Urrutia, T., Lacy, M., and Becker, R.H. 2008, Astrophysical Journal, 674, 8
We present Hubble Space Telescope ACS images of 13 dust-reddened type 1 quasars selected from the FIRST/2MASS Red Quasar Survey. These quasars have high intrinsic luminosities after correction for dust obscuration (-23.5>=MB>=-26.2 from K-magnitude). The images show strong evidence of recent or ongoing interaction in 11 of the 13 cases, even before the quasar nucleus is subtracted. None of the host galaxies are well fit by a simple elliptical profile. The fraction of quasars showing interaction is significantly higher than the 30% seen in samples of host galaxies of normal, unobscured quasars. There is a weak correlation between the amount of dust reddening and the magnitude of interaction in the host galaxy, measured using the Gini coefficient and the concentration index. Although few host galaxy studies of normal quasars are matched to ours in intrinsic quasar luminosity, no evidence has been found for a strong dependence of merger activity on host luminosity in samples of the host galaxies of normal quasars. We thus believe that the high merger fraction in our sample is related to their obscured nature, with a significant amount of reddening occurring in the host galaxy. The red quasar phenomenon seems to have an evolutionary explanation, with the young quasar spending the early part of its lifetime enshrouded in an interacting galaxy. This might be further indication of a link between AGNs and starburst galaxies.
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Glikman, E., Helfand, D.J., White, R.L., Becker, R.H., Gregg, M.D., and Lacy, M. 2007, Astrophysical Journal, 667, 673
Combining radio observations with optical and infrared color selection, demonstrated in our pilot study to be an efficient selection algorithm for finding red quasars, we have obtained optical and infrared spectroscopy for 120 objects in a complete sample of 156 candidates from a sky area of 2716 deg2. Consistent with our initial results, we find that our selection criteria (J-K>1.7, R-K>4.0) yield a ~50% success rate for discovering quasars substantially redder than those found in optical surveys. Comparison with UVX- and optical color-selected samples shows that >~10% of the quasars are missed in a magnitude-limited survey. Simultaneous two-frequency radio observations for part of the sample indicate that a synchrotron continuum component is ruled out as a significant contributor to reddening the quasars' spectra. We go on to estimate extinctions for our objects assuming that their red colors are caused by dust. Continuum fits and Balmer decrements suggest E(B-V) values ranging from near zero to 2.5 mag. Correcting the K-band magnitudes for these extinctions, we find that for K<=14.0, red quasars make up between 25% and 60% of the underlying quasar population; owing to the incompleteness of 2MASS at fainter K-band magnitudes, we can only set a lower limit to the radio-detected red quasar population of >20%-30%.
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Croft, S., de Vries, W., and Becker, R.H. 2007, Astrophysical Journal Letters, 667, L13
We correlate the positions of 13,240 brightest cluster galaxies (BCGs) with 0.1<=z<=0.3 from the maxBCG catalog with radio sources from the FIRST survey to study the sizes and distributions of radio AGNs in galaxy clusters. We find that 19.7% of our BCGs are associated with FIRST sources, and this fraction depends on the stellar mass of the BCG, and to a lesser extent on the richness of the parent cluster (in the sense of increasing radio-loudness with increasing mass). The intrinsic size of the radio emission associated with the BCGs peaks at 55 kpc, with a tail extending to 200 kpc. The radio power of the extended sources places them on the divide between FR I and FR II type sources, while sources compact in the radio tend to be somewhat less radio-luminous. We also detect an excess of radio sources associated with the cluster, instead of with the BCG itself, extending out to ~1.4 Mpc.
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de Vries, W.H., Hodge, J.A., Becker, R.H., White, R.L., and Helfand, D.J. 2007, Astronomical Journal, 134, 457
We investigate faint radio emission from low- to high-luminosity active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey. Their radio properties are inferred by co-adding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [O III] luminosity, emission-line ratios, and the strength of the 4000 break. We detect a strong trend for sources that are actively undergoing star formation to have excess radio emission beyond the ~1028 ergs s-1 Hz-1 level found for sources without any discernible star formation. Furthermore, this additional radio emission correlates well with the strength of the 4000 break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission-line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star formation vs. AGNs). For both cases we find a strong, almost identical correlation between [O III] and radio luminosity, with the AGN sample extending toward lower, and the star formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion sigma of the host galaxy. For systems at similar redshifts and values of sigma, the star formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.
