FIRST Survey Publications
FIRST Survey Publications"Optical Counterparts for 70,000 Radio Sources: APM Identifications for the FIRST Radio Survey,"
McMahon, R.G., Helfand, D.J., White, R.L. and Becker, R.H. 2001, Astrophysical Journal, in press
We describe a program to identify optical counterparts to radio sources from the VLA FIRST survey using the Cambridge APM scans of the POSS-I plates. We use radio observations covering 4150 square degrees of the north Galactic cap to a 20 cm flux density threshold of 1.0 mJy; the 382,892 sources detected all have positional uncertainties of <1" (radius of 90% confidence). Our description of the APM catalog, derived from the 148 POSS-I O and E plates covering this region, includes an assessment of its astrometric and photometric accuracy, a photometric recalibration using the Minnesota APS catalog, a discussion of the classification algorithm, and quantitative tests of the catalog's reliability and completeness. We go on to show how the use of FIRST sources as astrometric standards allows us to improve the absolute astrometry of the POSS plates by nearly an order of magnitude to ~0.15" rms. Matching the radio and optical catalogs yields counterparts for over 70,000 radio sources; we include detailed discussions of the reliability and completeness of these identifications as a function of optical and radio morphology, optical magnitude and color, and radio flux density. An analysis of the problem of radio sources with complex morphologies (e.g., double-lobed radio galaxies) is included. We conclude with a brief discussion of the source classes represented among the radio sources with identified counterparts.
This paper is available in HTML, compressed Postscript, and through the astro-ph e-print archives. There are also a number of data tables available online.
Gregg, M.D., Lacy, M., White, R.L., Glikman, E., Helfand, D.J., Becker, R.H., and Brotherton, M.S. 2001, Astrophysical Journal, in press
In a survey of quasar candidates selected by matching the FIRST and 2MASS catalogs, we have found two extraordinarily red quasars. FIRST J013435.7-093102 is a 1 Jy source at z=2.216 and has B-K > 10, while FIRST J073820.1+275045 is a 2.5 mJy source at z=1.985 with B-K = 8.4. FIRST J073820.1+275045 has strong absorption lines of MgII and CIV in the rest frame of the quasar and is highly polarized in the rest frame ultraviolet, strongly favoring the interpretation that its red spectral energy distribution is caused by dust reddening local to the quasar. FIRST J073820.1+275045 is thus one of the few low radio-luminosity, highly dust-reddened quasars known. The available observational evidence for FIRST J013435.7-093102 leads us to conclude that it too is reddened by dust. We show that FIRST J013435.7-093102 is gravitationally lensed, increasing the number of known lensed, extremely dust-reddened quasars to at least three, including MG0414-0534 and PKS1830-211. We discuss the implications of whether these objects are reddened by dust in the host or lensing galaxies. If reddened by their local environment, then we estimate that between 10 and 20% of the radio-loud quasar population is reddened by dust in the host galaxy. The discovery of FIRST J073820.1+275045 and objects now emerging from X-ray surveys suggests the existence of an analogous radio-quiet red quasar population. Such objects will be entirely missed by standard radio or optical quasar surveys. If dust in the lensing galaxies is primarily responsible for the extreme redness of the lensed quasars, then an untold number of gravitationally lensed quasars are being overlooked.
This paper is available through the astro-ph e-print archives.
"The FIRST Bright Quasar Survey III. The South Galactic Cap"
Becker, R. H., White, R. L., Gregg, M. D., Laurent-Muehleisen, S. A., Brotherton, M. S., Impey, C. D., Chaffee, F. H., Richards, G. T., Helfand, D. J., Lacy, M., Courbin, F., and Proctor, D. D. 2001, Astrophysical Journal Supplement 135, 227
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 square degrees 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 four for quasars with a radio-loudness parameter R* > 100.
This paper is available through the astro-ph e-print archives. The figures with spectra in the astro-ph version are low-resolution; there is also a full-resolution gzipped postscript version of the paper available (1.6 Mbytes).
"The First Observations of the Second Brightest Quasar"
Leighly, K.M., Halpern, J.P., Helfand, D.J., Becker, R.H., and Impey, C.D. 2001, Astronomical Journal, in press
We report the discovery of a new bright quasar PHL 1811 as part of a followup program to identify bright quasars in the FIRST radio survey. With B=13.9, R=13.9, and z=0.192, this quasar is now the second brightest quasar (in apparent magnitude) known beyond z=0.1. Optically classified as a Narrow-line Seyfert 1 galaxy (NLS1), PHL 1811 is unusual for an object in this class in that it was not detected in X-rays in the ROSAT All Sky survey or in any previous X-ray survey. A follow-up BeppoSAX observation confirms that it is deficient in X-rays compared with other quasars, but poor signal to noise prevents a definitive characterization of the X-ray spectrum. We consider three alternative hypotheses to explain why PHL 1811 is a weak X-ray source: (1) it is a BALQSO and suffers X-ray absorption; (2) like several other luminous NLS1s, it exhibits high amplitude X-ray variability, and has been observed only when it is in an X-ray quiescent state; (3) it is intrinsically weak because it simply lacks an X-ray emitting region.
