- ID:
- ivo://CDS.VizieR/J/ApJ/802/89
- Title:
- Luminosity function of X-ray-selected AGNs
- Short Name:
- J/ApJ/802/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to constrain the evolution of active galactic nuclei (AGNs) as a function of obscuration using an X-ray-selected sample of ~2000 AGNs from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS, and XMM-XXL fields. The spectra of individual X-ray sources are analyzed using a Bayesian methodology with a physically realistic model to infer the posterior distribution of the hydrogen column density and intrinsic X-ray luminosity. We develop a novel non-parametric method that allows us to robustly infer the distribution of the AGN population in X-ray luminosity, redshift, and obscuring column density, relying only on minimal smoothness assumptions. Our analysis properly incorporates uncertainties from low count spectra, photometric redshift measurements, association incompleteness, and the limited sample size. We find that obscured AGNs with N_H_>10^22^/cm2 account for 77_-5_^+4^% of the number density and luminosity density of the accretion supermassive black hole population with L_X_>10^43^erg/s, averaged over cosmic time. Compton-thick AGNs account for approximately half the number and luminosity density of the obscured population, and 38_-7_^+8^% of the total. We also find evidence that the evolution is obscuration dependent, with the strongest evolution around N_H_{approx}10^23^/cm2. We highlight this by measuring the obscured fraction in Compton-thin AGNs, which increases toward z~3, where it is 25% higher than the local value. In contrast, the fraction of Compton-thick AGNs is consistent with being constant at {approx}35%, independent of redshift and accretion luminosity. We discuss our findings in the context of existing models and conclude that the observed evolution is, to first order, a side effect of anti-hierarchical growth.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/786/17
- Title:
- Luminosity functions for 1.3<z<3.2 galaxies
- Short Name:
- J/ApJ/786/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 4.5 {mu}m luminosity functions for galaxies identified in 178 candidate galaxy clusters at 1.3<z<3.2. The clusters were identified as Spitzer/Infrared Array Camera (IRAC) color-selected overdensities in the Clusters Around Radio-Loud AGN project, which imaged 420 powerful radio-loud active galactic nuclei (RLAGNs) at z>1.3. The luminosity functions are derived for different redshift and richness bins, and the IRAC imaging reaches depths of m*+2, allowing us to measure the faint end slopes of the luminosity functions. We find that {alpha}=-1 describes the luminosity function very well in all redshift bins and does not evolve significantly. This provides evidence that the rate at which the low mass galaxy population grows through star formation gets quenched and is replenished by in-falling field galaxies does not have a major net effect on the shape of the luminosity function. Our measurements for m* are consistent with passive evolution models and high formation redshifts (z_f_~3). We find a slight trend toward fainter m* for the richest clusters, implying that the most massive clusters in our sample could contain older stellar populations, yet another example of cosmic downsizing. Modeling shows that a contribution of a star-forming population of up to 40% cannot be ruled out. This value, found from our targeted survey, is significantly lower than the values found for slightly lower redshift, z~1, clusters found in wide-field surveys. The results are consistent with cosmic downsizing, as the clusters studied here were all found in the vicinity of RLAGNs - which have proven to be preferentially located in massive dark matter halos in the richest environments at high redshift - and they may therefore be older and more evolved systems than the general protocluster population.
- ID:
- ivo://CDS.VizieR/J/ApJ/852/72
- Title:
- Luminosity functions of tidal disruption flares
- Short Name:
- J/ApJ/852/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining the observed properties of these events within the tidal disruption paradigm is not yet possible. This theoretical ambiguity has led some authors to suggest that optical TDFs are due to a different process, such as a nuclear supernova or accretion disk instabilities. Here we present a test of a fundamental prediction of the tidal disruption event scenario: a suppression of the flare rate due to the direct capture of stars by the black hole. Using a recently compiled sample of candidate TDFs with black hole mass measurements, plus a careful treatment of selection effects in this flux-limited sample, we confirm that the dearth of observed TDFs from high-mass black holes is statistically significant. All the TDF impostor models we consider fail to explain the observed mass function; the only scenario that fits the data is a suppression of the rate due to direct captures. We find that this suppression can explain the low volumetric rate of the luminous TDF candidate ASASSN-15lh, thus supporting the hypothesis that this flare belongs to the TDF family. Our work is the first to present the optical TDF luminosity function. A steep power law is required to explain the observed rest-frame g-band luminosity, dN/dL_g_{propto}L_g_^-2.5^. The mean event rate of the flares in our sample is ~1x10^-4^galaxy^-1^/yr, consistent with the theoretically expected tidal disruption rate.
