FIRST Bright Quasar Survey Research Articles

STRONG VARIABILITY OF OVERLAPPING IRON BROAD ABSORPTION LINES IN FIVE RADIO-SELECTED QUASARS

We present the variability study of broad absorption lines (BALs) in a uniformly radio-selected sample of 28 BAL quasars using the archival data from the FIRST Bright Quasar Survey (FBQS) and the Sloan Digital Sky Survey (SDSS), as well as those obtained by ourselves, covering time scales $\sim 1-10$ years in the quasar's rest-frame. To our surprise, 5 quasars showing strong variations are all belong to a special subclass of overlapping iron low ionization BAL (OFeLoBAL) quasars, however, other 4 non-overlapping FeLoBALs (non-OFeLoBALs) are invariable except one case with weak optical depth change. Meanwhile, we also find 6 typical variations of high-ionization and low-ionization BALs in this BAL quasar sample. Photoionization models suggest that OFeLoBALs are formed in a relative dense ($n_e>10^6$ cm$^{-3}$) outflows at a distance from the subparsec to the dozens of parsecs from the continuum source. They differ from those of non-OFeLoBALs, which are likely produced by low-density gas, locating at a distance of hundreds to thousands parsecs. Thus, OFeLoBALs and non-OFeLoBALs, i.e., FeLoBALs with/without strong BAL variations, perhaps represent the bimodality of Fe II absorption, the former is located in the active galactic nucleus environment rather than the host galaxy. We suggest that high density and small distance are the necessary conditions that cause OFeLoBALs. As suggested in the literature, strong BAL variability is possibly due to variability of the covering factor of BAL regions caused by clouds transiting across the line of sight rather than ionization variations.

A PERIODICALLY VARYING LUMINOUS QUASAR AT z = 2 FROM THE PAN-STARRS1 MEDIUM DEEP SURVEY: A CANDIDATE SUPERMASSIVE BLACK HOLE BINARY IN THE GRAVITATIONAL WAVE-DRIVEN REGIME

Supermassive black hole binaries (SMBHBs) should be an inevitable consequence of the hierarchical growth of massive galaxies through mergers, and the strongest sirens of gravitational waves (GWs) in the cosmos. And yet, their direct detection has remained elusive due to the compact (sub-parsec) orbital separations of gravitationally bound SMBHBs. Here we exploit a theoretically predicted signature of a SMBHB in the time domain: periodic variability caused by a mass accretion rate that is modulated by the binary's orbital motion. We report our first significant periodically varying quasar detection from the systematic search in the Pan-STARRS1 (PS1) Medium Deep Survey. Our SMBHB candidate, PSO J334.2028+01.4075, is a luminous radio-loud quasar at $z=2.060$, with extended baseline photometry from the Catalina Real-Time Transient Survey, as well as archival spectroscopy from the FIRST Bright Quasar Survey. The observed period ($542 \pm 15$ days) and estimated black hole mass ($\log (M_{\rm BH}/M_\odot) = 9.97 \pm 0.50$), correspond to an orbital separation of $7^{+8}_{-4}$ Schwarzschild radii ($\sim 0.006^{+0.007}_{-0.003}$ pc), assuming the rest-frame period of the quasar variability traces the orbital period of the binary. This SMBHB candidate, discovered at the peak redshift for SMBH mergers, is in a physically stable configuration for a circumbinary accretion disk, and within the regime of GW-driven orbital decay. Our search with PS1 is a benchmark study for the exciting capabilities of LSST, which will have orders of magnitude larger survey power, and will potentially pinpoint the locations of thousands of SMBHBs in the variable night sky.

Properties of radio-detected broad absorption line quasars from the Sloan Digital Sky Survey

We investigate the optical colors and radio morphologies of 214 broad absorption line (BAL) quasars with FIRST detections in the redshift range 1.68≤z≤4.93 drawn from the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) quasar catalog. The radio-detected SDSS BAL quasars are found to have Δ(g−i) colors significantly redder than their non-BAL counterparts, with a mean color difference of 0.52 mag, in good agreement with the O–E (roughly B–R) color difference between radio-selected BAL and non-BAL quasars in the FIRST Bright Quasar Survey (FBQS). The vast majority (∼90 %) of the radio-detected BAL quasars are found to be core-only sources, most of which show compact radio morphologies, consistent with the morphological results for the FBQS sample. Moreover, within the FIRST-detected SDSS sample, BAL quasars with GB6 detections are found to span a wide range in radio spectral indices, indistinguishable from that of non-BAL quasars, indicating no special line of sight for the presence of BALs. The properties of the present SDSS sample are more consistent with the evolutionary model, in which BALs are at an early evolutionary stage of quasars.