This paper is available through the astro-ph e-print archives.
Lacy, M., Laurent-Muehleisen, S. A., Ridgway, S. E., Becker, R. H., and White, R. L. 2001, Astrophysical Journal Letters 551, L17
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 H-beta 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 Mbh1.9+/-0.2(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.
This paper is available through ADS.
"The Gravitational Lens Candidate FBQ 1633+3134"
Morgan, N. D., Becker, R. H., Gregg, M. D., Schechter, P. L., & White, R. L. 2001, Astronomical Journal 121, 611
We present our ground-based optical imaging, spectral analysis, and high-resolution radio mapping of the gravitational lens candidate FBQ 1633+3134. This z=1.52, B=17.7 quasar appears double on CCD images with an image separation of 0.66" and a relatively constant flux ratio of ~3:1 across B, V, R, and I filters. A single 0.27 mJy radio source is detected at 8.46 GHz, coincident within an arcsecond of both optical components, but no companion at radio wavelengths is detected for the system down to a flux level of 0.1 mJy (3 sigma). Spectral observations reveal a rich metal-line absorption system consisting of a strong Mg II doublet and associated Fe I and Fe II absorption features, all at an intervening redshift of z=0.684, suggestive of a lensing galaxy. Point-spread function subtraction of ground-based images however shows no obvious signs of a third object between the two quasar images and places a detection limit of I>~23.0 if such an object exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot be ruled out, the evidence presented here is consistent with FBQ 1633+3134 being a single quasar lensed by a faint, metal-rich galaxy.
This paper is available through ADS.
"Keck HIRES Observations of the QSO FIRST J104459.6+365605: Evidence for a Large-Scale Outflow"
de Kool, M., Arav, N., Becker, R. H., Gregg, M. D., White, R. L., Laurent-Muehleisen, S. A., Price, T., and Korista, K. T. 2001, Astrophysical Journal 548, 609
This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J104459.6+365605, covering the rest wavelength range from 2260 to 2900 A. The line of sight toward the QSO contains two clusters of outflowing clouds that give rise to broad blue-shifted absorption lines. The outflow velocities of the clouds range from -200 to -1200 km s-1 and from -3400 to -5200 km s-1, respectively. The width of the individual absorption lines ranges from 50 to more than 1000 km s-1. The most prominent absorption lines are those of Mg II, Mg I, and Fe II, and Mn II is also present. The low-ionization absorption lines occur at the same velocities as the most saturated Mg II lines, showing that the Fe II, Mg I, and Mg II line-forming regions must be closely associated. Many absorption lines from excited states of Fe II are present, allowing a determination of the population of several low-lying energy levels. The populations of the excited levels are found to be considerably smaller than expected for LTE and imply an electron density in the Fe II line-forming regions of ne~4x103 cm-3. Modeling the ionization state of the absorbing gas with this value of the electron density as a constraint, we find that the distance between the Fe II and Mg I line-forming region and the continuum source is ~700 pc. From the correspondence in velocity between the Fe II, Mg I, and Mg II lines we infer that the Mg II lines must be formed at the same distance. The Mg II absorption fulfills the criteria for broad absorption lines defined by Weymann and coworkers. Therefore, the distance we find between the Mg II line-forming region and the continuum source is surprising, since BALs are generally thought to be formed in outflows at a much smaller distance from the nucleus.
This paper is available through ADS.
Brotherton, M.S., Arav, N., Becker, R.H., Tran, H.D., Gregg, M.D., White, R.L., Laurent-Muehleisen, S.A., and Hack, W. 2001, Astrophysical Journal 546, 134
We report the discovery of a bright quasar (E=15.8, z=0.868) associated with the flat spectrum radio source NVSS J235953-124148. This quasar we designate QSO 2359-1241 possesses a rare combination of extreme properties that make it of special interest. These properties include: intrinsic high-velocity outflow seen in absorption for both high and low-ionization species, high optical polarization (about 5%), significant radio emission, and dust reddening. The dereddened absolute magnitude of QSO 2359-1241 places it among the three most optically luminous quasars known at z<1. High-resolution spectroscopy and a detailed analysis of the optical/ultraviolet absorption features will be given in a companion paper (Arav et al 2000).
This paper is available through the astro-ph e-print archives.
"The Intrinsic Absorber in QSO 2359-1241: Keck and HST Observations"
Arav, N., Brotherton, M.S., Becker, R.H., Gregg, M.D., White, R.L., Price, T., and Hack, W.
2001,
Astrophysical Journal 546, 140
We present detailed analyses of the absorption spectrum seen in QSO 2359-1241 (NVSS J235953-124148). Keck
HIRES data reveal absorption from twenty transitions arising from: He I, Mg I, Mg II, Ca II, and Fe II.
