ABSTRACT We characterize the optical variability of quasars in the Palomar Transient Factory and intermediate Palomar Transient Factory (PTF/iPTF) surveys. We re-calibrate the r-band light curves for ...∼28,000 luminous, broad-line active galactic nuclei from the SDSS, producing a total of ∼2.4 million photometric data points. We utilize both the structure function (SF) and power spectrum density (PSD) formalisms to search for links between the optical variability and the physical parameters of the accreting supermassive black holes that power the quasars. The excess variance (SF2) of the quasar sample tends to zero at very short time separations, validating our re-calibration of the time-series data. We find that the the amplitude of variability at a given time-interval, or equivalently the timescale of variability to reach a certain amplitude, is most strongly correlated with luminosity with weak or no dependence on black hole mass and redshift. For a variability level of SF(τ) = 0.07 mag, the timescale has a dependency of . This is broadly consistent with the expectation from a simple Keplerian accretion disk model, which provides . The PSD analysis also reveals that many quasar light curves are steeper than a damped random walk. We find a correlation between the steepness of the PSD slopes, specifically the fraction of slopes steeper than 2.5, and black hole mass, although we cannot exclude the possibility that luminosity or Eddington ratio are the drivers of this effect. This effect is also seen in the SF analysis of the (i)PTF data, and in a PSD analysis of quasars in the SDSS Stripe 82.
Abstract
We examine the contribution of high-redshift (
z
> 6) active galactic nuclei (AGNs) to cosmic hydrogen reionization, by tracing the growth and ionizing output of the first generation of ...supermassive black holes (SMBHs). Our calculations are anchored to the observed population of
z
≃ 6 quasars, and trace back the evolving spectral energy distributions (SEDs) of the accretion flows that power these early AGNs and consider a variety of growth histories, including super-Eddington accretion. Compared to a fixed-shape SED, the evolving thin disks produce ionizing radiation that is higher by up to ∼80%. Across a variety of SMBH growth scenarios, the contribution of AGNs to reionization is limited to late epochs (
z
< 7), and remains subdominant compared to star-forming galaxies. This conclusion holds irrespective of the (still unknown) space density of low-luminosity
z
= 6 AGNs, and for growth scenarios that allow super-Eddington accretion. The contribution of AGNs to reionization can extend to earlier epochs (
z
≳ 8) in scenarios with relatively slow SMBH mass growth, i.e., for low accretion rates and/or high spins. We finally demonstrate that our framework can reproduce the observed quasar proximity-zone sizes, and that compact proximity zones around
z
= 6 quasars can be explained by the late onset of super-Eddington accretion.
We estimate the accretion rates onto the supermassive black holes that power 20 of the highest-redshift quasars, at , including the quasar with the highest redshift known to date-ULAS J1120 at z = ...7.09. The analysis is based on the observed (rest-frame) optical luminosities and reliable "virial" estimates of the BH masses of the quasars, and utilizes scaling relations derived from thin accretion disk theory. The mass accretion rates through the postulated disks cover a wide range, , with most of the objects (80%) having , confirming the Eddington-limited nature of the accretion flows. By combining our estimates of with conservative, lower limits on the bolometric luminosities of the quasars, we investigate which alternative values of best account for all the available data. We find that the vast majority of quasars (∼85%) can be explained with radiative efficiencies in the range , with a median value close to the commonly assumed = 0.1. Within this range, we obtain conservative estimates of for ULAS J1120 and SDSS J0100 (at z = 6.3), and of for SDSS J1148 (at assuming their BH masses are accurate). The implied accretion timescales are generally in the range , suggesting that most quasars could have had mass e-foldings since BH seed formation. Our analysis therefore demonstrates that the available luminosities and masses for the highest-redshift quasars can be explained self-consistently within the thin, radiatively efficient accretion disk paradigm. Episodes of radiatively inefficient, "super-critical" accretion may have occurred at significantly earlier epochs (i.e., ).