- ID:
- ivo://CDS.VizieR/J/ApJ/779/104
- Title:
- Luminous dust-poor SDSS QSOs at z<4.5
- Short Name:
- J/ApJ/779/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify and characterize a population of luminous, dust-poor quasars at 0<z<5 that is photometrically similar to objects previously found at z>6. This class of active galactic nuclei is known to show little IR emission from dusty structure, but it is poorly understood in terms of number evolution and dependence on physical quantities. To better understand the properties of these quasars, we compile a rest-frame UV to IR library of 41000 optically selected type 1 quasars with L_bol_>10^45.7^erg/s. After fitting the broadband spectral energy distributions (SEDs) with accretion disk and dust components, we find 0.6% of our sample to be hot dust-poor, with rest-frame 2.3{mu}m to 0.51{mu}m flux density ratios of -0.5dex or less. The dust-poor SEDs are blue in the UV-optical and weak in the mid-IR, such that their accretion disks are less obscured and the hot dust emission traces that of warm dust down to the dust-poor regime. At a given bolometric luminosity, dust-poor quasars are lower in black hole mass and higher in Eddington ratio than general luminous quasars, suggesting that they are in a rapidly growing evolutionary state in which the dust-poor phase appears as a short or rare phenomenon. The dust-poor fraction increases with redshift, and possible implications for their evolution are discussed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/2817
- Title:
- Luminous Ly{alpha} emitters at z~2-3
- Short Name:
- J/MNRAS/477/2817
- Date:
- 02 Mar 2022 00:40:05
- Publisher:
- CDS
- Description:
- Deep narrow-band surveys have revealed a large population of faint Ly{alpha} emitters (LAEs) in the distant Universe, but relatively little is known about the most luminous sources (L_Lya_>~10^42.7^erg/s; L_Lya>~L^*^_Lya_). Here we present the spectroscopic follow-up of 21 luminous LAEs at z~2-3 found with panoramic narrow-band surveys over five independent extragalactic fields (=~4x10^6^Mpc^3^ surveyed at z~2.2 and z~3.1). We use WHT/ISIS, Keck/DEIMOS, and VLT/X-SHOOTER to study these sources using high ionization UV lines. Luminous LAEs at z~2-3 have blue UV slopes ({beta}=-2.0^+0.3^_-0.1_) and high Ly{alpha} escape fractions (50^+20^_-15_ per cent) and span five orders of magnitude in UV luminosity (M_UV_=~-19 to -24). Many (70 per cent) show at least one high ionization rest-frame UV line such as CIV, NV, CIII], HeII or OIII], typically blue-shifted by =~100-200km/s relative to Ly{alpha}. Their Ly{alpha} profiles reveal a wide variety of shapes, including significant blue-shifted components and widths from 200 to 4000km/s. Overall, 60+/-11 per cent appear to be active galactic nucleus (AGN) dominated, and at L_Lya_>10^43.3^erg/s and/or M_UV_<-21.5 virtually all LAEs are AGNs with high ionization parameters (logU=0.6+/-0.5) and with metallicities of =~0.5-1Z_{sun}_. Those lacking signatures of AGNs (40+/-11 per cent) have lower ionization parameters (logU=-3.0^+1.6^_-0.9_ and log{xi}_ion_=25.4+/-0.2) and are apparently metal-poor sources likely powered by young, dust-poor 'maximal' starbursts. Our results show that luminous LAEs at z~2-3 are a diverse population and that 2xL^*^_Lya_ and 2*M_UV_^*^ mark a sharp transition in the nature of LAEs, from star formation dominated to AGN dominated.
- ID:
- ivo://CDS.VizieR/J/ApJ/829/33
- Title:
- Luminous of high-z QSOs with SDSS and WISE. II
- Short Name:
- J/ApJ/829/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper in a series on a new luminous z~5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar luminosity function (QLF) at z~5. Combining our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z~5 quasar sample to date, with 99 quasars in the range of 4.7<=z<5.4 and -29<M_1450_<=-26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/V_a_ method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as {alpha}=-2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope {beta}=-3.58+/-0.24 and a fainter break magnitude M_1450_^*^=-26.98+/-0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution model. Using the best-fit QLF, the contribution of quasars to the ionizing background at z~5 is found to be 18%-45% with a clumping factor C of 2-5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/44
- Title:
- Luminous persistent sources in nearby galaxies search
- Short Name:
- J/ApJ/846/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sources in nearby galaxies, with radio luminosities >10% of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within <108Mpc, in a footprint of 10600deg^2^. After rejecting sources likely due to active galactic nuclei activity or background sources, I am left with 11 candidates that are presumably associated with galactic disks or star-formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within 1" of galactic nuclei. Assuming that the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of <~5x10^-5^Mpc^-3^, and that at any given time only a small fraction of galaxies host a radio-luminous persistent source (<~10^-3^L_*_^-1^). Assuming a persistent source lifetime of 100 years, this implies a birth rate of <~5x10^-7^yr^-1^Mpc^-3^. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of >~0.8yr^-1^. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.
