Astron.J. 123 (2002) 567-577 We present the first edition of the Sloan Digital Sky Survey (SDSS) Quasar
Catalog. The catalog consists of the 3814 objects (3000 discovered by the SDSS)
in the initial ...SDSS public data release that have at least one emission line
with a full width at half maximum larger than 1000 km/s, luminosities brighter
than M_i^* = -23, and highly reliable redshifts. The area covered by the
catalog is 494 square degrees; the majority of the objects were found in SDSS
commissioning data using a multicolor selection technique. The quasar redshifts
range from 0.15 to 5.03. For each object the catalog presents positions
accurate to better than 0.2" rms per coordinate, five band (ugriz) CCD-based
photometry with typical accuracy of 0.05 mag, radio and X-ray emission
properties, and information on the morphology and selection method. Calibrated
spectra of all objects in the catalog, covering the wavelength region 3800 to
9200 Angstroms at a spectral resolution of 1800-2100, are also available. Since
the quasars were selected during the commissioning period, a time when the
quasar selection algorithm was undergoing frequent revisions, the sample is not
homogeneous and is not intended for statistical analysis.
We investigate the extent to which the Palomar-Green (PG) Bright Quasar Survey (BQS) is complete and representative of the general quasar population by comparing with imaging and spectroscopy from ...the Sloan Digital Sky Survey. A comparison of SDSS and PG photometry of both stars and quasars reveals the need to apply a color and magnitude recalibration to the PG data. Using the SDSS photometric catalog, we define the PG's parent sample of objects that are not main-sequence stars and simulate the selection of objects from this parent sample using the PG photometric criteria and errors. This simulation shows that the effective U-B cut in the PG survey is U-B < -0.71 (rather than the intended U-B < -0.44), implying a color-related incompleteness. As the color distribution of bright quasars peaks near U-B=-0.7 and the 2-sigma error in U-B is comparable to the full width of the color distribution of quasars, the color incompleteness of the BQS is approximately 50% and essentially random with respect to U-B color for z<0.5. There is, however, a bias against bright quasars at 0.5 < z < 1, which is induced by the color-redshift relation of quasars (although quasars at z>0.5 are inherently rare in bright surveys in any case). We find no evidence for any other systematic incompleteness when comparing the distributions in color, redshift, and FIRST radio properties of the BQS and a BQS-like subsample of the SDSS quasar sample. However, the application of a bright magnitude limit biases the BQS toward the inclusion of objects which are blue in g-i, in particular compared to the full range of g-i colors found among the i-band limited SDSS quasars, and even at i-band magnitudes comparable to those of the BQS objects.
Astron.J.126:2209,2003 Many open questions in X-ray astronomy are limited by the relatively small
number of objects in uniform optically-identified samples, especially when rare
subclasses are ...considered, or subsets isolated to search for evolution or
correlations between wavebands. We describe initial results of a program aimed
to ultimately yield 10^4 X-ray source identifications--a sample about an order
of magnitude larger than earlier efforts. The technique employs X-ray data from
the ROSAT All-Sky Survey (RASS), and optical imaging and spectroscopic followup
from the Sloan Digital Sky Survey (SDSS). Optical objects in the SDSS catalogs
are automatically cross-correlated with RASS X-ray source positions; then
priorities for follow-on SDSS optical spectra of candidate counterparts are
automatically assigned using an algorithm based on the known fx/fopt ratios for
various classes of X-ray emitters. SDSS parameters for optical morphology,
magnitude, colors, plus FIRST radio data, serve as proxies for object class.
