Spectroscopic Identification of Type 2 Quasars at Z < 1 in SDSS-III/BOSS

TL;DR

This study presents a large spectroscopic sample of 2758 type 2 quasars at z ≤ 1 from SDSS-III/BOSS, analyzing their emission-line properties, demographics, and infrared counterparts to improve understanding of their physical nature and evolution.

Contribution

The paper introduces a new, extensive sample of type 2 quasars selected via emission-line diagnostics, including many with previously mismeasured redshifts, and provides detailed spectral decompositions and line profile analyses.

Findings

Over 400 quasars had incorrect redshifts in the database.

Majority have infrared counterparts with median luminosity 4.2 x 10^44 erg/sec.

Only 34% would be identified by infrared color cuts.

Abstract

The physics and demographics of type 2 quasars remain poorly understood, and new samples of such objects selected in a variety of ways can give insight into their physical properties, evolution, and relationship to their host galaxies. We present a sample of 2758 type 2 quasars at z $\leq$ 1 from the SDSS-III/BOSS spectroscopic database, selected on the basis of their emission-line properties. We probe the luminous end of the population by requiring the rest-frame equivalent width of [OIII] to be > 100 {\AA}. We distinguish our objects from star-forming galaxies and type 1 quasars using line widths, standard emission line ratio diagnostic diagrams at z < 0.52 and detection of [Ne V]{\lambda}3426{\AA} at z > 0.52. The majority of our objects have [OIII] luminosities in the range 10^8.5-10^10 L$_{\odot}$ and redshifts between 0.4 and 0.65. Our sample includes over 400 type 2 quasars with incorrectly measured redshifts in the BOSS database; such objects often show kinematic substructure or outflows in the [OIII] line. The majority of the sample has counterparts in the WISE survey, with median infrared luminosity {\nu}L{\nu}[12{\mu}m] = 4.2 x 10^44 erg/sec. Only 34 per cent of the newly identified type 2 quasars would be selected by infrared color cuts designed to identify obscured active nuclei, highlighting the difficulty of identifying complete samples of type 2 quasars. We make public the multi-Gaussian decompositions of all [OIII] profiles for the new sample and for 568 type 2 quasars from SDSS I/II, together with non-parametric measures of line profile shapes and identify over 600 candidate double-peaked [OIII] profiles.