FR II Broad Absorption Line Quasars and the Life Cycle of Quasars

By combining the Sloan Digitized Sky Survey Third Data Release quasar list with the VLA FIRST survey, we have identified five objects having both broad absorption lines in their optical spectra and FR-II radio morphologies. We identify an additional example of this class from the FIRST Bright Quasar Survey, J1408+3054. Including the original FR-II-BAL object, J1016+5209, brings the number of such objects to eight. These quasars are relatively rare; finding this small handful has required the 45,000-large quasar sample of SDSS. The FR-II-BAL quasars exhibit a significant anti-correlation between radio-loudness and the strength of the BAL features. This is easily accounted for by the evolutionary picture in which quasars emerge from cocoons of BAL-producing material which stifle the development of radio jets and lobes. There is no such simple explanation for the observed properties of FR-II-BALs in the unification-by-orientation model of quasars. The rarity of the FR-II-BAL class implies that the two phases do not coexist for very long in a single quasar, perhaps less than 10{sup 5} years, with the combined FR-II, high ionization broad absorption phase being even shorter by another factor of 10 or more.

Optical Properties of Radio-selected Narrow-Line Seyfert 1 Galaxies

We present results from the analysis of the optical spectra of 47 radio-selected narrow-line Seyfert 1 galaxies (NLS1s). These objects are a subset of the First Bright Quasar Survey (FBQS) and were initially detected at 20 cm (flux density limit {approx} 1 mJy) in the VLA FIRST Survey. We run Spearman rank correlation tests on several sets of parameters and conclude that, except for their radio properties, radio-selected NLS1 galaxies do not exhibit significant differences from traditional NLS1 galaxies. Our results are also in agreement with previous studies suggesting that NLS1 galaxies have small black hole masses that are accreting very close to the Eddington rate. We have found 16 new radio-loud NLS1 galaxies, which increases the number of known radio-loud NLS1 galaxies by a factor of {approx} 5.

AnI-Band-selected Sample of Radio-emitting Quasars: Evidence for a Large Population of Red Quasars

We have constructed a sample of quasar candidates by comparing the FIRST radio survey with the 16 deg2 Deeprange I-band survey carried out by Postman and coworkers. Spectroscopic follow-up of this magnitude-limited sample [I < 20.5, Fν(20 cm) > 1 mJy] has revealed 35 quasars, all but two of which are reported here for the first time. This sample contains some unusual broad absorption line (BAL) quasars, including the first radio-loud FR II BAL previously reported by Gregg and coworkers. Comparison of this sample with the FIRST Bright Quasar survey samples selected in a somewhat bluer band and with brighter magnitude limits reveals that the I-band–selected sample is redder by 0.25–0.5 mag in B-R and that the color difference is not explained by the higher mean redshift of this sample but must be intrinsic. Our small sample contains five quasars with unusually red colors, including three that appear very heavily reddened. Our data are fitted well with normal blue quasar spectra attenuated by more than 2.5 mag of extinction in the I band. These red quasars are only seen at low redshifts (z < 1.3). Even with a magnitude limit I < 20.5, our survey is deep enough to detect only the most luminous of these red quasars at z ≲ 1; similar objects at higher redshifts would fall below our I-band limit. Indeed, the five most luminous objects (using dereddened magnitudes) with z < 1.3 are all red. Our data strongly support the hypothesis that radio quasars are dominated by a previously undetected population of red, heavily obscured objects. Unless highly reddened quasars are preferentially also highly luminous, there must be an even larger, as yet undiscovered, population of red quasars at lower luminosity. We are likely to be finding only the most luminous tip of the red quasar iceberg. A comparison of the positions of the objects in our sample with the catalog of Deeprange cluster candidates reveals that five of our six z < 1 quasars are associated with cluster candidates of similar estimated redshifts. This association is very unlikely to be the result of chance. It has some surprising implications, including the possibility that up to half of the Deeprange clusters at z ∼ 1 have associated quasars.

