Red and reddened quasars in the sloan digital sky survey

Gordon T. Richards, Patrick B. Hall, Daniel E. Vanden Berk, Michael A. Strauss, Donald P. Schneider, Michael A. Weinstein, Timothy A. Reichard, Donald G. York, G. R. Knapp, Xiaohui Fan, Željko Ivezić, J. Brinkmann, Tamás Budavári, I. Csabai, R. C. Nichol

Research output: Contribution to journalArticle

250 Citations (Scopus)

Abstract

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 A bump emission as compared with bluer (optically flatter) quasars. The change in strength of the 3000 Åbump 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.

Original languageEnglish
Pages (from-to)1131-1147
Number of pages17
JournalAstronomical Journal
Volume126
Issue number3 1773
DOIs
Publication statusPublished - Sep 2003

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quasars
dust
power law
extinction
continuums
color
distribution
energy
spectral energy distribution

Keywords

  • Quasars: absorption lines
  • Quasars: emission lines
  • Quasars: general

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Richards, G. T., Hall, P. B., Vanden Berk, D. E., Strauss, M. A., Schneider, D. P., Weinstein, M. A., ... Nichol, R. C. (2003). Red and reddened quasars in the sloan digital sky survey. Astronomical Journal, 126(3 1773), 1131-1147. https://doi.org/10.1086/377014

Red and reddened quasars in the sloan digital sky survey. / Richards, Gordon T.; Hall, Patrick B.; Vanden Berk, Daniel E.; Strauss, Michael A.; Schneider, Donald P.; Weinstein, Michael A.; Reichard, Timothy A.; York, Donald G.; Knapp, G. R.; Fan, Xiaohui; Ivezić, Željko; Brinkmann, J.; Budavári, Tamás; Csabai, I.; Nichol, R. C.

In: Astronomical Journal, Vol. 126, No. 3 1773, 09.2003, p. 1131-1147.

Research output: Contribution to journalArticle

Richards, GT, Hall, PB, Vanden Berk, DE, Strauss, MA, Schneider, DP, Weinstein, MA, Reichard, TA, York, DG, Knapp, GR, Fan, X, Ivezić, Ž, Brinkmann, J, Budavári, T, Csabai, I & Nichol, RC 2003, 'Red and reddened quasars in the sloan digital sky survey', Astronomical Journal, vol. 126, no. 3 1773, pp. 1131-1147. https://doi.org/10.1086/377014
Richards GT, Hall PB, Vanden Berk DE, Strauss MA, Schneider DP, Weinstein MA et al. Red and reddened quasars in the sloan digital sky survey. Astronomical Journal. 2003 Sep;126(3 1773):1131-1147. https://doi.org/10.1086/377014
Richards, Gordon T. ; Hall, Patrick B. ; Vanden Berk, Daniel E. ; Strauss, Michael A. ; Schneider, Donald P. ; Weinstein, Michael A. ; Reichard, Timothy A. ; York, Donald G. ; Knapp, G. R. ; Fan, Xiaohui ; Ivezić, Željko ; Brinkmann, J. ; Budavári, Tamás ; Csabai, I. ; Nichol, R. C. / Red and reddened quasars in the sloan digital sky survey. In: Astronomical Journal. 2003 ; Vol. 126, No. 3 1773. pp. 1131-1147.
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T1 - Red and reddened quasars in the sloan digital sky survey

AU - Richards, Gordon T.

AU - Hall, Patrick B.

AU - Vanden Berk, Daniel E.

AU - Strauss, Michael A.

AU - Schneider, Donald P.

AU - Weinstein, Michael A.

AU - Reichard, Timothy A.

AU - York, Donald G.

AU - Knapp, G. R.

AU - Fan, Xiaohui

AU - Ivezić, Željko

AU - Brinkmann, J.

AU - Budavári, Tamás

AU - Csabai, I.

AU - Nichol, R. C.

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N2 - 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 A bump emission as compared with bluer (optically flatter) quasars. The change in strength of the 3000 Åbump 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.

AB - 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 A bump emission as compared with bluer (optically flatter) quasars. The change in strength of the 3000 Åbump 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.

KW - Quasars: absorption lines

KW - Quasars: emission lines

KW - Quasars: general

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