Initial application of this approach to 1400 deg^2 of sky provides a catalog
of 1200 spectroscopically confirmed quasars/AGN that are probable RASS
identifications. Most of the IDs are new, and only a few percent of the AGN are
likely to be random superpositions. The magnitude and redshift ranges of the
counterparts extend over 15<m<21 and 0.03<z<3.6. Although most IDs are quasars
and Sy 1s, a variety of other AGN subclasses are also sampled. Substantial
numbers of rare AGN are found, including more than 130 narrow-line Seyfert 1s
and 45 BL Lac candidates. These results already provide a sizeable set of new
IDs, show utility of the sample in multi-waveband studies, and demonstrate the
capability of the RASS/SDSS approach to efficiently proceed towards the largest
homogeneously selected/observed sample of X-ray emitting AGN. Abridged Abstract
Astron.J.123:2945,2002 We describe the algorithm for selecting quasar candidates for optical
spectroscopy in the Sloan Digital Sky Survey. Quasar candidates are selected
via their non-stellar colors ...in "ugriz" broad-band photometry, and by matching
unresolved sources to the FIRST radio catalogs. The automated algorithm is
sensitive to quasars at all redshifts lower than z=5.8. Extended sources are
also targeted as low-redshift quasar candidates in order to investigate the
evolution of Active Galactic Nuclei (AGN) at the faint end of the luminosity
function. Nearly 95% of previously known quasars are recovered (based on 1540
quasars in 446 square degrees). The overall completeness, estimated from
simulated quasars, is expected to be over 90%, whereas the overall efficiency
(quasars:quasar candidates) is better than 65%. The selection algorithm targets
ultraviolet excess quasars to i^*=19.1 and higher-redshift (z>3) quasars to
i^*=20.2, yielding approximately 18 candidates per square degree. In addition
to selecting ``normal'' quasars, the design of the algorithm makes it sensitive
to atypical AGN such as Broad Absorption Line quasars and heavily reddened
quasars.
We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform ...statistical sample possible, consisting of 15,343 quasars within an effective area of 1622 deg^2 that was derived from a parent sample of 46,420 spectroscopically confirmed broad-line quasars in the 5282 deg^2 of imaging data from SDSS Data Release Three. The sample extends from i=15 to i=19.1 at z<3 and to i=20.2 for z>3. The number counts and luminosity function agree well with the results of the 2dF QSO Survey, but the SDSS data probe to much higher redshifts than does the 2dF sample. The number density of luminous quasars peaks between redshifts 2 and 3, although uncertainties in the selection function in this range do not allow us to determine the peak redshift more precisely. Our best fit model has a flatter bright end slope at high redshift than at low redshift. For z<2.4 the data are best fit by a redshift-independent slope of beta = -3.1 (Phi(L) propto L^beta). Above z=2.4 the slope flattens with redshift to beta=-2.37 at z=5. This slope change, which is significant at a >5-sigma level, must be accounted for in models of the evolution of accretion onto supermassive black holes.
Astrophys.J.569:245-274,2002 We identify new structures in the halo of the Milky Way Galaxy from
positions, colors and magnitudes of five million stars detected in the Sloan
Digital Sky Survey. Most ...of these stars are within 1.26 degrees of the
celestial equator. We present color-magnitude diagrams (CMDs) for stars in two
previously discovered, tidally disrupted structures. The CMDs and turnoff
colors are consistent with those of the Sagittarius dwarf galaxy, as had been
predicted. In one direction, we are even able to detect a clump of red stars,
similar to that of the Sagittarius dwarf, from stars spread across 110 square
degrees of sky. Focusing on stars with the colors of F turnoff objects, we
identify at least five additional overdensities of stars. Four of these may be
pieces of the same halo structure, which would cover a region of the sky at
least 40 degrees in diameter, at a distance of 11 kpc from the Sun (18 kpc from
the center of the Galaxy). The turnoff is significantly bluer than that of
thick disk stars, and closer to the Galactic plane than a power-law spheroid.
We suggest two models to explain this new structure. One possibility is that
this new structure could be a new dwarf satellite of the Milky Way, hidden in
the Galactic plane, and in the process of being tidally disrupted. The other
possibility is that it could be part of a disk-like distribution of stars which
is metal-poor, with a scale height of approximately 2 kpc and a scale length of
approximately 10 kpc. The fifth overdensity, which is 20 kpc away, is some
distance from the Sagittarius dwarf streamer orbit and is not associated with
any known structure in the Galactic plane. It is likely that there are many
smaller streams of stars in the Galactic halo.
We present the first edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 3814 objects (3000 discovered by the SDSS) in the initial SDSS public data release that ...have at least one emission line with a full width at half maximum larger than 1000 km/s, luminosities brighter than M_i^* = -23, and highly reliable redshifts. The area covered by the catalog is 494 square degrees; the majority of the objects were found in SDSS commissioning data using a multicolor selection technique. The quasar redshifts range from 0.15 to 5.03. For each object the catalog presents positions accurate to better than 0.2" rms per coordinate, five band (ugriz) CCD-based photometry with typical accuracy of 0.05 mag, radio and X-ray emission properties, and information on the morphology and selection method. Calibrated spectra of all objects in the catalog, covering the wavelength region 3800 to 9200 Angstroms at a spectral resolution of 1800-2100, are also available. Since the quasars were selected during the commissioning period, a time when the quasar selection algorithm was undergoing frequent revisions, the sample is not homogeneous and is not intended for statistical analysis.