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White, R.L., Helfand, D.J., Becker, R.H., Glikman, E., and de Vries, W. 2007, Astrophysical Journal, 654, 99
We present a technique to explore the radio sky into the nanojansky regime by employing image stacking using the FIRST survey. We first discuss the nonintuitive relationship between the mean and median values of a non-Gaussian distribution that is dominated by noise, followed by an analysis of the systematic effects present in FIRST's 20 cm VLA snapshot images. Image stacking allows us to recover the properties of source populations with flux densities a factor of 30 or more below the rms noise level. Mean estimates of radio flux density, luminosity, etc. are derivable for any source class having arcsecond positional accuracy. We use this technique to compute the mean radio properties for 41,295 quasars from the SDSS DR3 catalog. There is a tight correlation between optical and radio luminosity, with the radio luminosity increasing as the 0.85 power of optical luminosity. This implies declining radio loudness with optical luminosity: the most luminous objects (MUV=-28.5) have average radio-to-optical ratios 3 times lower than the least luminous objects (MUV=-20). There is also a striking correlation between optical color and radio loudness: quasars that are either redder or bluer than the norm are brighter radio sources, with objects 0.8 mag redder than the SDSS composite spectrum having radio loudness ratios that are higher by a factor of 10. We explore the long-standing question of whether a radio-loud/radio-quiet dichotomy exists in quasars, finding that optical selection effects probably dominate the distribution function of radio loudness, which has at most a modest (~20%) inflection between the radio-loud and radio-quiet ends of the distribution. We also find, surprisingly, that broad absorption line quasars have higher mean radio flux densities, with the greatest disparity arising in the rare low-ionization BAL subclass.
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McGreer, I.D., Becker, R.H., Helfand, D.J., and White, R.L. 2006, Astrophysical Journal, 652, 157
From examination of only 4 deg2 of sky in the NOAO Deep Wide-Field Survey (NDWFS) region, we have identified the first radio-loud quasar at a redshift z>6. The object, FIRST J1427385+331241, was discovered by matching the FLAMINGOS Extragalactic Survey (FLAMEX) IR survey to Faint Images of the Radio Sky at Twenty cm (FIRST) survey radio sources with NDWFS counterparts. One candidate z>6 quasar was found, and spectroscopy with the Keck II telescope confirmed its identification yielding a redshift z=6.12. The object is a broad absorption line (BAL) quasar with an optical luminosity of MB~-26.9 and a radio-to-optical flux ratio ~60. Two Mg II absorptions systems are present at redshifts of z=2.18 and z=2.20. We briefly discuss the implications of this discovery for the high-redshift quasar population.
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Schaefer, J.J., Brotherton, M.S., Shang, Z., Gregg, M.D., Becker, R.H., Laurent-Muehleisen, S.A., Lacy, M., and White, R.L. 2006, Astronomical Journal, 132, 1464
We have detected FIRST J101614.3+520916 with the XMM-Newton X-ray observatory. FIRST J101614.3+520916, one of the most extreme radio-loud, broad absorption line (BAL) quasars so far discovered, is also a Fanaroff-Riley type II radio source. We find that, compared to its estimated intrinsic X-ray flux, the observed X-rays are likely suppressed and that the observed hardness ratio indicates significant soft X-ray photons. This is inconsistent with the simplest model, a normal quasar spectrum absorbed by a large neutral H I column density, which would primarily absorb the softer photons. More complex models, involving partial covering, an ionized absorber, ionized mirror reflection, or jet contributions need to be invoked to explain this source. The suppressed but soft X-ray emission in this radio-loud BAL quasar is consistent with the behavior displayed by other BAL quasars, both radio-loud and radio-quiet.
