Red and Reddened Quasars in the Sloan Digital Sky Survey

By Gordon Richards, P. Hall, D. V. vanden Berk, M. Strauss, D. Schneider, M. Weinstein, T. Reichard, D. York, G. Knapp, Xiaohui Fan and 5 more. 2003

323 citations recorded by the source corpus.

We investigate the overall continuum and emission-line properties of quasars as a function of their optical/UV spectral energy distributions. Our sample consists of 4576 quasars from the Sloan Digital Sky Survey (SDSS) that were chosen using homogeneous selection criteria. Expanding on our previous work, which demonstrated that the optical/UV color distribution of quasars is roughly Gaussian but with a red tail, here we distinguish between (1) quasars that have intrinsically blue (optically flat) power-law continua, (2) quasars that have intrinsically red (optically steep) power-law continua, and (3) quasars whose colors are inconsistent with a single power-law continuum. We find that 273 (6.0%) of the quasars in our sample fall into the latter category and appear to be redder because of SMC-like dust extinction and reddening rather than because of synchrotron emission. Even though the SDSS quasar survey is optically selected and flux-limited, we demonstrate that it is sensitive to dust reddened quasars with E(B-V) ≲ 0.5, assuming a classical SMC extinction curve. The color distribution of our SDSS quasar sample suggests that the population of moderately dust reddened, but otherwise normal (i.e., type 1) quasars is smaller than the population of unobscured quasars: we estimate that a further 10% of the quasar population with Mi < -25.61 is missing from the SDSS sample because of extinction, bringing the total fraction of dust-reddened quasars to 15% of broad-line quasars. We also investigate the emission- and absorption-line properties of these quasars as a function of color and comment on how some of these results relate to Boroson-Green–type eigenvectors. Quasars with intrinsically red (optically steep) power-law continua tend to have narrower Balmer lines and weaker C IV, C III], He II, and 3000 Å bump emission as compared with bluer (optically flatter) quasars. The change in strength of the 3000 Å bump appears to be dominated by the Balmer continuum and not by Fe II emission. The dust-reddened quasars have even narrower Balmer lines and weaker 3000 Å bumps, in addition to having considerably larger equivalent widths of [O II] and [O III] emission. The fraction of broad absorption line quasars (BALQSOs) increases from ∼3.4% for the bluest quasars to perhaps as large as 20% for the dust-reddened quasars, but the intrinsic color distribution will be much bluer if all BALQSOs are affected by dust reddening.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/3363c3015260a23b8431d087c9a7caa34a9784c3

