Extremely red quasars in BOSS

Fred Hamann, Nadia L. Zakamska, Nicholas Ross, Isabelle Paris, Rachael M. Alexandroff, Carolin Villforth, Gordon T. Richards, Hanna Herbst, W. Niel Brandt, Ben Cook, Kelly D. Denney, Jenny E. Greene, Donald P. Schneider, Michael A. Strauss

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


Red quasars are candidate young objects in an early transition stage of massive galaxy evolution. Our team recently discovered a population of extremely red quasars (ERQs) in the Baryon Oscillation Spectroscopic Survey (BOSS) that has a suite of peculiar emission-line properties including large rest equivalent widths (REWs), unusual 'wingless' line profiles, large N V/Lyα, N V/C IV, Si IV/C IV and other flux ratios, and very broad and blueshifted [O III] λ5007. Here we present a new catalogue of C IV and N V emission-line data for 216 188 BOSS quasars to characterize the ERQ line properties further. We show that they depend sharply on UV-to-mid-IR colour, secondarily on REW(C IV), and not at all on luminosity or the Baldwin Effect. We identify a 'core' sample of 97 ERQs with nearly uniform peculiar properties selected via i-W3 ≥ 4.6 (AB) and REW(C IV) ≥ 100 Å at redshifts 2.0-3.4. A broader search finds 235 more red quasars with similar unusual characteristics. The core ERQs have median luminosity (log L(ergs s−1) ∼ 47.1, sky density 0.010 deg−2, surprisingly flat/blue UV spectra given their red UV-to-mid-IR colours, and common outflow signatures including BALs or BAL-like features and large C IV emission-line blueshifts. Their SEDs and line properties are inconsistent with normal quasars behind a dust reddening screen. We argue that the core ERQs are a unique obscured quasar population with extreme physical conditions related to powerful outflows across the line-forming regions. Patchy obscuration by small dusty clouds could produce the observed UV extinctions without substantial UV reddening.

Original languageEnglish (US)
Pages (from-to)3431-3463
Number of pages33
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jan 1 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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