期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 453, 期 4, 页码 3932-3952出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv1710
关键词
surveys; galaxies: evolution; quasars: general; infrared: galaxies
资金
- Alfred P. Sloan Foundation
- National Science Foundation
- U.S. Department of Energy
- University of Arizona
- Brazilian Participation Group
- Brookhaven National Laboratory
- University of Cambridge
- University of Florida
- French Participation Group
- German Participation Group
- Instituto de Astrofisica de Canarias
- Michigan State/Notre Dame/JINA Participation Group
- Johns Hopkins University
- Lawrence Berkeley National Laboratory
- Max Planck Institute for Astrophysics
- New Mexico State University
- New York University
- Ohio State University
- Pennsylvania State University
- University of Portsmouth
- Princeton University
- Spanish Participation Group
- University of Tokyo
- University of Utah
- Vanderbilt University
- University of Virginia
- University of Washington
- Yale University
- National Aeronautics and Space Administration
- NASA
- Hubble grant [HST-GO-13014.06]
- USA National Science Foundation [AST-1009628]
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1516784] Funding Source: National Science Foundation
- Science and Technology Facilities Council [ST/L00481X/1] Funding Source: researchfish
- STFC [ST/L00481X/1] Funding Source: UKRI
Quasars with extremely red infrared-to-optical colours are an interesting population that can test ideas about quasar evolution as well as orientation, obscuration and geometric effects in the so-called AGN unified model. To identify such a population, we match the quasar catalogues of the Sloan Digital Sky Survey (SDSS), the Baryon Oscillation Spectroscopic Survey (BOSS) to the Wide-Field Infrared Survey Explorer (WISE) to identify quasars with extremely high infrared-to-optical ratios. We identify 65 objects with r(AB) -W4(Vega) > 14 mag (i. e. F-v (22 mu m)/F-v (r) greater than or similar to 1000). This sample spans a redshift range of 0.28 < z < 4.36 and has a bimodal distribution, with peaks at z similar to 0.8 and z similar to 2.5. It includes three z > 2.6 objects that are detected in the W4 band but not W1 or W2 (i. e. 'W1W2 dropouts'). The SDSS/BOSS spectra show that the majority of the objects are reddened type 1 quasars, type 2 quasars (both at low and high redshift) or objects with deep low-ionization broad absorption lines (BALs) that suppress the observed r-band flux. In addition, we identify a class of type 1 permitted broad emission-line objects at z similar or equal to 2-3 which are characterized by emission line rest-frame equivalent widths (REWs) of greater than or similar to 150 angstrom, much larger than those of typical quasars. In particular, 55 per cent (45 per cent) of the non-BAL type 1s with measurable CIV in our sample have REW(C IV) > 100 (150)angstrom, compared to only 5.8 per cent (1.3 per cent) for non-BAL quasars in BOSS. These objects often also have unusual line ratios, such as very high NV/Ly alpha ratios. These large REWs might be caused by suppressed continuum emission analogous to type 2 quasars; however, there is no obvious mechanism in standard unified models to suppress the continuum without also obscuring the broad emission lines.
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