Decline of the Space Density of Quasars betweenz= 2 andz= 4

We define a new complete sample of 13 optically luminous radio quasars [MAB(1450 A) 25.7] with redshift 3.8 < z < 4.5, obtained by cross-correlating the Faint Images of the Radio Sky at Twenty cm (FIRST) radio survey and the Automatic Plate Measuring Facility catalog of POSS I. We measure the space density to be 1.0 ± 0.3 Gpc-3, a factor of 1.9 ± 0.7 smaller than the space density of similar quasars at z ≈ 2 (FIRST Bright Quasar Survey). Using a new measurement of the radio-loud fraction of quasars, we find that at z = 4 the total space density of quasars with MAB(1450 A) < -26.9 mag is 7.4 ± 2.6 Gpc-3. This is a factor of 1.8 ± 0.8 less than the space density at z ≈ 2, found by the Two-Degree Field quasar survey. This z = 2/z = 4 ratio, consistent with that of the radio-loud quasars, is significantly different from the ratio of ~10 found for samples including lower luminosity quasars. This suggests that the decline of the space density beyond z ≈ 2 is slower for optically luminous quasars than for less luminous ones.

The Frequency and Radio Properties of Broad Absorption Line Quasars

A sample of 67 broad absorption line quasars (BALQSOs) from the Large Bright Quasar Survey (LBQS) is used to estimate the observed and intrinsic fraction of BAL quasars in optically selected samples at intermediate (BJ ≃ 18.5) magnitudes. The observed BALQSO fraction in the redshift range 1.5 ≤ z ≤ 3.0 is 15% ± 3%. A well-determined empirical k-correction, to allow for the differences in the spectral energy distributions of non-BALQSOs and BALQSOs shortward of ≃2100 Å in the rest frame, is applied to the sample. The result is an estimate of the intrinsic fraction of BALQSOs of 22% ± 4% for the redshift range 1.5 ≤ z ≤ 3.0. This value is twice that commonly cited for the occurrence of BALQSOs in optically selected samples, and the figure is in reasonable agreement with that from a preliminary analysis of the SDSS Early Data Release. The fraction of BALQSOs predicted to be present in an optical survey with flux limits equivalent to that of the FIRST Bright Quasar Survey (FBQS) is shown to be ≃20%. The BALQSO fractions derived from the FBQS and the LBQS suggest that optically bright BALQSOs are half as likely as non-BALQSOs to be detectable as S1.4 GHz ≳ 1 mJy radio sources.

A survey for large-separation lensed FIRST quasars -- II. Magnification bias and redshift distribution

The statistics of large-separation gravitational lensing are a powerful tool for probing mass distributions on the scale of galaxy clusters. In this paper we refine the analysis of our survey for large-separation (>5 arcsec) lensed FIRST quasars by estimating the magnification bias and the source redshift distribution. Finding no large-separation lens among 8000 probable quasars in that sample implies an upper bound on the lensed fraction of 3.7 x 10 - 4 at 95 per cent confidence level. From a published deep 1.4-GHz radio survey of the Hubble Deep Field, and corresponding optical searches for faint quasars, we calculate a lower limit to the 'double-flux magnification bias' affecting our radio-optically selected sample, of B ≥ 1.1. From the four-colour information in the SDSS Early Data Release, we calculate the photometric-redshift distribution of a sample of FIRST quasar candidates and compare it with the redshift distribution from the FIRST Bright Quasar Survey. We find that the median redshift of the quasars in our sample is approximately 1.4. With these new results, we find that for all plausible cosmologies, the absence of lensed quasars in our survey is consistent with a model based on an empirical, non-evolving, cluster mass function, where clusters are represented by singular isothermal spheres. On the other hand, comparison of our results with the lensing predictions of published N-body ray-tracing simulations rejects the COBE normalized Ω 0 = 1 cold dark matter model at 99.9 per cent confidence.

