{+0.06}$ ) than that of the 2010 suzaku low state ( ${\rm{\gamma }}={2.03}_{-0.21}^{+0.22}$ ). with an eddington ratio being lower than a few percent, the inner region of the accretion disk in sdss j155258+273728 is likely a hot accretion flow. we then compile from literature the x-ray data of "changing-look" active galactic nuclei (agns), and find that they generally follow the well-established "v"-shaped correlation in agns, that is, above a critical turnover luminosity the x-ray spectra soften with the increasing luminosity, and below that luminosity the trend is reversed in the way of "harder when brighter." this presents direct evidence that cl-agns have distinctive changes in not only the optical spectral type, but also the x-ray spectral shape. the similarity in the x-ray spectral evolution between cl-agns and black hole x-ray binaries indicates that the observed cl-agns phenomena may relate to the state transition in accretion physics. | x-ray spectral shape variation in changing-look seyfert galaxy sdss j155258+273728 |
we use the simba cosmological hydrodynamic simulation suite to explore the impact of feedback on the circumgalactic medium (cgm) and intergalactic medium (igm) around 2 ≤ z ≤ 3 quasars. we identify quasars in simba as the most rapidly accreting black holes, and show that they are well matched in bolometric luminosity and correlation strength to real quasars. we extract lyα absorption in spectra passing at different transverse distances ( $10 \, \mathrm{kpc} \lesssim b \lesssim 10 \, \rm mpc$ ) around those quasars, and compare to observations of the mean lyα absorption profile. the observations are well reproduced, except within $100 \, \, \rm kpc$ from the foreground quasar, where simba overproduces absorption; this could potentially be mitigated by including ionization from the quasar itself. by comparing runs with different feedback modules activated, we find that (mechanical) agn feedback has little impact on the surrounding cgm even around these most highly luminous black holes, while stellar feedback has a significant impact. by further investigating thermodynamic and kinematic properties of cgm gas, we find that stellar feedback, and not agn feedback, is the primary physical driver in determining the average properties of the cgm around z ∼ 2-3 quasars. we also compare our results with previous works, and find that simba predicts much more absorption within $100 \, \rm kpc$ than the nyx and illustris simulations, showing that the lyα absorption profile can be a powerful constraint on simulations. instruments such as vlt-muse and upcoming surveys (e.g. weave and desi) promise to further improve such constraints. | simba: the average properties of the circumgalactic medium of 2 ≤ z ≤ 3 quasars are determined primarily by stellar feedback |
new methods have recently been developed to search for strong gravitational lenses, in particular lensed quasars, in wide-field imaging surveys. here, we compare the performance of three different, morphology- and photometry-based methods to find lens candidates within the kilo-degree survey (kids) dr3 footprint (440 deg2). the three methods are: i) a multiplet detection in kids-dr3 and/or gaia-dr1, ii) direct modelling of kids cutouts, and iii) positional offsets between different surveys (kids-versus-gaia, gaia-versus-2mass), with purpose-built astrometric recalibrations. the first benchmark for the methods has been set by the recovery of known lenses. we are able to recover seven out of 10 known lenses and pairs of quasars observed in the kids dr3 footprint, or eight out of 10 with improved selection criteria and looser colour pre-selection. this success rate reflects the combination of all methods together, which, taken individually, performed significantly worse (four lenses each). one novelty of our analysis is that the comparison of the performances of the different methods has revealed the strengths and weaknesses of the approaches and, most of all, the complementarity. we finally provide a list of high-grade candidates found by one or more methods, awaiting spectroscopic follow-up for confirmation. of these, kids 1042+0023 is, to our knowledge, the first confirmed lensed quasar from kids, exhibiting two quasar spectra at the same source redshift at either sides of a red galaxy, with uniform flux-ratio f ≈ 1.25 over the wavelength range 0.45 μ m<λ < 0.75 μ m. | kids-squad: the kids strongly lensed quasar detection project |
giant radio galaxies (grgs) are one of the largest astrophysical sources in the universe with an overall projected linear size of ∼0.7 mpc or more. the last six decades of radio astronomy research has led to the detection of thousands of radio galaxies. however, only ∼300 of them can be classified as grgs. the reasons behind their large size and rarity are unknown. we carried out a systematic search for these radio giants and found a large sample of grgs. in this paper, we report the discovery of 25 grgs from the national radio astronomy observatory very large array sky survey, in the red-shift range z ∼ 0.07 to 0.67. their physical sizes range from ∼0.8 mpc to ∼4 mpc. eight of these grgs have sizes ≥2 mpc, which is a rarity. here, for the first time, we investigate the mid-infrared (ir) properties of the optical hosts of the grgs and classify them securely into various active galactic nuclei types using the wise mid-ir colours. using radio and ir data, four of the hosts of the grgs were observed to be radio-loud quasars that extend up to 2 mpc in radio size. these grgs missed detection in earlier searches possibly because of their highly diffuse nature, low surface brightness and lack of optical data. the new grgs are a significant addition to the existing sample. they will contribute to a better understanding of the physical properties of radio giants. | discovery of giant radio galaxies from nvss: radio and infrared properties |
context. radio-loud active galactic nuclei with powerful relativistic jets are thought to be associated with rapidly spinning black holes (bhs). bh spin-up may result from a number of processes, including accretion of matter onto the bh itself, and catastrophic events such as bh-bh mergers.aims: we study the intriguing properties of the powerful (lbol 1047 erg s-1) radio-loud quasar 3c 186. this object shows peculiar features both in the images and in the spectra.methods: we utilize near-ir hubble space telescope (hst) images to study the properties of the host galaxy, and hst uv and sloan digital sky survey optical spectra to study the kinematics of the source. chandra x-ray data are also used to better constrain the physical interpretation.results: hst imaging shows that the active nucleus is offset by 1.3 ± 0.1 arcsec (i.e. 11 kpc) with respect to the center of the host galaxy. spectroscopic data show that the broad emission lines are offset by -2140 ± 390 km s-1 with respect to the narrow lines. velocity shifts are often seen in qso spectra, in particular in high-ionization broad emission lines. the host galaxy of the quasar displays a distorted morphology with possible tidal features that are typical of the late stages of a galaxy merger.conclusions: a number of scenarios can be envisaged to account for the observed features. while the presence of a peculiar outflow cannot be completely ruled out, all of the observed features are consistent with those expected if the qso is associated with a gravitational wave (gw) recoiling bh. future detailed studies of this object will allow us to confirm this type of scenario and will enable a better understanding of both the physics of bh-bh mergers and the phenomena associated with the emission of gw from astrophysical sources. | the puzzling case of the radio-loud qso 3c 186: a gravitational wave recoiling black hole in a young radio source? |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.