We present new ALMA band-7 data for a sample of six luminous quasars at , powered by fast-growing supermassive black holes (SMBHs) with rather uniform properties: the typical accretion rates and ...black hole masses are and . Our sample consists of three "FIR-bright" sources, which were individually detected in previous Herschel/SPIRE observations, with star formation rates of , and three "FIR-faint" sources for which Herschel stacking analysis implies a typical SFR of ∼400 . The dusty interstellar medium in the hosts of all six quasars is clearly detected in the ALMA data and resolved on scales of ∼2 kpc, in both continuum ( ) and line emission. The continuum emission is in good agreement with the expectations from the Herschel data, confirming the intense SF activity in the quasar hosts. Importantly, we detect companion sub-millimeter galaxies (SMGs) for three sources-one FIR-bright and two FIR-faint, separated by and from the quasar hosts. The -based dynamical mass estimates for the interacting SMGs are within a factor of ∼3 of the quasar hosts' masses, while the continuum emission implies . Our ALMA data therefore clearly support the idea that major mergers are important drivers for rapid early SMBH growth. However, the fact that not all high-SFR quasar hosts are accompanied by interacting SMGs and the gas kinematics as observed by ALMA suggest that other processes may be fueling these systems. Our analysis thus demonstrates the diversity of host galaxy properties and gas accretion mechanisms associated with early and rapid SMBH growth.
The 105-Month Swift-BAT All-sky Hard X-Ray Survey Oh, Kyuseok; Koss, Michael; Markwardt, Craig B. ...
The Astrophysical journal. Supplement series,
03/2018, Letnik:
235, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present a catalog of hard X-ray sources detected in the first 105 months of observations with the Burst Alert Telescope (BAT) coded-mask imager on board the Swift observatory. The 105-month ...Swift-BAT survey is a uniform hard X-ray all-sky survey with a sensitivity of over 90% of the sky and over 50% of the sky in the 14-195 keV band. The Swift-BAT 105-month catalog provides 1632 (422 new detections) hard X-ray sources in the 14-195 keV band above the significance level. Adding to the previously known hard X-ray sources, 34% (144/422) of the new detections are identified as Seyfert active galactic nuclei (AGNs) in nearby galaxies ( ). The majority of the remaining identified sources are X-ray binaries (7%, 31) and blazars/BL Lac objects (10%, 43). As part of this new edition of the Swift-BAT catalog, we release eight-channel spectra and monthly sampled light curves for each object in the online journal and at the Swift-BAT 105-month website.
In order to relate the observed evolution of the galaxy stellar mass function and the luminosity function of active galactic nuclei (AGNs), we explore a coevolution scenario in which AGNs are ...associated only with the very last phases of the star-forming life of a galaxy. We derive analytically the connections between the parameters of the observed quasar luminosity functions and galaxy mass functions. The (mbh/m*)Qing associated with quenching is given by the ratio of the global black hole accretion rate density (BHARD) and star formation rate density (SFRD) at the epoch in question. Observational data on the SFRD and BHARD suggest (mbh/m*)Qing ∝ (1 + z)1.5 below redshift 2. This evolution reproduces the observed mass-luminosity plane of Sloan Digital Sky Survey quasars, as well as the local mbh/m* relation in passive galaxies. The characteristic Eddington ratio, λ*, is derived from both the BHARD/SFRD ratio and the evolving L* of the AGN population. This increases up to z ∼ 2 as λ* ∝ (1 + z)2.5, but at higher redshifts, λ* stabilizes at the physically interesting Eddington limit, λ* ∼ 1. The new model may be thought of as an opposite extreme to our earlier coevolution scenario in Caplar et al. The main observable difference between the two coevolution scenarios, presented here and in Caplar et al. is in the active fraction of low-mass star-forming galaxies. We compare the predictions with the data from deep multiwavelength surveys and find that the "quenching" scenario developed in the current paper is preferred.