HST data show broad absorption lines (BALs) from Al III 1857, C IV 1549, Si IV 1397, and N V 1240.
Absorption from excited Fe II states constrains the temperature of the absorber to 2000K < T < 10,000K and
puts a lower limit of 10^5 cm^{-3} on the electron number density. Saturation diagnostics show that the
real column densities of He I and Fe II can be determined, allowing to derive meaningful constraints on
the ionization equilibrium and abundances in the flow. The ionization parameter is constrained by the
iron, helium and magnesium data to -3.0 < log(U) < -2.5 and the observed column densities can be
reproduced without assuming departure from solar abundances. From comparison of the He I and Fe II
absorption features we infer that the outflow seen in QSO 2359-1241 is not shielded by a hydrogen
ionization front and therefore that the existence of low-ionization species in the outflow (e.g., Mg II,
Al III, Fe II) does not necessitate the existence of such a front. We find that the velocity width of the
absorption systematically increases as a function of ionization and to a lesser extent with abundance.
Complementary analyses of the radio and polarization properties of the object are discussed in a
companion paper (Brotherton et al. 2000).
This paper is available through the astro-ph
e-print archives.
``Composite Spectra from the FIRST Bright Quasar Survey''
Brotherton, M. S., Tran, H. D., Becker, R. H., Gregg, M. D., Laurent-Muehleisen, S. A., & White, R. L. 2001, Astrophysical Journal 546, 775
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.
This paper is available in compressed Postscript and through the astro-ph e-print archives.
Blanton, E.L., Gregg, M.D., Helfand, D.J., Becker, R.H., Leighly, K., & White, R.L. 2001, Astronomical Journal, in press
We present an optical spectroscopic and imaging study of the environments of a complete sample of moderate-redshift, bent-double radio sources. More than half of the forty radio galaxies in the sample are associated with Abell richness class 0 or greater clusters at z<0.4. Most of the remaining objects are associated with groups, although a few appear to be hosted by nearly isolated elliptical galaxies. For the bent doubles appearing in poor environments, either dense gas must be associated with the systems to provide the ram pressure to bend the lobes, or alternative bending mechanisms will have to be invoked to explain the radio morphologies. Correlation with the ROSAT All Sky Survey Bright and Faint Source Catalogs reveals the majority of the z<0.2 objects in our sample that we classify optically as clusters are also X-ray sources.
This paper is available through the astro-ph e-print archives.
"Long-Term Optical Variability of Radio-Selected Quasars from the FIRST Survey"
Helfand, D.J., Stone, R., Willman, B., White, R.L., Becker, R.H., Price, T., Gregg, M.D., and McMahon, R.G. 2001, Astronomical Journal 121, 1872
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.
This paper is available through the astro-ph e-print archives.
"Effect of Correlated Noise on Source Shape Parameters and Weak Lensing Measurements"
Refregier, A., and Brown, S.T. 2001, Astrophysical Journal, in press
The measurement of shape parameters of sources in astronomical images is usually performed by assuming that the underlying noise is uncorrelated. Spatial noise correlation is however present in practice due to various observational effects and can affect source shape parameters. This effect is particularly important for measurements of weak gravitational lensing, for which the sought image distortions are typically of the order of only 1%. We compute the effect of correlated noise on two-dimensional gaussian fits in full generality. The noise properties are naturally quantified by the noise autocorrelation function (ACF), which is easily measured in practice. We compute the resulting bias on the mean, variance and covariance of the source parameters, and the induced correlation between the shapes of neighboring sources. We show that these biases are of second order in the inverse signal-to-noise ratio of the source, and could thus be overlooked if bright stars are used to monitor systematic distortions. Radio interferometric surveys are particularly prone to this effect because of the long-range pixel correlations produced by the Fourier inversion involved in their image construction. As a concrete application, we consider the search for weak lensing by large-scale structure with the FIRST radio survey. We measure the noise ACF for a FIRST coadded field, and compute the resulting ellipticity correlation function induced by the noise. In comparison with the weak-lensing signal expected in CDM models, the noise correlation effect is important on small angular scales, but is negligible for source separations greater than about 1 arcmin. We also discuss how noise correlation can affect weak-lensing studies with optical surveys.
This paper is available through the astro-ph e-print archives.
