期刊
ASTRONOMY & ASTROPHYSICS
卷 531, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201016143
关键词
galaxies: active; galaxies: high-redshift; galaxies: Seyfert; galaxies: fundamental parameters
资金
- La cite de l'espace
- Alfred P. Sloan Foundation
- National Science Foundation
- US Department of Energy
- National Aeronautics and Space Administration
- 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
Aims. In this paper we present a classification of emission-line galaxies at intermediate and high redshifts (0.5 less than or similar to z less than or similar to 1.0 for optical spectra, z greater than or similar to 2.5 for near-infrared spectra), using the D-n(4000) index as a supplementary diagnostic. Our goal is to complement the diagnostic based only on emission-line ratios from the blue part of the spectra, which suffer from some limitations for the classification of Seyfert 2 and composite galaxies. Methods. We used a sample of 89 379 galaxies with a good signal-to-noise ratio from the Sloan Digital Sky Survey (data release 7). Using the classification scheme presented in Paper I, we classified these galaxies with a diagnostic diagram involving the [OIII]lambda 5007/H beta and [OII]lambda lambda 3726 + 3729/H beta emission-line ratios. Then we derived a supplementary diagnostic involving D-n(4000) to improve this classification, in the regions where objects of different types are mixed. To show the validity of our spectral classification we established success-rate and contamination charts, then we compared our results to those obtained with the reference classification scheme that was obtained also using H alpha, [NII]lambda 6584, and [SII]lambda lambda 6717 + 6731 emission lines. Results. We show that our supplementary classification based on the D-n(4000) index allows to separate unambiguously star-forming galaxies from Seyfert 2 in the region where they were mixed in Paper I. It also significantly reduces the region where star-forming galaxies are mixed with composites.
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