ABSTRACT We report Herschel/SPIRE observations of 100 very luminous, optically selected active galactic nuclei (AGNs) at with (erg s−1) ≥ 46.5 , where is λLλ at 1350 . The distribution in is similar ...to the general distribution of Sloan Digital Sky Survey AGNs in this redshift and luminosity interval. We measured star-formation (SF) luminosity, , and SF rate (SFR) in 34 detected sources by fitting combined SF and torus templates, where the torus emission is based on Wide Field Infrared Survey Explorer observations. We also obtained statistically significant stacks for the undetected sources in two luminosity groups. The sample properties are compared with those of very luminous AGNs at . The main findings are: (1) The mean and the median SFRs of the detected sources are and M yr−1, respectively. The mean SFR of the undetected sources is 148 M yr−1. The ratio of SFR to the black hole accretion rate is 80 for the detected sources and less than 10 for the undetected sources. Unlike a sample of sources at z 4.8 that we studied recently, there is no difference in and only a very small difference in between the detected and undetected sources. (2) The redshift distribution of and for the most luminous, redshift 2-7 AGNs are different. Similar to previous studies, the highest are found at z 3. However, the of such sources peaks at z 5. Assuming the objects in our sample are hosted by the most massive galaxies at those redshifts, we find that approximately 2/3 of the hosts are already below the main sequence of SF galaxies at z = 2−3.5. (3) The spectral energy distributions (SEDs) of dusty tori at high redshift are similar to the shapes found in low redshift, low luminosity AGNs. Herschel upper limits put strong constraints on the long wavelength shape of the SED, ruling out several earlier suggested torus templates as applicable for this sample. (4) We find no evidence for a luminosity dependence of the torus covering factor in sources with (erg s−1) = 44−47.5. This conclusion is based on the recognition that the estimated in several earlier studies is highly uncertain and non-uniformally treated. The median covering factors over this range are 0.68 for isotropic dust emission and 0.4 for anisotropic emission.
We systematically investigate the near- to far-infrared (FIR) photometric properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope ...(BAT) all-sky ultra-hard X-ray (14-195 keV) survey. Out of 606 non-blazar AGNs in the Swift/BAT 70 month catalog at high galactic latitudes of , we obtain IR photometric data of 604 objects by cross-matching the AGN positions with catalogs from the WISE, AKARI, IRAS, and Herschel infrared observatories. We find a good correlation between the ultra-hard X-ray and mid-IR luminosities over five orders of magnitude ( ). Informed by previous measurements of the intrinsic spectral energy distribution of AGNs, we find FIR pure-AGN candidates whose FIR emission is thought to be AGN-dominated with low star-formation activity. We demonstrate that the dust covering factor decreases with the bolometric AGN luminosity, confirming the luminosity-dependent unified scheme. We also show that the completeness of the WISE color-color cut in selecting Swift/BAT AGNs increases strongly with 14-195 keV luminosity.
We present the first catalog and data release of the Swift-BAT AGN Spectroscopic Survey. We analyze optical spectra of the majority of the detected AGNs (77%, 642/836)based on their 14-195 keV ...emission in the 70-month Swift-BAT all-sky catalog. This includes redshift determination, absorption and emission-line measurements, and black hole mass and accretion rate estimates for the majority of obscured and unobscured AGNs (74%, 473/642), with 340 measured for the first time. With ∼90% of sources at , the survey represents a significant advance in the census of hard X-ray-selected AGNs in the local universe. In this first catalog paper, we describe the spectroscopic observations and data sets, and our initial spectral analysis. The FWHMs of the emission lines show broad agreement with the X-ray obscuration (∼94%), such that Sy 1-1.8 have cm−2, and Seyfert 2 have cm−2. Seyfert 1.9, however, show a range of column densities. Compared to narrow-line AGNs in the SDSS, the X-ray-selected AGNs have a larger fraction of dusty host galaxies ( ), suggesting that these types of AGN are missed in optical surveys. Using the O iii λ5007/Hβ and N ii λ6583/H emission-line diagnostic, about half of the sources are classified as Seyferts; ∼15% reside in dusty galaxies that lack an Hβ detection, but for which the upper limits on line emission imply either a Seyfert or LINER, are in galaxies with weak or no emission lines despite high-quality spectra, and a few percent each are LINERS, composite galaxies, H ii regions, or in known beamed AGNs.
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