"Red Quasars and Quasar Evolution: the Case of BALQSO FIRST J155633.8+351758"
J. Najita, A. Dey, and M. Brotherton, 2000 Astronomical Journal 120, 2859
We present the first near-IR spectroscopy of the z=1.5 radio-loud BALQSO FIRST J155633.8+351758. Both the Balmer decrement and the slope of the rest-frame UV-optical continuum independently suggest a modest amount of extinction along the line of sight to the BLR (E(B-V)~0.5 for SMC-type screen extinction at the QSO redshift). The implied gas column density along the line of sight is much less than is implied by the weak X-ray flux of the object, suggesting that either the BLR and BAL region have a low dust-to-gas ratio, or that the rest-frame optical light encounters significantly lower mean column density lines of sight than the X-ray emission. From the rest-frame UV-optical spectrum, we are able to constrain the stellar mass content of the system. Comparing the maximal stellar mass with the black hole mass estimated from the bolometric luminosity of the QSO, we find that the ratio of the black hole to stellar mass may be comparable to the Magorrian value, which would imply that the Magorrian relation is already in place at z=1.5. However, multiple factors favor a much larger black hole to stellar mass ratio. This would imply that if the Magorrian relation characterizes the late history of QSOs, and the situation observed for F1556+3517 is typical of the early evolutionary history of QSOs, central black hole masses develop more rapidly than bulge masses.
This paper is available through the astro-ph e-print archives.
"Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey"
Gregg, M.D., Becker, R.H., Brotherton, M.S., Laurent-Muehleisen, S.A., Lacy, M., and White, R.L. 2000, Astrophysical Journal 544, 142
We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical spectrum shows unambiguous broad absorption features while its double-lobed radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type II radio source. Its radio luminosity places it at the extreme of the recently established class of radio-loud broad absorption line quasars (Becker et al. 1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate that FIRST J101614.3+520916 is a typical FR-II quasar which has been rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be estimated from its radio structure and optical brightness, indicating that we are viewing the system at a viewing angle of > 40 degrees. The position angles of the radio jet and optical polarization are not well-aligned, differing by 20 to 30 degrees. When combined with the evidence presented by Becker et al. (2000) for a sample of 29 BAL quasars showing that at least some BAL quasars are viewed along the jet axis, the implication is that no preferred viewing orientation is necessary to observe BAL systems in a quasar's spectrum. This, and the probable young nature of compact steep spectrum sources, leads naturally to the alternate hypothesis that BALs are an early stage in the lives of quasars.
This paper is available through the astro-ph e-print archives."A Close Separation Double Quasar Lensed by a Gas-Rich Galaxy"
Gregg, M.D., Wisotzki, L., Becker, R.H., Maza, J., Schechter, P.L., White, R.L., Brotherton, M.S., and Winn, J.N. 2000, astro-ph/0002333
In the course of a Cycle 8 snapshot survey, we have discovered that the z=1.565 quasar HE 0512-3329 is a double with image separation 0.644", almost certainly due to gravitational lensing. The two components differ in brightness by only 0.4 magnitudes and a high signal-to-noise ground-based composite optical spectrum shows no trace of any stellar features at zero redshift, essentially ruling out the possibility that one of the two components is an ordinary Galactic star. The optical spectrum shows strong absorption features of MgII, MgI, FeII, FeI, and CaI, all at an identical intervening redshift of z=0.9313, probably due to the lensing object. The strength of the MgII and the presence of the other low ionization absorption features is strong evidence for a damped Lyman alpha system, likely the disk of a spiral galaxy. Point spread function fitting to remove the two quasar components from the STIS image leads to a tentative detection of a third object which may be the nucleus of the lensing galaxy. The brighter component is significantly redder than the fainter, due to either differential extinction or microlensing.
This paper is available through the astro-ph e-print archives.
Becker, R.H., White, and Arav, N., 2000, Astrophysical Journal, 538, 72
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 2, 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 to be inconsistent with simple unified models in which BAL quasars constitute a subset of quasars seen edge-on.
This paper is available through ADS.
Brinkmann, W., Laurent-Muehleisen, S.A., Voges, W., Siebert, J., Becker, R.H., Brotherton, M.S., White, R.L., and Gregg, M.D. 2000, Astronomy & Astrophysics, 356, 445
We present the results of a correlation of the ROSAT All-Sky Survey with the April 1997 release of the VLA 20cm FIRST catalogue. We focus our analysis on the 843 X-ray sources which have unique radio counterparts. The majority of these objects (84%) have optical counterparts on the POSS 1 plates. Approximately 30% have been previously classified and we obtain new spectroscopic classifications for 85 sources by comparison with the ongoing FIRST Bright Quasar Survey and 106 additional sources from our own new spectroscopic data. Approximately 51% of the sources are presently classified, and the majority of the unclassified objects are optically faint. The newly classified sources are generally radio weak, exhibiting properties intermediate with previous samples of radio- and X-ray-selected AGN. This also holds for the subsample of 71 BL Lacs which includes many intermediate objects. The 146 quasars show no evidence for a bimodal distribution in their radio-loudness parameter, indicating that the supposed division between radio-quiet and radio-loud AGN may not be real. The X-ray and radio luminosities are correlated over two decades in radio luminosity, spanning the radio-loud and radio-quiet regimes, with radio-quiet quasars showing a linear correlation between the two luminosities. Many of the sources show peculiar or unusual properties which call for more detailed follow-up observations. We also give the X-ray and radio data for the 518 X-ray sources for which more than one radio object is found. Because of the difficulties inherent in identifying optical counterparts to these complex sources, we do not consider these data in the current analysis.
