Obscured AGN at z ∼ 1 from the zCOSMOS-Bright Survey I. Selection and optical properties of a [Ne v]-selected sample

被引：62

作者：

Mignoli, M. ^{[1
]}

Vignali, C. ^{[2
]}

Gilli, R. ^{[1
]}

Comastri, A. ^{[1
]}

Zamorani, G. ^{[1
]}

Bolzonella, M. ^{[1
]}

Bongiorno, A. ^{[3
]}

Lamareille, F. ^{[4
,5
]}

Nair, P. ^{[1
,6
]}

Pozzetti, L. ^{[1
]}

Lilly, S. J. ^{[7
]}

Carollo, C. M. ^{[7
]}

Contini, T. ^{[4
,5
]}

Kneib, J. -P. ^{[8
]}

Le Fevre, O. ^{[8
]}

Mainieri, V. ^{[9
]}

Renzini, A. ^{[10
]}

Scodeggio, M. ^{[11
]}

Bardelli, S. ^{[1
]}

Caputi, K. ^{[12
]}

Cucciati, O. ^{[13
]}

de la Torre, S. ^{[14
]}

de Ravel, L. ^{[14
]}

Franzetti, P. ^{[11
]}

Garilli, B. ^{[11
]}

Iovino, A. ^{[13
]}

Kampczyk, P. ^{[7
]}

Knobel, C. ^{[7
]}

Kovac, K. ^{[7
]}

Le Borgne, J. -F. ^{[4
,5
]}

Le Brun, V. ^{[8
]}

Maier, C. ^{[7
,15
]}

Pello, R. ^{[4
,5
]}

Peng, Y. ^{[6
]}

Montero, E. Perez ^{[4
,5
]}

Presotto, V. ^{[13
]}

Silverman, J. D. ^{[16
]}

Tanaka, M. ^{[16
]}

Tasca, L. ^{[8
]}

Tresse, L. ^{[8
]}

Vergani, D. ^{[17
]}

Zucca, E.

Bordoloi, R. ^{[7
]}

Cappi, A. ^{[1
]}

Cimatti, A.

Koekemoer, A. M. ^{[6
]}

McCracken, H. J. ^{[18
]}

Moresco, M. ^{[2
]}

Welikala, N. ^{[19
,20
]}

机构：

[1] Osservatorio Astron Bologna, INAF, I-40127 Bologna, Italy

[2] Univ Bologna, Dipartimento Fis & Astron, I-40127 Bologna, Italy

[3] Osserv Astron Roma, INAF, I-00040 Monte Porzio Catone, Italy

[4] CNRS, Inst Rech Astrophys & Planetol, F-31400 Toulouse, France

[5] Univ Toulouse, UPS OMP, IRAP, Toulouse, France

[6] Space Telescope Sci Inst, Baltimore, MD 21218 USA

[7] ETH, Inst Astron, CH-8093 Zurich, Switzerland

[8] Aix Marseille Univ, CNRS, Lab Astrophys Marseille, Marseille, France

[9] European So Observ, Garching, Germany

[10] Osserv Astron Padova, INAF, Padua, Italy

[11] Ist Astrofis Spaziale & Fis Cosm, INAF, Milan, Italy

[12] Univ Groningen, Kapteyn Astron Inst, NL-9700 AV Groningen, Netherlands

[13] Osserv Astron Brera, INAF, Milan, Italy

[14] Royal Observ, Univ Edinburgh, Inst Astron, Edinburgh EH9 3HJ, Midlothian, Scotland

[15] Univ Vienna, Dept Astron, A-1180 Vienna, Austria

[16] Univ Tokyo, Kavli Inst Phys & Math Univ, Kashiwa, Chiba 2778583, Japan

[17] Ist Astrofis Spaziale & Fis Cosm, INAF, Bologna, Italy

[18] Univ Paris 06, Inst Astrophys Paris, F-75014 Paris, France

[19] CNRS, Inst Astrophys Spatiale, F-91405 Orsay, France

[20] Univ Paris Sud XI, F-91405 Orsay, France

来源：

ASTRONOMY & ASTROPHYSICS | 2013年 / 556卷

关键词：

galaxies: active; X-rays: galaxies; SUPERMASSIVE BLACK-HOLES; ACTIVE GALACTIC NUCLEI; DIGITAL-SKY-SURVEY; VLT DEEP SURVEY; STELLAR MASS FUNCTION; X-RAY; LUMINOSITY FUNCTION; REDSHIFT SURVEY; HOST GALAXIES; COSMOS SURVEY;

D O I：

10.1051/0004-6361/201220846

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

Aims. The application of multi-wavelength selection techniques is essential for obtaining a complete and unbiased census of active galactic nuclei (AGN). We present here a method for selecting z similar to 1 obscured AGN from optical spectroscopic surveys. Methods. A sample of 94 narrow-line AGN with 0.65 < z < 1.20 was selected from the 20k-Bright zCOSMOS galaxy sample by detection of the high-ionization [Ne v] lambda 3426 line. The presence of this emission line in a galaxy spectrum is indicative of nuclear activity, although the selection is biased toward low absorbing column densities on narrow-line region or galactic scales. A similar sample of unobscured (type 1 AGN) was collected applying the same analysis to zCOSMOS broad-line objects. This paper presents and compares the optical spectral properties of the two AGN samples. Taking advantage of the large amount of data available in the COSMOS field, the properties of the [Ne v]-selected type 2 AGN were investigated, focusing on their host galaxies, X-ray emission, and optical line-flux ratios. Finally, a previously developed diagnostic, based on the X-ray-to-[Ne v] luminosity ratio, was exploited to search for the more heavily obscured AGN. Results. We found that [Ne v]-selected narrow-line AGN have Seyfert 2-like optical spectra, although their emission line ratios are diluted by a star-forming component. The ACS morphologies and stellar component in the optical spectra indicate a preference for our type 2 AGN to be hosted in early-type spirals with stellar masses greater than 10(9.5-10) M-circle dot, on average higher than those of the galaxy parent sample. The fraction of galaxies hosting [Ne v]-selected obscured AGN increases with the stellar mass, reaching a maximum of about 3% at approximate to 2 x 10(11) M-circle dot. A comparison with other selection techniques at z similar to 1, namely the line-ratio diagnostics and X-ray detections, shows that the detection of the [Ne v] lambda 3426 line is an effective method for selecting AGN in the optical band, in particular the most heavily obscured ones, but cannot provide a complete census of type 2 AGN by itself. Finally, the high fraction of [Ne v]-selected type 2 AGN not detected in medium-deep (approximate to 100-200 ks) Chandra observations (67%) is suggestive of the inclusion of Compton-thick (i.e., with N-H > 10(24) cm(-2)) sources in our sample. The presence of a population of heavily obscured AGN is corroborated by the X-ray-to-[Ne v] ratio; we estimated, by means of an X-ray stacking technique and simulations, that the Compton-thick fraction in our sample of type 2 AGN is 43 +/- 4% (statistical errors only), which agrees well with standard assumptions by XRB synthesis models.

引用

页数：13

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