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Gregg, M.D., Becker, R.H., and de Vries, W. 2006, Astrophysical Journal, 641, 210
By combining the Sloan Digitized Sky Survey Third Data Release quasar list with the VLA FIRST survey, we have found five new objects having both broad absorption lines (BALs) 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 two previously known FR II-BAL quasars, J1016+5209 and LBQS 1138-0126, 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 anticorrelation 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 that 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 105 yr, with the combined FR II, high-ionization broad absorption phase being even shorter by another factor of 10 or more.
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Whalen, D.J., Laurent-Muehleisen, S.A., Moran, E.C., and Becker, R.H. 2006, Astronomical Journal, 131, 1948
We present results from the analysis of the optical spectra of 47 radio-selected narrow-line Seyfert 1 (NLS1) galaxies. These objects are a subset of the First Bright Quasar Survey and were initially detected at 20 cm (flux density limit ~1 Jy) 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 ~5.
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de Vries, W.H., Becker, R.H., and White, R.L. 2006, Astronomical Journal, 131, 666
We have combined a sample of 44,984 quasars selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 with the FIRST radio survey. Using a novel technique in which the optical quasar position is matched to the complete radio environment within 450", we are able to characterize the radio morphological makeup of what is essentially an optically selected quasar sample, regardless of whether the quasar (nucleus) itself has been detected in the radio. About 10% of the quasar population has radio cores brighter than 0.75 mJy at 1.4 GHz, and 1.7% have double-lobed FR2-like radio morphologies. About 75% of the FR2 sources have a radio core (>0.75 mJy). A significant fraction (~40%) of the FR2 quasars are bent by more than 10, indicating interactions of the radio plasma with either the intracluster medium or intergalactic medium. We found no evidence for correlations with redshift among our FR2 quasars; radio lobe flux densities and radio source diameters of the quasars have similar distributions at low (mean 0.77) and high (mean 2.09) redshifts. Using a smaller high-reliability FR2 sample of 422 quasars and two comparison samples of radio-quiet and non-FR2 radio-loud quasars matched in their redshift distributions, we constructed composite optical spectra from the SDSS spectroscopic data. Based on these spectra we can conclude that the FR2 quasars have stronger high-ionization emission lines compared to both the radio-quiet and non-FR2 radio-loud sources. This is consistent with the notion that the emission lines are brightened by ongoing shock ionization of ambient gas in the quasar host as the radio source expands.
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Brotherton, M.S., Laurent-Muehleisen, S.A., Becker, R.H., Gregg, M.D., Telis, G., White, R.L., and Shang, Z. 2005, Astronomical Journal, 130, 2006
We report the results of a Chandra X-Ray Observatory survey of five formally radio-loud broad absorption line (BAL) quasars. These five objects include BAL quasars with a range of properties, including both high- and low-ionization BALs. All five BAL quasars are detected in 5 ks ACIS-S exposures, with counts ranging from 12 to 55. The X-ray count rates are down by factors of 40 or more compared to expectations based on the spectral energy distributions of normal, unabsorbed radio-loud quasars; this is the same sort of behavior seen in radio-quiet BAL quasars. Interestingly, the hardness ratios are rather soft and inconsistent with absorption from a neutral hydrogen column density large enough to suppress the X-rays as observed. We conclude that in many cases the X-rays emanating from BAL quasars must be reflected, scattered, or leaked through an ionized absorber or a neutral absorber that does not completely cover the X-ray source (covering >=98%), or that we are seeing an unabsorbed X-ray source perhaps associated with a radio jet. Much higher counts are required to distinguish among these possibilities. We note several suggestive correlations involving X-ray properties that require verification using larger samples. One source, FIRST J1556+3517, appears to be the X-ray brightest low-ionization BAL quasar known, other than the special case of the nearby Mrk 231. The very faint X-ray emission from FIRST J1044+3656 is consistent with significant obscuration, which strongly favors the multiphase X-ray shielding models of this object in the literature.