The tables are available in electronic form at the CDS via anonymous ftp from 130.79.128.5
This paper is available through ADS.
``The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later''
White, R. L., Becker, R. H., Gregg, M. D., Laurent-Muehleisen, S. A., & Brotherton, M. S., Impey, C. D., Petry, C. E., Foltz, C. B., Chaffee, F. H., Richards, G. T., Oegerle, W. R., Helfand, D. J. McMahon, R. G., & Cabanela, J. E. 2000, Astrophysical Journal (Supplement), 126, 133
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.
This paper is available in compressed Postscript and through the astro-ph e-print archives.
"FIRST Bent Double Radio Sources: Tracers of High-Redshift Clusters"
Blanton, E.L., Gregg, M.D., Helfand, D.J., Becker, R.H., and White, R.L 2000, Astrophysical Journal, 531, 118
Bent-double radio sources can act as tracers for clusters of galaxies. We present imaging and
spectroscopic observations of the environments surrounding 10 of these sources (most of them wide-angle
tails [WATs]) selected from the VLA FIRST survey. Our results reveal a previously unknown cluster
associated with eight of the radio sources with redshifts in the range 0.33 This paper is available through
ADS.
"ROSAT HRI Observations of Radio-Loud AGN"
Gliozzi, M., Brinkmann, W., Laurent-Muehleisen, S. A., Takalo, L. O., & Sillanpaa, A., 1999,
Astronomy & Astrophysics, 352, 437
We present the results of three ROSAT HRI observations of AGN expected to reside in clusters of galaxies.
Although the exposures were truncated by the premature end of the ROSAT mission, valuable information
could be achieved which greatly improved upon the previous PSPC results.
For RGB 1745+398 we could separate the cluster emission from that of the BL Lac and could confirm the
cluster parameters obtained from optical follow-up observations. In MRC 0625-536 the flux from the central
point source contributes less than 3% to the total X-ray flux and the eastern component of the dumbbell
galaxy seems to be the X-ray emitter. RXJ1234.6+2350 appears to be extended in X-rays. The X-ray flux is
centered on a quasar, but optical spectroscopy indicates that the nearby radio galaxies reside in a
previously unknown cluster at redshift z$sigma im$0.134.
This paper is available through
ADS.
"What Determines the Depth of Broad Absorption Lines? Keck HIRES Observations of BALQSO
1603+3002"
N. Arav, R.H. Becker, S.A. Laurent-Muehleisen, M.D. Gregg, R.L. White, and M. de Kool
1999
Astrophysical Journal, 524, 566
We find that the depth and shape of the broad absorption lines (BALs) in BALQSO 1603+3002 are determined
largely by the fraction of the emitting source which is covered by the BAL flow. In addition, the observed
depth of the BALs is poorly correlated with their real optical depth. The implication of this result is
that abundance studies based on direct extraction of column densities from the depth of the absorption
troughs are unreliable. Our conclusion is based on analysis of unblended absorption features of two lines
from the same ion (in this case the Si IV doublet), which allows unambiguous separation of covering factor
and optical depth effects. The complex morphology of the covering factor as a function of velocity
suggests that the BALs are produced by several physically separated outflows. The covering factor is ion
dependent in both depth and velocity width. We also find evidence that in BALQSO 1603+3002 the flow does
not cover the broad emission line region.
This paper is available through
ADS.
"Discovery of a Radio-loud/Radio-quiet Binary Quasar"
M.S. Brotherton, M.D. Gregg, R.H. Becker, S.A. Laurent-Muehleisen, R.L. White, and S.A. Stanford
1999
Astrophysical Journal (Letters), 514, L61
We report the discovery of a small-separation quasar pair (z=0.586, O=18.4, 19.2, and a separation of
2.3") associated with the radio source FIRST J164311.3+315618 (S_1400=120 mJy). The spectrum of the
brighter quasar (A) has a much stronger narrow emission line spectrum than the other (B), and it also has
stronger Balmer lines relative to the continuum. The continuum ratio of the spectra is flat in the blue
(lambda_obs<6000 E) at about 2.1 but falls to 1.5 at longer wavelengths. A K^' image shows two unresolved
sources with a flux ratio of 1.3. The different colors appear to result from the contribution of the host
galaxy of B, which is evident from Ca II and high-order Balmer absorption lines that are indicative of a
substantial young stellar population. New 3.6 cm VLA observations show that the compact radio source is
coincident with quasar A (B is only marginally detected). We rule out the lensing hypothesis because the
optical flux ratio is A/B~1.5-2, while the radio flux ratio is A/B>~40, and conclude that this system is a
binary. Moreover, the radio-loud quasar is a compact, steep spectrum source. FIRST J164311.3+315618A, B is
the lowest redshift and smallest separation binary quasar yet identified.
