Please use this identifier to cite or link to this item:
http://hdl.handle.net/20.500.12386/34663
Title: | A new technique to efficiently select Compton-thick AGN | Authors: | SEVERGNINI, Paola CACCIANIGA, Alessandro DELLA CECA, Roberto |
Issue Date: | 2012 | Journal: | ASTRONOMY & ASTROPHYSICS | Number: | 542 | First Page: | A46 | Abstract: | Aims: We present a new efficient diagnostic method, based on mid-infrared and X-ray data, to select local (z < 0.1) Compton-thick AGN with the aim of estimating their surface and space density. Methods: We define a region in the X-ray-to-mid-IR [F(2-12 keV)/F25ν25] vs. X-ray color (HR) plane associated to Compton-thick AGN, i.e. [F(2-12 keV)/F25ν25] < 0.02 and HR > - 0.2. On the basis of this selection method we build up a sample of 43 Compton-thick AGN candidates using data from IRAS Point Source and 2XMM-Newton catalogues. In order to test the efficiency of the proposed method in selecting Compton-thick AGN we use the results of the X-ray spectral analysis performed on all the sources of our sample (presented in a parallel work). After taking into account the different selection effects, we have estimated the number of Compton-thick in the local Universe and their density down to the IRAS flux limit of F25 = 0.5 Jy. Results: We find that the diagnostic plot proposed here is an efficient method to select Compton-thick AGN in the nearby Universe since ~84% of the sources populating the proposed Compton-thick region are actually Compton-thick AGN. Twenty percent are newly-discovered Compton-thick AGN. We then estimate the surface density of Compton-thick AGN down to the IRAS PSC catalogue flux limit (F25 = 0.5 Jy) that turns out to be ρCT ~ 3 × 10-3 src deg-2. After estimating an equivalent IR-to-hard-X-ray limiting flux, we compare our result with those found with Swift-BAT. We find that the surface density derived here is a factor 4 above the density computed in the hard X-ray surveys. This difference is ascribed, at least in part, to a significant contribution (~60-90%) of the star-forming activity to the total 25 μm emission for the sources in our sample. By considering only the 25 μm AGN emission, we estimate a surface density of Compton-thick AGN which is consistent with the results found by hard X-ray surveys. Finally, we estimated the co-moving space density of Compton-thick AGN with intrinsic LX > 1043 erg s-1 (0.004 < z < 0.06): ΦC-thick ~ (3.5-0.5+4.5)×10-6 Mpc-3. The prediction for Compton-thick AGN based on the synthesis model of X-ray background in Gilli et al. (2007) is consistent with this value. | URI: | http://hdl.handle.net/20.500.12386/34663 | URL: | http://arxiv.org/abs/1204.4359v1 https://www.aanda.org/articles/aa/full_html/2012/06/aa18417-11/aa18417-11.html |
ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/201118417 | Bibcode ADS: | 2012A&A...542A..46S | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
Files in This Item:
File | Description | Size | Format | |
---|---|---|---|---|
AA_2012_542_A46.pdf | PDF editoriale | 286.51 kB | Adobe PDF | View/Open |
Page view(s)
61
checked on Feb 17, 2025
Download(s)
11
checked on Feb 17, 2025
Google ScholarTM
Check
Altmetric
Altmetric
Items in DSpace are published in Open Access, unless otherwise indicated.