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Glikman, E., Gregg, M.D., Lacy, M., Helfand, D.J., Becker, R.H., and White, R.L. 2004, Astrophysical Journal, 607, 60
We have constructed a sample of bright near-infrared sources that are detected at radio wavelengths but undetected on the first-generation Palomar Observatory Sky Survey (POSSI) plates in order to search for a population of dust-obscured quasars. Optical and infrared spectroscopic follow-up of the sample has led to the discovery of 17 heavily reddened quasars (B-K>6.5), 14 of which are reported here for the first time. This has allowed us to define a region in the R-K, J-K color plane in which 50% of the radio-selected objects are highly reddened quasars. We compare the surface density of this previously overlooked population to that of ultraviolet-excess radio-selected quasars, finding that they make up ~20% of the total quasar population for K<~15.5.
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de Vries, W.H., Becker, R.H., White, R.L., and Helfand, D.J. 2004, AJ, 127, 2565 , Astronomical Journal, 127, 2565
A sample of 123 radio sources that exhibit significant variations at 1.4 GHz on a 7 year baseline has been created using FIRST VLA B-configuration data from 1995 and 2002 on a strip at Dec=0 near the south Galactic cap. This sample spans the range of radio flux densities from ~2 to 1000 mJy. It presents both in size and radio flux density range a unique starting point for variability studies of galaxies and quasars harboring lower luminosity active galactic nuclei (AGNs). We find, by comparing our variable and nonvariable control samples with the Sloan Digital Sky Survey, the following: (1) The quasar fraction of both the variable and nonvariable samples declines as a function of declining radio flux density levels; (2) our variable sample contains a consistently higher fraction of quasars than the nonvariable control sample, irrespective of radio flux; (3) the variable sources are almost twice as likely to be retrieved from the optical SDSS data than the nonvariable ones; (4) based on relative numbers, we estimate that quasars are about 5 times more likely to harbor a variable radio source than are galaxies; and (5) there does not appear to be any significant optical color offset between the two samples, even though the suggestive trend for sources to be bluer when a variable has been detected before and may be real. This leads us to conclude that both radio variability and radio flux density levels, in combination with accurate optical information, are important discriminators in the study of (radio) variability of galaxies. The latter start to dominate the source counts below ~20 mJy. In any case, variability appears to be an intrinsic property of radio sources and is not limited to quasars. Radio variability at low flux density levels may offer a unique tool in AGN unification studies.
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White, R.L., Helfand, D.J., Becker, R.H., Gregg, M.D., Postman, M., Lauer, T.R., and Oegerle, W. 2003, Astronomical Journal, 126, 706
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, F(20cm)>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. Based on observations obtained with the W. M. Keck Observatory, which is jointly operated by the California Institute of Technology and the University of California.
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Blanton, E.L., Gregg, M.D., Helfand, D.J., Becker, R.H., and White, R.L. 2003, Astronomical Journal, 125, 1635
Using a combination of near-infrared and optical photometry, along with multiobject spectroscopy, we have confirmed the existence of a high-redshift cluster of galaxies at z=0.96. The cluster was found using a wide-angle-tailed radio source selected from the VLA FIRST survey as a cluster signpost. These types of radio sources are often found in clusters and are thought to attain their C-shaped morphologies from the relative motion between the radio source host galaxy and the intracluster medium. We present optical/near-infrared color-magnitude diagrams that show a concentration of cluster galaxies in color space. We also include spectroscopic results obtained from the Keck II Low Resolution Imaging Spectrometer. Ten galaxies are confirmed at the cluster redshift, with a line-of-sight velocity dispersion of sigma=530+190-90 km s-1, typical of an Abell richness class 0 cluster. Using data from the ROSAT public archive, we limit the X-ray luminosity for the cluster to LX,bol<~3x1044 ergs s-1, consistent with the value expected from the LX-? relation.