This paper is available through
ADS.
"The FIRST Unbiased Survey for Radio Stars"
D.J. Helfand, S. Schnee, R.H. Becker, R.L. White, and R.G. McMahon
1999,
Astronomical Journal 117, 1568
Comparison of the VLA FIRST survey with various catalogs of bright stars allows an examination of the
prevalence of stellar radio emission independent of optical selection criteria. This FIRST unbiased survey
for radio stars covers nearly 5000 deg^2 of the northern sky to a flux density limit of 0.7 mJy at 20 cm.
Using astrometric catalogs that include proper-motion information, we have detected 26 stellar radio
sources, doubling the number of such objects previously known in this region of high-latitude sky. We also
show that, in the absence of good proper motions, even the 1" precision of the FIRST positions is
insufficient to avoid crippling chance coincidence rates. We calculate the fraction of radio detections as
a function of stellar magnitude and show that, when proper motions from the Guide Star Catalog II become
available, the number of stellar radio source detections should increase fourfold.
This paper is available through
ADS.
"Discovery of Radio-Loud Broad Absorption Line Quasars Using Ultraviolet Excess and Deep Radio
Selection"
Brotherton, M.S., Van Breugel, W., Smith, R.J., Boyle, B.J., Shanks, T. Croom, S.M., Miller, L., and
Becker, R.H.
1998,
Astrophysical Journal 505, L7
We report the discovery of five broad absorption line (BAL) QSOs in a complete sample of 111 ultraviolet
excess (UVX) QSO candidates also detected in the NRAO VLA Sky Survey. All five BAL QSOs, which include two
high-ionization BAL QSOs and three low-ionization BAL QSOs, are formally radio loud. Of QSOs with z>0.4 ,
3%+/-2% show low-ionization BALs, and of QSOs with z>1.5 , all radio loud, 9%+/-5% show BALs; these
frequencies are consistent with those of optical surveys. While the first reported radio-loud BAL QSO,
FIRST J155633.8+351758, is likely to be heavily dust reddened and thus less radio loud than indicated by
its observed radio-to-optical luminosity, these QSOs are UVX-selected and probably free of significant
dust along the line of sight. We point out unusual features in two of the BAL QSOs and discuss the
significance finding these heretofore rare objects.
This paper is available through
ADS.
"Theory and Statistics of Weak Lensing from Large-Scale Structure Mass Inhomogeneities"
Kamionkowski, M., Babul, A., Cress, C.M., and Refregier, A.
1998,
Monthly Notices of the Royal Astronomical Society 301, 1064
Weak lensing by large-scale mass inhomogeneities in the Universe induces correlations in the observed
ellipticities of distant sources. We first review the harmonic analysis and statistics required of these
correlations and discuss calculations for the predicted signal. We consider the ellipticity correlation
function, the mean-square ellipticity, the ellipticity power spectrum and a global maximum-likelihood
analysis to isolate a weak-lensing signal from the data. Estimates for the sensitivity of a survey of a
given area, surface density, and mean intrinsic source ellipticity are presented. We then apply our
results to the FIRST radio-source survey. We predict an rms ellipticity of roughly 0.011 in 1x1 deg^2
pixels and 0.018 in 20x20 arcmin^2 pixels if the power spectrum is normalized to sigma_8Omega^0.53=0.6, as
indicated by the cluster abundance. The signal is significantly larger in some models if the power
spectrum is normalized instead to the COBE anisotropy. The uncertainty in the predictions from imprecise
knowledge of the FIRST redshift distribution is about 25 per cent in the rms ellipticity. We show that
FIRST should be able to make a statistically significant detection of a weak-lensing signal for
cluster-abundance-normalized power spectra.
This paper is available through
ADS.
"A Search for High-redshift Quasars Among GB/FIRST Flat-spectrum Radio Sources"
Hook, I.M., Becker, R.H., McMahon, R.G. and White, R.L.
1998,
Monthly Notices of the Royal Astronomical Society 97, 1115
We present the method and first results of a survey for high-redshift (z>3) radio-loud quasars, which is
based on optical identifications of 2902 flat-spectrum radio sources with S_5GHz>=25 mJy. The radio sample
was defined over a 1600 deg^2 region using the 5-GHz Green Bank survey and the 1.4-GHz VLA FIRST survey.
