Gordon T. Richards
A5039806724- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Stellar, planetary, and galactic studies
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Astrophysics and Star Formation Studies
- Radio Astronomy Observations and Technology
- Cosmology and Gravitation Theories
- Scientific Research and Discoveries
- Remote Sensing in Agriculture
- Adaptive optics and wavefront sensing
- Geophysics and Gravity Measurements
- CCD and CMOS Imaging Sensors
- Pulsars and Gravitational Waves Research
- Calibration and Measurement Techniques
- Gaussian Processes and Bayesian Inference
- Dark Matter and Cosmic Phenomena
- Relativity and Gravitational Theory
- History and Developments in Astronomy
- Particle Accelerators and Free-Electron Lasers
- Statistical and numerical algorithms
- Algorithms and Data Compression
- Nuclear Physics and Applications
Drexel University
2015-2024
Georgia Institute of Technology
2015-2017
State Street (United States)
2015-2017
Max Planck Institute for Astronomy
2013-2016
Association of Universities For Research In Astronomy
2014
U.S. National Science Foundation
2014
Kitt Peak National Observatory
2014
Max Planck Society
2013
Johns Hopkins University
2006-2008
Princeton University
2003-2008
We examine the properties of host galaxies 22,623 narrow-line AGN with 0.02
The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere collect spectra ≈106 galaxies, 100,000 quasars, 30,000 stars, serendipity targets. In 2001 June, SDSS released to general astronomical community its early data release, roughly 462 deg2 including almost 14 million detected objects 54,008 follow-up spectra. were collected in drift-scan mode five bandpasses (u, g, r, i, z); our 95% completeness...
We have created a variety of composite quasar spectra using homogeneous data set over 2200 from the Sloan Digital Sky Survey (SDSS). The sample spans redshift range 0.044 ≤ z 4.789 and an absolute r' magnitude -18.0 to -26.5. input cover observed wavelength 3800–9200 Å at resolution 1800. median covers rest-wavelength 800 8555 reaches peak signal-to-noise ratio 300 per 1 element in rest frame. identified 80 emission-line features spectrum. Emission-line shifts relative nominal laboratory...
We study the evolution of ionization state IGM at end reionization epoch using spectra a sample nineteen quasars 5.745.7: optical depth changes from tau ~ (1+z)^{4.3} to (1+z)^{>11}, and average length dark gaps with tau>3.5 increases <10 >80 comoving Mpc. The dispersion properties along different lines sight also rapidly, implying fluctuations by factor >4 in UV background z>6, when mean free path photons is comparable correlation galaxies. shows most dramatic increase...
We present an analysis of the mid-infrared (MIR) and optical properties type 1 (broad-line) quasars detected by Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ~ 3, with predictions = 7. demonstrate how combining colors can yield even more efficient selection active galactic nuclei (AGNs) than or alone. Composite spectral energy distributions (SEDs) are constructed for 259 both Sloan Digital Sky Survey photometry, supplemented near-IR, GALEX, VLA, ROSAT data,...
The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained ≈240,000 moderate-resolution (R ∼ 1800) spectra from 3900 Å to 9000 of fainter Milky Way stars (14.0 < g 20.3) a wide variety spectral types, both main-sequence evolved objects, with the goal studying kinematics populations our Galaxy its halo. are clustered in 212 regions spaced over three quarters sky. Radial velocity accuracies at 18, degrading 20. For signal-to-noise ratio >10 per resolution element,...
We combine a large set of quasar luminosity function (QLF) measurements from the rest-frame optical, soft and hard X-ray, near- mid-IR bands to determine bolometric QLF in redshift interval z = 0-6. Accounting for observed distributions column densities variation SED shapes, as well their dependence on luminosity, makes it possible integrate observations reliable manner provides baseline larger than that any individual survey. infer break faint-end slope out ~ 4.5 confirm at high...