We present the second edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of 16713 objects in the SDSS First Data Release (DR1) that have luminosities larger than ...M_i=-22 (H_0=70 km/s, Omega_M=0.3, Omega_Lambda=0.7), have at least one emission line with FWHM larger than 1000 km/s, and have highly reliable redshifts. The area covered is ~1360 deg^2 and the redshifts range from 0.08 to 5.41, with a median value of 1.43. Each object has positions accurate to better than 0.2" rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method, in addition to radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large area surveys. Calibrated digital spectra covering 3800-9200 Angstroms at a spectral resolution 1800-2100, are available. This publication supersedes the first SDSS Quasar Catalog, which was based on material from the SDSS Early Data Release. A summary of corrections to current quasar databases is provided. The majority of the objects were found in SDSS commissioning data using a multicolor selection technique. Since the quasar selection algorithm was undergoing testing during the entire DR1 observational period, care must be taken when assembling samples for use in statistical studies. A total of 15786 objects (94%) in the catalog were discovered by the SDSS; 12,173 of which are reported here for the first time, including five quasars brighter than i=16.0 and 17 quasars with redshifts larger than 4.5.
Many open questions in X-ray astronomy are limited by the relatively small number of objects in uniform optically-identified samples, especially when rare subclasses are considered, or subsets ...isolated to search for evolution or correlations between wavebands. We describe initial results of a program aimed to ultimately yield 10^4 X-ray source identifications--a sample about an order of magnitude larger than earlier efforts. The technique employs X-ray data from the ROSAT All-Sky Survey (RASS), and optical imaging and spectroscopic followup from the Sloan Digital Sky Survey (SDSS). Optical objects in the SDSS catalogs are automatically cross-correlated with RASS X-ray source positions; then priorities for follow-on SDSS optical spectra of candidate counterparts are automatically assigned using an algorithm based on the known fx/fopt ratios for various classes of X-ray emitters. SDSS parameters for optical morphology, magnitude, colors, plus FIRST radio data, serve as proxies for object class. Initial application of this approach to 1400 deg^2 of sky provides a catalog of 1200 spectroscopically confirmed quasars/AGN that are probable RASS identifications. Most of the IDs are new, and only a few percent of the AGN are likely to be random superpositions. The magnitude and redshift ranges of the counterparts extend over 15<m<21 and 0.03<z<3.6. Although most IDs are quasars and Sy 1s, a variety of other AGN subclasses are also sampled. Substantial numbers of rare AGN are found, including more than 130 narrow-line Seyfert 1s and 45 BL Lac candidates. These results already provide a sizeable set of new IDs, show utility of the sample in multi-waveband studies, and demonstrate the capability of the RASS/SDSS approach to efficiently proceed towards the largest homogeneously selected/observed sample of X-ray emitting AGN. Abridged Abstract
We describe the algorithm for selecting quasar candidates for optical spectroscopy in the Sloan Digital Sky Survey. Quasar candidates are selected via their non-stellar colors in "ugriz" broad-band ...photometry, and by matching unresolved sources to the FIRST radio catalogs. The automated algorithm is sensitive to quasars at all redshifts lower than z=5.8. Extended sources are also targeted as low-redshift quasar candidates in order to investigate the evolution of Active Galactic Nuclei (AGN) at the faint end of the luminosity function. Nearly 95% of previously known quasars are recovered (based on 1540 quasars in 446 square degrees). The overall completeness, estimated from simulated quasars, is expected to be over 90%, whereas the overall efficiency (quasars:quasar candidates) is better than 65%. The selection algorithm targets ultraviolet excess quasars to i^*=19.1 and higher-redshift (z>3) quasars to i^*=20.2, yielding approximately 18 candidates per square degree. In addition to selecting ``normal'' quasars, the design of the algorithm makes it sensitive to atypical AGN such as Broad Absorption Line quasars and heavily reddened quasars.