Based in part on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
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Bond, H.E., White, R.L., Becker, R.H., and O'Brien, M.S. 2002, Publ. Astron. Soc. Pacific, 114, 1359
We have identified the 1.4 GHz radio source FIRST J102347.6+003841 (hereafter FIRST J1023+0038) with a previously unknown 17th magnitude Galactic cataclysmic variable (CV). The optical spectrum resembles that of a magnetic (AM Herculis or DQ Herculis type) CV. Five nights of optical CCD photometry showed variations on timescales of minutes to hours, along with rapid flickering. A reexamination of the FIRST radio-survey data reveals that the radio detection was based on a single 6.6 mJy flare; on two other occasions, the source was below the ~1 mJy survey limit. Several other magnetic CVs are known to be variable radio sources, suggesting that FIRST J1023+0038 is a new member of this class (and the first CV to be discovered on the basis of radio emission). However, FIRST J1023+0038 is several optical magnitudes fainter than the other radio-detected magnetic CVs. It remains unclear whether the source simply had a very rare and extraordinarily intense radio flare at the time of the FIRST observation, or is really an unusually radio-luminous CV; thus, further observations are urged.
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Ivezic, Z., et al. 2002, Astronomical Journal, 124, 2364
We discuss the optical and radio properties of ~30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 1.5" with a Sloan Digital Sky Survey (SDSS) (optical, sensitive to r*~22.2) source in 1230 deg2 of sky. The matched sample represents ~30% of the 108,000 FIRST sources and 0.1% of the 2.5x107 SDSS sources in the studied region. SDSS spectra are available for 4300 galaxies and 1154 quasars from the matched sample and for a control sample of 140,000 galaxies and 20,000 quasars in 1030 deg2 of sky. Here we analyze only core sources, which dominate the sample; the fraction of SDSS-FIRST sources with complex radio morphology is determined to be less than 10%. This large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings. The majority (83%) of the FIRST sources identified with an SDSS source brighter than r*=21 are optically resolved; the fraction of resolved objects among the matched sources is a function of the radio flux, increasing from ~50% at the bright end to ~90% at the FIRST faint limit. Nearly all optically unresolved radio sources have nonstellar colors indicative of quasars. We estimate an upper limit of ~5% for the fraction of quasars with broadband optical colors indistinguishable from those of stars. The distribution of quasars in the radio flux-optical flux plane suggests the existence of the "quasar radio dichotomy" 8% ± 1% of all quasars with i*<18.5 are radio-loud, and this fraction seems independent of redshift and optical luminosity. The radio-loud quasars have a redder median color by 0.08 ± 0.02 mag, and show a 3 times larger fraction of objects with extremely red colors. FIRST galaxies represent 5% of all SDSS galaxies with r*<17.5, and 1% for r*<20, and are dominated by red (u*-r*>2.22) galaxies, especially those with r*>17.5. Magnitude- and redshift-limited samples show that radio galaxies have a different optical luminosity distribution than nonradio galaxies selected by the same criteria; when galaxies are further separated by their colors, this result remains valid for both blue and red galaxies. For a given optical luminosity and redshift, the observed optical colors of radio galaxies are indistinguishable from those of all SDSS galaxies selected by identical criteria. The distributions of radio-to-optical flux ratio are similar for blue and red galaxies in redshift-limited samples; this similarity implies that the difference in their luminosity functions and resulting selection effects are the dominant cause for the preponderance of red radio galaxies in flux-limited samples. The fraction of radio galaxies whose emission-line ratios indicate an AGN (30%), rather than starburst, origin is 6 times larger than the corresponding fraction for all SDSS galaxies (r*<17.5). We confirm that the AGN-to-starburst galaxy number ratio increases with radio flux and find that radio emission from AGNs is more concentrated than radio emission from starburst galaxies.
