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Extremely red quasars in BOSS
Journal article   Open access

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, …
Monthly notices of the Royal Astronomical Society, v 464(3), pp 3431-3463
01 Jan 2017
url
https://doi.org/10.1093/mnras/stw2387View
Published, Version of Record (VoR)Maybe Open Access (Publisher Bronze) Open

Abstract

Astronomy & Astrophysics Physical Sciences Science & Technology
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/L-y alpha, N-V/C (IV), Si (IV)/C (IV) and other flux ratios, and very broad and blueshifted [O (III)]lambda 5007. 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 angstrom 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)) similar to 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.

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Astronomy & Astrophysics
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