- ID:
- ivo://CDS.VizieR/J/ApJ/861/37
- Title:
- Luminous WISE-selected quasars in SDSS Stripe 82
- Short Name:
- J/ApJ/861/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopically complete sample of 147 infrared-color-selected active galactic nuclei (AGNs) down to a 22{mu}m flux limit of 20mJy over the ~270deg^2^ of the Sloan Digital Sky Survey Stripe 82 region. Most of these sources are in the QSO luminosity regime (Lbol>~10^12^L_{sun}_) and are found out to z~3. We classify the AGNs into three types, finding 57 blue, unobscured Type-1 (broad-lined) sources; 69 obscured, Type-2 (narrow-lined) sources; and 21 moderately reddened Type-1 sources (broad-lined and E(B-V)>0.25). We study a subset of this sample in X-rays and analyze their obscuration to find that our spectroscopic classifications are in broad agreement with low, moderate, and large amounts of absorption for Type-1, red Type-1, and Type-2 AGNs, respectively. We also investigate how their X-ray luminosities correlate with other known bolometric luminosity indicators such as [OIII] line luminosity (L[OIII]) and infrared luminosity (L6{mu}m). While the X-ray correlation with L[OIII] is consistent with previous findings, the most infrared-luminous sources appear to deviate from established relations such that they are either underluminous in X-rays or overluminous in the infrared. Finally, we examine the luminosity function evolution of our sample, and by AGN type, in combination with the complementary, infrared-selected, AGN sample of Lacy et al. (2013), spanning over two orders of magnitude in luminosity. We find that the two obscured populations evolve differently, with reddened Type-1 AGNs dominating the obscured AGN fraction (~30%) for L_5{mu}m_>10^45^erg/s, while the fraction of Type-2 AGNs with L_5{mu}m_<10^45^erg/s rises sharply from 40% to 80% of the overall AGN population.
- ID:
- ivo://CDS.VizieR/J/ApJ/888/89
- Title:
- Lya galaxies in 3 CFHTLS overdense regions
- Short Name:
- J/ApJ/888/89
- Date:
- 25 Oct 2021 10:16:31
- Publisher:
- CDS
- Description:
- We have carried out follow-up spectroscopy on three overdense regions of g- and r-dropout galaxies in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields, finding two new protoclusters at z=4.898 and 3.721 and a possible protocluster at z=3.834. The z=3.721 protocluster overlaps with a previously identified protocluster at z=3.675. The redshift separation between these two protoclusters is {Delta}z=0.05, which is slightly larger than the size of typical protoclusters. Therefore, if they are not the progenitors of a >10^15^M_{sun}_ halo, they would grow into closely located independent halos like a supercluster. The other protocluster at z=4.898 is also surrounded by smaller galaxy groups. These systems including protoclusters and neighboring groups are regarded as the early phase of superclusters. We quantify the spatial distribution of member galaxies of the protoclusters at z=3.675 and 3.721 by fitting triaxial ellipsoids, finding a tentative difference: one has a pancake-like shape, while the other is filamentary. This could indicate that these two protoclusters are in different stages of formation. We investigate the relation between redshift and the velocity dispersion of protoclusters, including other protoclusters from the literature, in order to compare their dynamical states. Although there is no significant systematic trend in the velocity dispersions of protoclusters with redshift, the distribution is skewed to higher velocity dispersion over the redshift range of z=2-6. This could be interpreted as two phases of cluster formation, one dominated by the steady accretion of galaxies and the other by the merging between group-size halos, perhaps depending on the surrounding large-scale environments.
- ID:
- ivo://CDS.VizieR/J/ApJ/559/654
- Title:
- Ly{alpha} absorption systems. V.
- Short Name:
- J/ApJ/559/654
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Here we present the additional HST WFPC2 observations of galaxies in 10 QSO fields that were not included in Paper I (Chen et al., 1998, Cat. <J/ApJ/498/77>) and near-infrared imaging observations of galaxies in 15 QSO fields.