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Lacy, M., Gregg, M., Becker, R.H., White, R.L., Glikman, E., Helfand, D., and Winn, J.N. 2002,, Astronomical Journal, 123, 2925
We report the discovery of a z=2.65 low-ionization iron broad absorption line quasar, FIRST J100424.9+122922, which is gravitationally lensed by a galaxy at z~0.95. The object was discovered as part of a program to find very red quasars by matching the FIRST radio survey with the Two Micron All Sky Survey in the near-infrared. J100424.9+122922 is the second lensed system to be found in this program, suggesting that many gravitational lenses are probably missed from conventional optical quasar surveys. We have made a simple lens model and a rough estimate of the reddening in the immediate environment of the quasar which suggests that the quasar is intrinsically very luminous and is accreting at close to the Eddington limit of its ~109 Msolar black hole. The lensing galaxy has a small amount of dust, which is responsible for some excess reddening observed in the fainter image of the quasar, but is otherwise a fairly typical massive elliptical galaxy. We model the selection effects working against the detection of red quasars in both lensed and unlensed samples. We show that these selection effects are very effective at removing even lightly reddened high-redshift quasars from magnitude-limited samples, whether they are lensed or not. This suggests that the red quasar population in general could be very large, and in particular the class of iron broad absorption line quasars of which J100424.9+122922 is a member may be much larger than their rarity in magnitude-limited samples would suggest.
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de Kool, M., Becker, R.H., Arav, N., Gregg, M.D., and White, R.~L. 2002,, Astrophysical Journal, 570, 514
A Keck echelle spectrum of the quasar FBQS 0840+3633 reveals outflowing gas that gives rise to blueshifted absorption lines of many low-ionization species. The gas covers a range of velocities from -700 to -3500 km s-1, with two main components centered at -900 and -2800 km s-1. The physical conditions in the two main velocity components are found to be significantly different and can be attributed to a difference of a factor of ~100 in the distance from the central continuum source. The low-velocity gas shows absorption lines from excited states with relative strengths that indicate a low density. The level populations of low-lying Ni II, Si II, and Fe II states cannot be explained with a model based on collisional excitation and a single electron density. The lines of Si II provide an upper limit on the electron density of ne<500 cm-3, and another excitation mechanism must be responsible for the observed excitation of Fe II and Ni II. Assuming that this mechanism is UV fluorescence leads to an estimate of the distance between the low-velocity gas and the active nucleus of ~230 pc. Absorption lines from excited states formed in the high-velocity gas indicate a much higher density. This gas gives rise to Fe III and strong Al III absorption, which indicates that it contains the hydrogen ionization front on our line of sight to the active nucleus. The observed Fe III and Al III column densities and the absence of detectable absorption from the He I 23S state allow us to derive an estimate of the typical distance between the high-velocity gas and the active nucleus of ~1 pc. Based on observations obtained with the W. M. Keck Observatory, which is jointly operated by the California Institute of Technology and the University of California, and the Multiple Mirror Telescope Observatory, which is jointly operated by the University of Arizona and the Smithsonian Institution.
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Richards, G.T., Gregg, M.D., Becker, R.H., and White, R.L. 2002, Astrophysical Journal Letters, 567, L13
We present a Keck Observatory/Echelle Spectrograph and Imager spectrum of FIRST 074711.2+273904, a K=15.4 quasar with a redshift of 4.11 that is detected by both the Faint Images of the Radio Sky at Twenty cm (FIRST) survey and the Two Micron All Sky Survey (2MASS). The spectrum contains at least 14 independent C IV absorption systems longward of the Ly-alpha forest. These systems are found over a path length of delta z=0.984, constituting one of the highest densities per unit redshift of C IV absorption ever observed. One of the C IV systems is troughlike and resembles a weak broad absorption line (BAL)-type outflow. Two of the C IV are "associated" absorption systems with |v|<3000 km s-1. Of the 11 remaining systems with v>3000 km s-1, eight are either resolved or require multiple discrete systems to fit the line profiles. In addition to C IV absorption, there are two low-ionization Mg II absorption systems, along with two damped Ly-alpha systems, at least one of which may be a C IV system. The overdensity of C IV absorption spans a redshift range of delta z~1. Superclusters along the line of sight are unlikely to cause an overdensity stretching over such a long redshift path; thus, the absorption may be an example of narrow, high-velocity intrinsic absorption that originates from the quasar. We suggest that this quasar is a member of a transitional class of BAL quasars, where we are just barely seeing the spatial, density, or temporal edge of the BAL-producing region (or period); the multiple high-velocity absorption systems may be the remnants (or precursors) of a stronger BAL outflow. If correct, then some simpler absorption-line complexes in other quasars may also be due to outflowing rather than to intervening material.