560 sources were identified to a limit of E = 19.5 on APM scans of POSS-I plates, and 337 of these optical
counterparts are unresolved. From these a complete sample of 73 sources for spectroscopic follow-up was
defined based on criteria of red (O-E>=1.2) optical colour. We have obtained spectra for 36 of these, and
an additional 14 have redshifts in the literature, thus 70 per cent of the spectroscopic sample is
completed. Six objects in the sample were found to be radio-loud quasars with z>3, of which two were
previously known. The efficiency of the spectroscopic phase of the survey is therefore about 1 in 9,
whereas without the colour selection criterion the efficiency would have been 1 in sim40. The six z>3
quasars were found in an effective area of 1100 deg^2, implying a surface density of one flat-spectrum z>3
radio-loud quasar per 190 deg^2 to limits of E = 19.5 and S_5GHz>=25mJy. This survey has also produced the
first known radio-loud BAL quasar, 1556+3517 with z=1.48, which has been reported in an earlier paper.
This object has a redder optical colour (O-E=2.56) than all the z>3 quasars found in this survey to date.
In addition, we have obtained spectra of 22 GB/FIRST sources that are not part of the complete sample. We
give positions, E (red) magnitudes, O-E colours, radio fluxes, radio spectral indices and redshifts where
possible for objects for which we have obtained spectra. We give spectra and finding charts for the z>3
quasars.
This paper is available through
ADS.
"The First FIRST Gravitationally Lensed Quasar: FBQ 0951+2635"
Schechter, P., Gregg, M.D., Becker, R.H., Helfand, D.J., and White, R.L.
1998,
Astrophysical Journal, 115, 1371
The V=16.9 quasar FBQ 0951+2635 at redshift z=1.24 appears double on CCD exposures taken in subarcsecond
seeing. The two objects are separated by 1.1" and differ in brightness by 0.9 mag. VLA observations show
the radio source to be double with the same separation and position angle. Spectra
taken with the Keck II telescope show the two components to have nearly identical emission line spectra,
but with somewhat different absorption line systems. Subtraction of two stellar point spread functions
from the pair of components consistently leaves a residual object. Depending upon whether this third
object is extended or a point source it may be as much as 1/10 or as little as 1/100 as bright as the
brighter QSO component. The observations leave no doubt that the 2 brighter objects are gravitationally
lensed images of the same quasar. The third object might be either the lensing galaxy or a third image of
the quasar, but both interpretations have serious shortcomings.
"Constraining Omega0 with the Angular-Size Redshift Relation of Double-Lobed Quasars in the
FIRSTSurvey"
Buchalter, Y., Helfand, D.J., Becker, R.H., and White, R.L. 1998,
Astrophysical Journal, 494, 503
In previous attempts to measure cosmological parameters from the angular size-redshift ( theta -z)
relation of double-lobed radio sources, the observed data have generally been consistent with a static
Euclidean universe rather than with standard Friedmann models, and past authors have disagreed
significantly as to what effects are responsible for this observation. These results and different
interpretations may be due largely to a variety of selection effects and differences in the sample
definitions destroying the integrity of the data sets, and inconsistencies in the analysis undermining the
results. Using the VLA FIRST survey, we investigate the theta -z relation for a new sample of double-lobed
quasars. We define a set of 103 sources, carefully addressing the various potential problems that, we
believe, have compromised past work, including a robust definition of size and the completeness and
homogeneity of the sample, and further devise a self-consistent method to assure accurate morphological
classification and account for finite resolution effects in the analysis. Before focusing on cosmological
constraints, we investigate the possible impact of correlations among the intrinsic properties of these
sources over the entire assumed range of allowed cosmological parameter values. For all cases, we find
apparent size evolution of the form l ~ (1 + z)c, with c ~ -0.8 +/- 0.4, which is found to arise mainly
from a power-size correlation of the form l ~ P beta ( beta ~ - 0.13 +/- 0.06) coupled with a
power-redshift correlation. Intrinsic size evolution is consistent with zero. We also find that in all
cases, a subsample with c ~ 0 can be defined, whose theta -z relation should therefore arise primarily
from cosmological effects. These results are found to be independent of orientation effects, although
other evidence indicates that orientation effects are present and consistent with predictions of the
unified scheme for radio-loud active galactic nuclei. The above results are all confirmed by nonparametric
analysis. Contrary to past work, we find that the observed theta -z relation for our sample is more
consistent with standard Friedmann models than with a static Euclidean universe. Though the current data
cannot distinguish with high significance between various Friedmann models, significant constraints on the
cosmological parameters within a given model are obtained. In particular, we find that a flat,
matter-dominated universe ( Omega0 = 1), a flat universe with a cosmological constant, and an open
universe all provide comparably good fits to the data, with the latter two models both yielding Omega0 ~
0.35 with 1 sigma ranges including values between ~0.25 and 1.0; the c ~ 0 subsamples yield values of
Omega0 near unity in these models, though with even greater error ranges. We also examine the values of
H0 implied by the data, using plausible assumptions about the intrinsic source sizes, and find these to be
consistent with the currently accepted range of values. We determine the sample size needed to improve
significantly the results and outline future strategies for such work.
This paper is available through
ADS.
"Interpreting the Clustering of Radio Sources"
Cress, C.M. and Kamionkowski, M.