We describe the algorithm for selecting quasar candidates optical spectroscopy in Sloan Digital Sky Survey. Quasar are selected via their non-stellar colors "ugriz" broad-band photometry, and by matching unresolved sources to FIRST radio catalogs. The automated is sensitive quasars at all redshifts lower than z=5.8. Extended also targeted as low-redshift order investigate evolution of Active Galactic Nuclei (AGN) faint end luminosity function. Nearly 95% previously known recovered (based on...
We present the fifth edition of Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon SDSS Seventh Data Release. The catalog, contains 105,783 spectroscopically confirmed quasars, represents conclusion SDSS-I and SDSS-II quasar survey. catalog consists objects that have luminosities larger than M_i = -22.0 (in a cosmology with H_0 70 km/s/Mpc Omega_M 0.3, Omega_Lambda 0.7) at least one emission line FWHM 1000 km/s or interesting/complex absorption features, are fainter i > 15.0...
We present a compilation of properties the 105,783 quasars in SDSS Data Release 7 (DR7) quasar catalog. In this value-added product, we compile continuum and emission line measurements around Halpha, Hbeta, MgII CIV regions, as well other quantities such radio properties, broad absorption (BALQSO) flags, disk emitters. also virial black hole mass estimates based on various calibrations. For fiducial use Vestergaard & Peterson (VP06) calibrations for Hbeta CIV, our own calibration which...
We present the results from a survey of i-dropout objects selected ∼1550 deg2 multicolor imaging data Sloan Digital Sky Survey to search for luminous quasars at z ≳ 5.8. Objects with i*-z* > 2.2 and z* < 20.2 are selected, follow-up J-band photometry is used separate L- T-type cool dwarfs high-redshift quasars. describe discovery three new quasars, SDSSp J083643.85+005453.3 (z = 5.82), J130608.26+035626.3 5.99), J103027.10+052455.0 6.28). The quasar radio source flux 1.1 mJy 20 cm. spectra...
We present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). find that Lyα absorption in spectra these evolves strongly with redshift. To ∼ 5.7, as expected from an extrapolation lower redshifts. However, highest-redshift object, SDSSp J103027.10+052455.0 (z 6.28), average transmitted flux is 0.0038 ± 0.0026 times continuum level over 8450 Å < λ 8710 (5.95 zabs 6.16), consistent zero flux. Thus drops a factor...
We determine the number counts and z = 0-5 luminosity function for a well-defined, homogeneous sample of quasars from Sloan Digital Sky Survey (SDSS). conservatively define most uniform statistical possible, consisting 15,343 within an effective area 1622 deg2 that was derived parent 46,420 spectroscopically confirmed broad-line in 5282 imaging data SDSS Data Release 3. The extends i 15 to 19.1 at ≲ 3 20.2 ≳ agree well with results Two Degree Field QSO Redshift (2QZ) redshifts luminosities...
We present the discovery of three new quasars at z > 6 in ∼ 1300 deg2 Sloan Digital Sky Survey imaging data, J114816.64+525150.3 (z = 6.43), J104845.05+463718.3 6.23), and J163033.90+401209.6 6.05). The first two objects have weak Lyα emission lines; their redshifts are determined from positions Lyman break. They only accurate to ∼0.05 could be affected by presence broad absorption line systems. last object has a strength more typical lower redshift quasars. Based on sample six 5.7 that...
We investigate the extent to which Palomar-Green (PG) Bright Quasar Survey (BQS) is complete and representative of general quasar population by comparing it with imaging spectroscopy from Sloan Digital Sky (SDSS). A comparison SDSS PG photometry both stars quasars reveals need apply a color magnitude recalibration data. Using photometric catalog, we define PG's parent sample objects that are not main-sequence simulate selection this using criteria errors. This simulation shows effective U -...
The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with unique combination of high angular resolution ($\approx$2.5"), sensitivity (a 1$\sigma$ goal 70 $\mu$Jy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). first observations began September 2017, observing for will finish 2024. VLASS use approximately 5500 hours on Karl G. Jansky (VLA) to cover whole visible VLA (Declination $>-40^{\circ}$), total...
