2007A&A...470..557C


Query : 2007A&A...470..557C

2007A&A...470..557C - Astronomy and Astrophysics, volume 470, 557-570 (2007/8-1)

Elusive AGN in the XMM-Newton bright serendipitous survey.

CACCIANIGA A., SEVERGNINI P., DELLA CECA R., MACCACARO T., CARRERA F.J. and PAGE M.J.

Abstract (from CDS):

Optical follow-up of X-ray selected sources finds a significant fraction of ``optically dull'' sources characterized by optical spectra without obvious signature of AGN activity. In many cases, however, the presence of an AGN is inferred from other diagnostics (e.g. the X-ray properties). Understanding and accounting for this ``elusiveness'' is mandatory for a reliable study of the AGN physical and statistical properties. We investigate here the nature of all the sources (35 in total) in the XMM-Newton bright serendipitous survey (which is 86% optically identified) showing an optical spectrum dominated by the light from the host galaxy with no evidence (or little evidence) for the presence of an AGN. We use the X-ray spectral analysis to assess the presence of an AGN in these sources and to characterize its properties. We detect AGN activity in 33 out of 35 sources. The remaining 2 sources are the ones with the lowest X-ray luminosity in the sample (L_[2-10 keV]_<1041erg/s) and their X-ray emission could be produced within the host galaxy. We find that the ``recognition problem'' for AGN is very critical in the low-luminosity regime (at least 60% of the AGN with L_[2-10 keV]_<1043erg/s are elusive) becoming negligible for high X-ray luminosities (∼1.5% of elusive AGN with L_[2-10 keV]_>1044erg/s). This problem affects mostly absorbed AGN (∼40% of type 2 AGN in the survey are elusive) but also a significant fraction of unabsorbed AGN (8%). We find that the simplest explanations of why these 33 (or most of them) AGNs are elusive are two: at low X-ray luminosities (<1043erg/s) the most important reason is the intrinsically low AGN/galaxy contrast (optical dilution) while at high luminosities (>1044erg/s) it is due to the optical absorption (in the Compton-thin regime, i.e. NH<1024cm–2). Alternative hypotheses, like the presence of Compton-thick sources, BL Lac objects or ``non-standard'' AGN (e.g. with αOX<1 or with weak/absorbed Narrow Line Region) are not supported by the data although we cannot exclude the presence in the sample of a few sources of these types.

Abstract Copyright:

Journal keyword(s): galaxies: active - galaxies: nuclei - X-ray: galaxies - surveys

Simbad objects: 35

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Number of rows : 35
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 2MASS J00053278+2007176 QSO 00 05 32.8412340264 +20 07 17.394483576           ~ 12 0
2 2MASS J01254036+0157534 AGN 01 25 40.3629187392 +01 57 53.539485804           ~ 7 0
3 IC 115 AGN 01 26 54.4300162320 +19 12 52.190971380   15.2       ~ 73 1
4 2XMM J013943.5-674908 Sy1 01 39 43.8 -67 49 09   18.47 16.70 17.40   ~ 11 0
5 2XMM J014109.5-675638 AGN 01 41 09.5 -67 56 38   20.76   19.08   ~ 8 0
6 2XMM J014227.2+133452 AGN 01 42 27.286 +13 34 52.95           ~ 7 0
7 LEDA 1049275 AGN 02 18 22.1650924776 -05 06 14.252224752   16.4753 15.7476 10.80   ~ 29 0
8 2XMM J025645.3+000032 AGN 02 56 45.3236133696 +00 00 33.349693572           ~ 7 0
9 2MASX J03185940-4416257 GiC 03 18 59.4613011120 -44 16 26.242170240     15.90     ~ 14 0
10 2MASS J04344774-7753284 AGN 04 34 47.7322565472 -77 53 28.282725096           ~ 6 0
11 2XMM J050453.3-284531 AGN 05 04 53.3 -28 45 30   20.53   18.94   ~ 7 0
12 2MASX J05182245+7932096 AGN 05 18 22.3126878936 +79 32 10.010430996           ~ 7 0
13 XBS J052116.2-252957 AGN 05 21 16.1 -25 29 58           ~ 6 0
14 XBS J052128.9-253032 AGN 05 21 29.0 -25 30 32       20.69   ~ 6 0
15 [VV2010c] J075117.9+180856 AGN 07 51 17.9 +18 08 56           ~ 8 0
16 2MASS J08373700+2551521 AGN 08 37 37.0067161968 +25 51 52.054397064           ~ 8 0
17 XBS J090729.1+620824 AGN 09 07 29.3 +62 08 27           ~ 5 0
18 2MASS J09452626-0850061 AGN 09 45 26.2615218792 -08 50 05.836533036           ~ 6 0
19 2XMM J100032.1+553630 Sy2 10 00 32.2408996752 +55 36 30.938883156   19.99 19.37     ~ 23 0
20 2MASX J10184307+4135163 Sy2 10 18 43.1368311024 +41 35 16.232566056   16.87 16.31     ~ 16 0
21 [VV2006] J111654.8+180304 QSO 11 16 54.7 +18 03 06   13.84 12.76     ~ 466 0
22 2MASS J11202664+4315185 Sy2 11 20 26.6419160928 +43 15 18.460850220           ~ 10 0
23 NGC 4291 GiG 12 20 17.699 +75 22 15.47   17.0       ~ 304 1
24 2MASS J13394242-3150034 AGN 13 39 42.4354406040 -31 50 03.386660136   17.79   16.69 16.23 ~ 7 0
25 2MASS J13465688+5803155 QSO 13 46 56.88 +58 03 15.6           ~ 9 0
26 2XMM J140059.9-110940 AGN 14 00 59.9169080688 -11 09 40.985973252       18.80   ~ 8 0
27 2MASS J14274165+4233380 AGN 14 27 41.6460286536 +42 33 38.118997440           ~ 7 0
28 XBS J143835.1+642928 AGN 14 38 34.7 +64 29 30           ~ 5 0
29 2MASS J14391072+6405291 BL? 14 39 10.7366721888 +64 05 28.941292500           ~ 6 0
30 2XMM J161820.8+124115 AGN 16 18 20.795 +12 41 15.22           ~ 6 0
31 2MASS J16333186+5705204 QSO 16 33 31.8825750600 +57 05 20.275436436           ~ 10 0
32 2MASS J19324853-7233532 AGN 19 32 48.5520156840 -72 33 53.363806056           ~ 8 0
33 2MASX J23040125+0315191 AGN 23 04 01.2451920744 +03 15 19.009455660   13.2       ~ 14 0
34 2MASS J23043416+1227269 AGN 23 04 34.1465363448 +12 27 26.868625920           ~ 6 0
35 ESO 148-2 Sy2 23 15 46.772 -59 03 15.94   14.94 14.73 13.95   ~ 265 1

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