1998,
Monthly Notices of the Royal Astronomical Society, 97, 486
We develop the formalism required to interpret, within a CDM framework, the angular clustering of sources
in a deep radio survey. The effect of non-linear evolution of density perturbations is discussed, as is
the effect of the assumed redshift distribution of sources. We also investigate what redshift ranges
contribute to the clustering signal at different angular scales. Application of the formalism is focused
on the clustering detected in the FIRST survey, but measurements made for other radio surveys are also
investigated. We comment on the implications for the evolution of clustering.
This paper is available through
ADS.
"The FIRST Radio-Loud Broad Absorption Line QSO and Evidence for
a Hidden Population of Quasars''
Becker, R. H.,
Gregg, M. D.,
Hook, I. M.,
McMahon, R. G.,
White, R. L. &
Helfand, D. J.
1997,
Astrophysical Journal (Letters), 479, L93
We have discovered two low-ionization broad absorption line quasars in
programs to obtain optical spectra for radio-selected quasar
candidates from the VLA FIRST Survey.
Both belong to the extremely rare class of BAL QSOs that exhibit
narrow absorption lines from metastable excited levels of Fe II and
Fe III. Until now, there was just a single object in this class,
0059-2735 (Hazard et al. 1987). In addition, one of our new objects
is the first known radio-loud BAL QSO. The properties of these
three unusual objects suggest a trend of increasing radio luminosity
with the amount of absorption to the quasar, and are perhaps
transition objects between radio-loud and radio-quiet quasars.
The two new objects are from a radio-selected sample comprising less
than 200 quasars; one is heavily attenuated at optical wavelengths in
the observed frame. These objects would be easily overlooked by most
optical QSO searches; their abundance in the radio sample suggests
that they may be representatives of a largely undetected component of
the quasar population, perhaps as numerous as ordinary low-ionization
BAL QSOs which constitute 1-2% of all QSOs.
This paper is available in
HTML,
compressed Postscript,
and through the
astro-ph
e-print archives.
``A Catalog of 1.4 GHz Radio Sources from the FIRST Survey''
White, R. L., Becker, R. H., Helfand, D. J., & Gregg, M. D. 1997,
Astrophysical Journal, 475, 479
Describes the construction of the FIRST survey catalog. An extensive
set of tests have been carried out to determine the accuracy of the
catalog parameters. The source flux density distribution dN/dS
is determined, and the FIRST catalog is compared with the Guide Star
Catalog, the IRAS Faint Source Catalog, and the ROSAT WGA catalog.
This paper is available in
HTML and
compressed Postscript.
``The Angular Two-Point Correlation Function for the FIRST Radio
Survey''
Cress, C. M.,
Helfand, D. J.,
Becker, R. H.,
Gregg, M. D., &
White, R. L.
1996,
Astrophysical Journal, 473, 7
We have used the FIRST catalog to obtain the first high-significance
measurement of the two-point angular correlation for a deep radio
sample. We find that the correlation function between 0.02° and
2° is well fitted by a power law of the form A theta^gamma where
A=3x10^-3 and gamma=-1.1. On small scales (theta<0.2°),
double and multi-component sources are shown to have a larger
clustering amplitude than that of the whole sample. Sources with flux
densities below 2 mJy are found to have a shallower slope than that
obtained for the whole sample, consistent with there being a
significant contribution from starbursting galaxies at these faint
fluxes. The cross-correlation of radio sources and Abell clusters is
determined. A preliminary approach to inferring spatial information is
outlined.
This paper is available in
HTML,
compressed Postscript,
and through the
astro-ph
e-print archives.
``The FIRST Bright QSO Survey''
Gregg, M. D. Becker, R. H., White, R. L., Helfand, D. J., McMahon, R.
G., & Hook, I. M. 1996, Astronomical Journal, 112, 407
Describes spectroscopic followup observations of bright
quasar candidates in the FIRST catalog. This paper is
available in HTML,
compressed Postscript, and
through the
astro-ph
e-print archives.
``The FIRST Survey: Faint Images of the Radio Sky at Twenty-cm''
Becker, R. H., White, R. L., & Helfand, D. J. 1995,
Astrophysical Journal, 450, 559
Describes the genesis of
the FIRST project, the survey design, and results of a variety of tests
using the initial observations to ensure that we are achieving our
scientific and technical goals. This paper is also available in both
HTML and
compressed Postscript. The
postscript version is in the paper's final published form, while the
HTML version differs slightly from the published version.
Becker, R. H., White, R. L., & Helfand, D. J. 1994, Astronomical
Data Analysis Software and Systems III, ASP Conference Series, v.
61, eds. D. R. Crabtree, R. J. Hanisch, & J. Barnes, p. 165
A paper describing the FIRST project, available in either HTML or compressed Postscript.
Home | What's New | Description | Status of Observations | Search
Images | Cutouts | Catalogs | Publications | Acknowledgements
Richard L. White, rlw@stsci.edu
2001 October 18