期刊
ASTRONOMY & ASTROPHYSICS
卷 510, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200913229
关键词
surveys; galaxies: active
资金
- INAF [PRIN/2007/1.06.10.08]
- ASI [ASI/COFIS/WP3110 I/026/07/0]
- NASA [ADP NNX07AT02G]
- CONACyT [83564]
- ESA Member States
- USA (NASA)
- [175]
- [A-0839]
- [PAPIITIN110209]
Aims. We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The selected sample covers a wide redshift range (0.15 < z < 0.92) and is deeper than any other previous study, encompassing the luminosity range 10(5.5) L-circle dot < L-[OIII] < 10(9.1) L-circle dot. We explore the intrinsic properties of these AGN and the relation to their X-ray emission (derived from the XMM-COSMOS observations). We study their evolution by computing the [OIII]lambda 5007 angstrom line luminosity function (LF) and we constrain the fraction of obscured AGN as a function of luminosity and redshift. Methods. The sample was selected on the basis of the optical emission line ratios, after applying a cut to the signal-to-noise ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams ([O III]/H beta versus [N II]/H alpha and [OIII]/H beta versus [S II]/H alpha) to isolate AGN in the redshift range 0.15 < z < 0.45 and the diagnostic diagram [O III]/H beta versus [O II]/H beta to extend the selection to higher redshift (0.5 < z < 0.92). Results. Combining our sample with one drawn from SDSS, we found that the best description of the evolution of type-2 AGN is a luminosity-dependent density evolution model. Moreover, using the type-1 AGN LF we were able to constrain the fraction of type-2 AGN to the total (type-1 + type-2) AGN population. We found that the type-2 fraction decreases with luminosity, in agreement with the most recent results, and shows signs of a slight increase with redshift. However, the trend with luminosity is visible only after combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the type-2 fraction seems to be quite constant with luminosity.
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