期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 462, 期 2, 页码 1826-1833出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stw1742
关键词
galaxies: active; galaxies: statistics; galaxies: stellar content
资金
- FAPESC
- CAPES
- CNPq
- CAPES CsF-PVE project [88881.068116/2014-01]
- France-Brazil CAPES-COFECUB programme
- Observatory de Paris
- National Aeronautics and Space Administration
- Alfred P. Sloan Foundation
- National Science Foundation
- US Department of Energy
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- American Museum of Natural History
- Astrophysical Institute Potsdam
- University of Basel
- University of Cambridge
- Case Western Reserve University
- University of Chicago
- Drexel University
- Fermilab
- Institute for Advanced Study
- Japan Participation Group
- Johns Hopkins University
- Joint Institute for Nuclear Astrophysics
- Kavli Institute for Particle Astrophysics and Cosmology
- Korean Scientist Group
- Chinese Academy of Sciences (LAMOST)
- Los Alamos National Laboratory
- Max-Planck-Institute for Astronomy (MPIA)
- Max-Planck-Institute for Astrophysics (MPA)
- New Mexico State University
- Ohio State University
- University of Pittsburgh
- University of Portsmouth
- Princeton University
- United States Naval Observatory
- University of Washington
We use the Sloan Digital Sky Survey (SDSS) and Wide-field Sky Survey Explorer surveys to investigate the real nature of galaxies defined as low-ionization nuclear emission-line regions (LINERs) in the BPT diagram. After establishing a mid-infrared colour W2-W3 = 2.5 as the optimal separator between galaxies with and without star formation, we investigate the loci of different galaxy classes in the W-H alpha versus W2-W3 space. We find that: (1) a large fraction of LINER-like galaxies are emission-line retired galaxies, i.e. galaxies which have stopped forming stars and are powered by hot low-mass evolved stars (HOLMES). Their W2-W3 colours show no sign of star formation and their Ha equivalent widths, W-H alpha, are consistent with ionization by their old stellar populations. (2) Another important fraction have W2-W3 indicative of star formation. This includes objects located in the supposedly 'pure AGN' zone of the BPT diagram. (3) A smaller fraction of LINER-like galaxies have no trace of star formation from W2-W3 and a high W-H alpha, pointing to the presence of an AGN. (4) Finally, a few LINERs tagged as retired by their W-H alpha but with W2-W3 values indicative of star formation are late-type galaxies whose SDSS spectra cover only the old 'retired' bulge. This reinforces the view that LINER-like galaxies are a mixed bag of objects involving different physical phenomena and observational effects thrusted into the same locus of the BPT diagram.
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