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Citations in the corpus

A Unified, Merger-driven Model of the Origin of Starbursts, Quasars, the Cosmic X-Ray Background, Supermassive Black Holes, and Galaxy Spheroids (2005, background): “2001; Richards et al. 2001; Gregg et al. 2002; White et al. 2003; Richards et al. 2003), extending to very bright quasars strongly reddened by largeNHI.”
The Nuclear Reddening Curve for Active Galactic Nuclei and the Shape of the Infrared to X-Ray Spectral Energy Distribution (2003, background): “Similarly, Richards et al. (2003) show that SMClike reddening affects the spectra of a few percent of radioquiet quasars.”
Binary Quasars in the Sloan Digital Sky Survey: Evidence for Excess Clustering on Small Scales (2005, background): “Also notice that a long tail in this distribution extends even beyond 2 100 because of outliers from the median color–redshift relation of quasars (Richards et al. 2001a), caused by broad absorption line features (Richards et al. 2003) or reddening (Hopkins et al. 2004).”
The luminosity dependence of the type 1 active galactic nucleus fraction (2005, background): “…include all such objects (accounting for the uncertainty in the starburst–Seyfert classification), whereas the optical colour selection used to select QSOs will exclude a population of red QSOs which may exist in significant numbers (Webster et al. 1995; Benn et al. 1998; Richards et al. 2003).”
Continuum and Emission-Line Properties of Broad Absorption Line Quasars (2003, methodology): “In Figure 8 we compare our HiBAL and LoBAL composite spectra in the spectral region covering the C iv and C iii] emission lines to the C iv shift composites (left) from Richards et al. (2002b) and to the color composite spectra (right) from Richards et al. (2003).”
Photometric redshifts in the SWIRE Survey (2008, methodology): “For QSOs we used an LMC-type extinction, following Richards et al (2003).”
x-cigale: fitting AGN/galaxy SEDs from X-ray to infrared (2020, background): “For example, Richards et al. (2003) found only ≈ 6% of their SDSS quasars are extincted.”
Spectral Energy Distributions and Multiwavelength Selection of Type 1 Quasars (2006, background): “Thus, the fraction of dust-reddened/extincted type 1 quasars (e.g., Richards et al. 2003; Glikman et al. 2004) that might be missed by an optical survey with UVX color-selection is no larger than 30%.”
Average extinction curves and relative abundances for quasi-stellar object absorption-line systems at 1 ≤zabs < 2 (2006, methodology): “Richards et al. (2003) showed that an observer frame colour excess, hereafter,∆(g − i), which is the difference between the actual colours of a QSO and the median colours of QSOs at that redshift, could be defined for the SDSS QSO spectra and could be used to form templates of objects with apparent…”
THE SLOAN DIGITAL SKY SURVEY QUASAR CATALOG. V. SEVENTH DATA RELEASE (2010, background): “The distribution of Δ(g − i) near the modal curve is roughly symmetric, but the lower left panel in Figure 5 reveals a significant population of “red” quasars that has no “blue” counterpart (also see Richards et al. 2003 and York et al. 2006).”
Soft X-Ray and Ultraviolet Emission Relations in Optically Selected AGN Samples (2005, methodology): “AGNs are targeted for spectroscopy based on a four-dimensional color-selection algorithm that is highly efficient and able to select AGNs redder than traditional UV-excess selection surveys (Richards et al. 2002, 2003; Hopkins et al. 2004).”
THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE (2012, methodology): “For example, Richards et al. (2003) and Hopkins et al. (2004) find that ∼ 20% of SDSS quasars have colors consistent with reddening from dust with an SMC-like extinction curve with E(B − V ) & 0.1.”
An Observational Determination of the Bolometric Quasar Luminosity Function (2006, methodology): “…above yields a best-fit uncorrelated dispersion component 0.1 dex, consistent with observational estimates of the scatter in band luminosities owing to these effects (e.g., Elvis et al.1994; George et al. 1998; Vanden Berk et al. 2001; Perola et al. 2002; Richards et al. 2003; Hopkins et al. 2004).”
On the Origin of [O II] Emission in Red-Sequence and Poststarburst Galaxies (2005, background): “Richards et al. (2003) found that dust-reddened QSOs have stronger [O ii] emission than normal QSOs.”
Four Quasars above Redshift 6 Discovered by the Canada-France High-z Quasar Survey (2007, background): “This is considerably redder than typical quasars which haveαν = 0.5 (Richards et al. 2003).”
A Catalog of Broad Absorption Line Quasars from the Sloan Digital Sky Survey Early Data Release (2003, background): “However, a significant fraction of quasars show evidence of dust reddening (e.g, Richards et al. 2003, Hopkins et al. 2004), which must be included in any automated continuum fitting procedure.”
COMPARING SINGLE-EPOCH VIRIAL BLACK HOLE MASS ESTIMATORS FOR LUMINOUS QUASARS (2012, background): “Rare objects with unusual continuum and/or emission line properties (for instance, dust reddened quasars, e.g., Richards et al. 2003) will lead to additional uncertainty in these virial mass estimates, alongwith measurement errors from poor spectral quality.”
The X-Ray-to-Optical Properties of Optically Selected Active Galaxies over Wide Luminosity and Redshift Ranges (2006, methodology): “Relative (i.e., redshift-corrected) colors can be us d to detect significant differences in the optical/UV continuuaof AGNs (Richards et al. 2003), so they can be used to compare the SDSS and COMBO-17 AGN populations.”
The Sloan Digital Sky Survey View of the Palomar-Green Bright Quasar Survey (2005, methodology): “…al. (2001) using DR1 data (Abazajian et al. 2003; changes in spectrophotometric calibration of SDSS data introduced in Data Release 2 [DR2] do not change the transformations appreciably) and the composite spectra from Richards et al. (2003) for quasars with different intrinsic colors and reddening.”
QUASAR CLUSTERING FROM SDSS DR5: DEPENDENCES ON PHYSICAL PROPERTIES (2008, methodology): “However, owing to the enormously large spatial volume probed and the fact that the quasar number density is much smaller than that of galaxies, the analysis of quasar clustering hasonly become practical in recent years, namely after large-scaleurveys such as the 2dF quasi-stellar object (QSO) redshi”