Broad Absorption Line Quasars in the Sloan Digital Sky Survey with VLA FIRST Radio Detections

We present 13 broad absorption line (BAL) quasars, including 12 new objects, identi—ed in the Sloan Digital Sky Survey (SDSS) and matched within 2A to sources in the FIRST radio survey catalog. The surface density of this sample of radio-detected BAL quasars is 4.5 ^ 1.2 per 100 deg2, i.e., approximately 4 times as high as previously found by the shallower FIRST Bright Quasar Survey (FBQS). A majority of these radio-detected BAL quasars are moderately radio-loud objects. The fraction of BAL quasars in the entire radio quasar sample, 4.8% ^ 1.3%, is comparable to the fraction of BAL quasars among the SDSS optical quasar sample (ignoring selection eUects). We estimate that the true fraction of BAL quasars (mostly ii HiBALs ˇˇ) in the radio sample is 9.2% ^ 2.6%, once selection eUects are accounted for. We caution that the absorption troughs of four of the 13 radio-detected quasars considered do not strictly satisfy the standard BALnicity criteria. One or possibly two of the new radio-detected BAL quasars are of the rare ii FeLoBAL ˇˇ type. BAL quasars are generally redder than the median SDSS quasar at the same redshift. ”

The FIRST Bright Quasar Survey. III. The South Galactic Cap

We present the results of an extension of the FIRST Bright Quasar Survey (FBQS) to the South Galactic cap, and to a fainter optical magnitude limit. Radio source counterparts with SERC R magnitudes brighter than 18.9 which meet the other FBQS criteria are included. We supplement this list with a modest number of additional objects to test our completeness for quasars with extended radio morphologies. The survey covers 589 deg2 in two equatorial strips in the southern cap. We have obtained spectra for 86% of the 522 candidates and find 321 radio-selected quasars of which 264 are reported here for the first time. A comparison of this fainter sample with the FBQS sample shows the two to be generally similar. Fourteen new broad absorption line (BAL) quasars are included in this sample. When combined with the previously identified BAL quasars in our earlier papers, we can discern a break in the frequency of BAL quasars with radio loudness, namely that the relative number of high-ionization BAL quasars drops by a factor of 4 for quasars with a radio-loudness parameter R* > 100.

The Radio Luminosity–Black Hole Mass Correlation for Quasars from the FIRST Bright Quasar Survey and a “Unification Scheme” for Radio-loud and Radio-quiet Quasars

Several independent lines of evidence now point to a correlation between black hole mass Mbh and radio luminosity. In this Letter, we discuss the correlation for quasars from the FIRST Bright Quasar Survey (FBQS) using black hole mass estimates from Hβ line widths. The FBQS objects fill in the gap between the radio-loud and radio-quiet quasars in the radio luminosity-optical luminosity plane, and we find that they fill the corresponding gap in the Mbh-radio luminosity correlation. There is thus a continuous variation of radio luminosity with Mbh, and no evidence for a switch at some set of critical parameter values that turns on powerful radio jets. By combining the FBQS data with that for quasars from the Palomar-Green survey, we find evidence for a dependence of radio luminosity on accretion rate relative to the Eddington limit, L/LEdd, as well as on Mbh, consistent with the well-known radio-optical correlation for radio-loud quasars. We therefore suggest a new scheme to unify radio-loud and radio-quiet objects in which the radio luminosity scales proportional to M(L/LEdd)1.0 for L/LEdd ~ 0.1, with an apparently weaker accretion rate dependence at low L/LEdd. The scatter about this relation is ±1.1 dex and may well hide significant contributions from other physical effects, such as the black hole spin and radio source environment.

Long-Term Optical Variability of Radio-selected Quasars from the FIRST Survey

We have obtained single-epoch optical photometry for 201 quasars, taken from the FIRST Bright Quasar Survey, which span a wide range in radio loudness. Comparison with the magnitudes of these objects on the POSS-I plates provides by far the largest sample of long-term variability amplitudes for radio-selected quasars yet produced. We find the quasars to be more variable in the blue than in the red band, consistent with work on optically selected samples. The previously noted trend of decreasing variability with increasing optical luminosity applies only to radio-quiet objects. Furthermore, we do not confirm a rise in variability amplitude with redshift, nor do we see any dependence on radio flux or luminosity. The variability over a radio-optical flux ratio range spanning a factor of 60,000 from radio-quiet to extreme radio-loud objects is largely constant, although there is a suggestion of greater variability in the extreme radio-loud objects. We demonstrate the importance of Malmquist bias in variability studies, and develop a procedure to correct for the bias in order to reveal the underlying variability properties of the sample.