We compile black hole (BH) masses for ~60,000 quasars in the redshift range 0.1≲ z≲ 4.5 included Fifth Data Release of Sloan Digital Sky Survey, using virial BH mass estimators based on Hβ, Mg II, and C IV emission lines. Within our sample, widths three lines follow lognormal distributions, with means dispersions that do not depend strongly luminosity or redshift. The II- Hβ-estimated are consistent one another, but there is a positive bias between IV- II-estimated correlated IV-Mg II...
We discuss the optical and radio properties of ∼30,000 FIRST (radio, 20 cm, sensitive to 1 mJy) sources positionally associated within 15 with a Sloan Digital Sky Survey (SDSS) (optical, r* ∼ 22.2) source in 1230 deg2 sky. The matched sample represents ∼30% 108,000 0.1% 2.5 × 107 SDSS studied region. spectra are available for 4300 galaxies 1154 quasars from control 140,000 20,000 1030 Here we analyze only core sources, which dominate sample; fraction SDSS-FIRST complex morphology is...
We present the discovery of seven quasars at z > 5.7, selected from ∼2000 deg2 multicolor imaging data Sloan Digital Sky Survey. The new have redshifts 5.79 to 6.13. Five are as part a complete flux-limited sample in SDSS northern Galactic cap; two larger photometric errors and not sample. One quasars, J1335+3533 (z = 5.93), exhibits no emission lines; 3 σ limit on rest-frame equivalent width Lyα+N V line is 5 Å. It highest redshift lineless quasar known could be gravitational lensed galaxy,...
Abstract We summarize the Sloan Digital Sky Survey data acquisition and processing steps, describe runQA , a pipeline designed for automated quality assessment. In particular, we show how position of stellar locus in color‐color diagrams can be used to estimate accuracy photometric zeropoint calibration better than 0.01 mag 0.03 deg 2 patches. Using this method, that typical errors SDSS imaging are not larger ∼0.01 g r i bands, 0.02 z band, u band (root‐mean‐scatter offsets). (© 2004...
We present the fourth edition of Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog contains 77,429 objects; this is an increase over 30,000 entries since previous edition. consists objects in SDSS Fifth Data Release that have luminosities larger than Mi = -22.0 (in a cosmology with H0 70 km s-1 Mpc-1, ΩM 0.3, and ΩΛ 0.7), at least one emission line FWHM 1000 or interesting/complex absorption features, are fainter i ≈ 15.0, highly reliable redshifts. area covered by ≈5740 deg2....
Using a sample of over 25,000 spectroscopically confirmed quasars from the Sloan Digital Sky Survey, we show how quasar variability in rest-frame optical/UV regime depends on time lag, luminosity, rest wavelength, redshift, presence radio and X-ray emission, broad absorption line systems. Imaging photometry is compared with three-band spectrophotometry obtained at later epochs spanning lags up to about 2 yr. The large size wide range parameter values allow dependence be isolated as function...
Using a sample of 30,000 quasars from SDSS-DR7, we explore the range properties exhibited by high-ionization, broad emission lines, such as CIV 1549. Specifically investigate anti-correlation between L_UV and line EQW (the Baldwin Effect) "blueshifting" high-ionization lines. The blueshift is nearly ubiquitous, with mean shift 810 km/s for radio-quiet (RQ) 360 radio-loud (RL) quasars, Effect present in both RQ RL samples. Composite spectra are constructed function attempt to reveal empirical...
We present a total of 4784 unique broad absorption line quasars from the Sloan Digital Sky Survey Third Data Release. An automated algorithm was used to match continuum each quasar and identify regions flux at least 10% below over velocity range 1000 km/s in CIV MgII regions. The model selected as best-fit set template spectra binned luminosity, emission width, redshift, with power-law spectral index amount dust reddening additional free parameters. characterize our sample through...