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de Kool, M., Becker, R.H., Gregg, M.D., White, R.L., and Arav, N. 2002, Astrophysical Journal, 567, 58
This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J121442.3+280329, covering the rest wavelength range from 2300 to 3500 A. The line of sight toward this quasar (QSO) contains an outflow giving rise to many blueshifted absorption lines. The outflow consists of material with a continuous range of velocities from -1200 to -2800 km s-1. Significant substructure is present in the absorption line profiles. The spectrum is dominated by absorption lines of Mg II and the singly ionized iron group elements Fe II, Cr II, and Mn II, including absorption lines from excited levels with energies above 30,000 cm-1 (~4 eV).We derive constraints on the physical conditions in the outflow by fitting a model to the observed spectrum that simultaneously optimizes the values for the column densities of all species, the excitation temperature, the shape of the unabsorbed continuum, and the covering factor. By comparing these constraints with ionization models, we conclude that the ionization parameter, density, and column density of the outflow is characterized by -2.0<logU<-0.7, 7.5<lognH<9.5, and 21.4<logNH<22.2. These values place the absorbing outflow at a distance between 1 and 30 pc from the QSO core. Based on observations obtained with the W. M. Keck Observatory, which is jointly operated by the California Institute of Technology and the University of California, and the Multiple Mirror Telescope Observatory, which is jointly operated by the University of Arizona and the Smithsonian Institution.
This paper is available through ADS.
McMahon, R.G., Helfand, D.J., White, R.L. and Becker, R.H. 2002, Astrophysical Journal Supplement Series, 143, 1
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, 121, 2915
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.
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 ADS and 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).
Leighly, K.M., Halpern, J.P., Helfand, D.J., Becker, R.H., and Impey, C.D. 2001, Astronomical Journal, 121, 2889
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 ADS and the astro-ph e-print archives.
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<z<0.85. Furthermore, we cannot rule out that the other two bent doubles may be associated with clusters at higher redshift. Richness measurements indicate that these clusters are typical of the majority of those found in the Abell catalog, with a range of Abell richness classes from 0 to 2. The line-of-sight velocity dispersions are very different from cluster to cluster, ranging from approximately 300 to 1100 km s-1. At the upper end of these intervals, we may be sampling some of the highest redshift massive clusters known. Alternatively, the large velocity dispersions measured in some of the clusters may indicate that they are merging systems with significant substructure, consistent with recent ideas concerning WAT formation (Burns et al.).
Based in part on observations obtained at the W. M. Keck Observatory.
This paper is available through ADS.
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=0.134.
This paper is available through ADS.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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, compressed Postscript, and through the ADS.
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.
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.
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 available in both HTML and compressed Postscript, as well as through the ADS. 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
Over the next decade the Very Large Array (VLA) will carry out a systematic survey of the northern sky at 20 cm wavelength in two configurations. We have selected as a moniker the acronym FIRST, which in uncompressed form reads Faint Images of the Radio Sky at Twenty-cm. The high-resolution survey will be done in B configuration and hence will achieve an angular resolution of 5 arcsec. It will cover a 104 square degree region centered on the north Galactic pole. Each field will be observed for ~3 minutes with a resulting rms noise level of ~0.2 mJy. The survey will result in a catalog of 106 discrete sources as well as 65,000 images each composed of 4x106 pixels. To expedite the massive data analysis task this project entails, we have decided to utilize computers.
It is our intention to release to the community compressed, machine-readable copies of all the images as well as an annotated catalog of sources. The challenge will be to accomplish this with a minimum of resources. We hope to automate maximally the data analysis pipeline to achieve this end. This paper describes the history of the project, its current status, and our data analysis methods, followed by a brief resumé of FIRST's expected scientific impact.
This is the first-published paper describing the FIRST project and is available in HTML and compressed Postscript.