Composite Spectra from the FIRST Bright Quasar Survey

We present a very high signal-to-noise ratio composite spectrum created using 657 radio-selected quasars from the FIRST Bright Quasar Survey. The spectrum spans rest-frame wavelengths 900 - 7500 Angstroms. Additionally we present composite spectra formed from subsets of the total data set in order to investigate the spectral dependence on radio loudness and the presence of broad absorption. In particular, radio-loud quasars are red compared to radio-quiet quasars, and quasars showing low-ionization broad absorption lines are red compared to other quasars. We compare our composites with those from the Large Bright Quasar Survey. Composite quasar spectra have proven to be valuable tools for a host of applications, and in that spirit we make these publically available via the FIRST survey web page.

Properties of Radio‐selected Broad Absorption Line Quasars from the First Bright Quasar Survey

In a spectroscopic follow-up to the VLA FIRST survey, the FIRST Bright Quasar Survey (FBQS) has found 29 radio-selected broad absorption line (BAL) quasars. This sample provides the first opportunity to study the properties of radio-selected BAL quasars. Contrary to most previous studies, we establish that a significant population of radio-loud BAL quasars exists. Radio-selected BAL quasars display compact radio morphologies and possess both steep and flat radio spectra. Quasars with low-ionization BALs have a color distribution redder than that of the FBQS sample as a whole. The frequency of BAL quasars in the FBQS is significantly greater, perhaps by as much as a factor of two, than that inferred from optically selected samples. The frequency of BAL quasars appears to have a complex dependence on radio-loudness. The properties of this sample appear inconsistent with simple unified models in which BAL quasars constitute a subset of quasars seen edge-on.

The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later

We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as the basis for constructing a new radio-selected sample of optically bright quasars. This is the first radio-selected sample that is competitive in size with current optically selected quasar surveys. Using only two basic criteria, radio-optical positional coincidence and optical morphology, quasars and BL Lacs can be identified with 60% selection efficiency; the efficiency increases to 70% for objects fainter than magnitude 17. We show that a more sophisticated selection scheme can predict with better than 85% reliability which candidates will turn out to be quasars. This paper presents the second installment of the FIRST Bright Quasar Survey with a catalog of 636 quasars distributed over 2682 square degrees. The quasar sample is characterized and all spectra are displayed. The FBQS detects both radio-loud and radio-quiet quasars out to a redshift z>3. We find a large population of objects of intermediate radio-loudness; there is no evidence in our sample for a bimodal distribution of radio characteristics. The sample includes ~29 broad absorption line quasars, both high and low ionization, and a number of new objects with remarkable optical spectra.

The First Bright QSO Survey

The FIRST Radio Survey provides a new resource for constructing a large quasar sample. With source positions accurate to better than 1\arcsec and a point source sensitivity limit of 1 mJy, it reaches 50 times deeper than previous radio catalogs. We report here on the results of the pilot phase for a FIRST Bright Quasar Survey (FBQS). Based on matching the radio catalog from the initial 300 deg$^2$ of FIRST coverage with the optical catalog from the Automated Plate Machine (APM) digitization of Palomar Sky Survey plates, we have defined a sample of 219 quasar candidates brighter than E = 17.50. We have obtained optical spectroscopy for 151 of these and classified 25 others from the literature, yielding 69 quasars or Seyfert~1 galaxies, of which 51 are new identifications. The brightest new quasar has an E magnitude of 14.6 and z = 0.91; four others are brighter than E = 16. The redshifts range from z=0.12 to 3.42. Half of the detected objects are radio quiet with L$_{\rm 21cm} < 10^{32.5}$ ergs/s. We use the results of this pilot survey to establish criteria for the FBQS that will produce a quasar search program which will be 70\% efficient and 95\% complete to a 21-cm flux density limit of 1.0 mJy.