TY - JOUR
T1 - Optical and infrared properties of active galactic nuclei in the Lockman Hole
AU - Rovilos, E.
AU - Fotopoulou, S.
AU - Salvato, M.
AU - Burwitz, V.
AU - Egami, E.
AU - Hasinger, G.
AU - Szokoly, G.
N1 - Funding Information:
G.H. and M.S acknowledge support by the German Deutsche Forschungsgemeinschaft, DFG Leibniz Prize (FKZ HA 1850/28-1). We thank M. Brusa for reading the manuscript and providing useful comments.
PY - 2011
Y1 - 2011
N2 - We present the observed-frame optical, near-, and mid-infrared properties of X-ray-selected active galactic nuclei (AGN) in the Lockman Hole. Using a likelihood ratio method on optical, near-infrared or mid-infrared catalogues, we assigned counterparts to 401 out of the 409 X-ray sources of the XMM-Newton catalogue. Accurate photometry was collected for all the sources from U to 24 μm. We used X-ray and optical criteria to remove any normal galaxies, galactic stars, or X-ray clusters among them and studied the multi-wavelength properties of the remaining 377 AGN. We used a mid-IR colour-colour selection to understand the AGN contribution to the optical and infrared emission. Using this selection, we identified different behaviours of AGN-dominated and host-dominated sources in X-ray-optical-infrared colour-colour diagrams. More specifically, the AGN-dominated sources show a clear trend in the f x/fRC vs. RC - K and f24 μm /fRC vs. RC - K diagrams, while the hosts follow the behaviour of non X-ray detected galaxies. In the optical-near- infrared colour-magnitude diagram we see that the known trend of redder objects to be more obscured in X-rays is stronger for AGN-dominated than for host-dominated systems. This is an indication that the trend is more related to the AGN, which contaminate the overall colours, than to any evolutionary effects. Finally, we find that a significant fraction (∼30%) of the reddest AGN are not obscured in X-rays.
AB - We present the observed-frame optical, near-, and mid-infrared properties of X-ray-selected active galactic nuclei (AGN) in the Lockman Hole. Using a likelihood ratio method on optical, near-infrared or mid-infrared catalogues, we assigned counterparts to 401 out of the 409 X-ray sources of the XMM-Newton catalogue. Accurate photometry was collected for all the sources from U to 24 μm. We used X-ray and optical criteria to remove any normal galaxies, galactic stars, or X-ray clusters among them and studied the multi-wavelength properties of the remaining 377 AGN. We used a mid-IR colour-colour selection to understand the AGN contribution to the optical and infrared emission. Using this selection, we identified different behaviours of AGN-dominated and host-dominated sources in X-ray-optical-infrared colour-colour diagrams. More specifically, the AGN-dominated sources show a clear trend in the f x/fRC vs. RC - K and f24 μm /fRC vs. RC - K diagrams, while the hosts follow the behaviour of non X-ray detected galaxies. In the optical-near- infrared colour-magnitude diagram we see that the known trend of redder objects to be more obscured in X-rays is stronger for AGN-dominated than for host-dominated systems. This is an indication that the trend is more related to the AGN, which contaminate the overall colours, than to any evolutionary effects. Finally, we find that a significant fraction (∼30%) of the reddest AGN are not obscured in X-rays.
KW - Galaxies: Seyfert
KW - Galaxies: active
KW - Galaxies: statistics
KW - Infrared: galaxies
KW - X-rays: galaxies
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U2 - 10.1051/0004-6361/201015763
DO - 10.1051/0004-6361/201015763
M3 - Article
AN - SCOPUS:79955037669
VL - 529
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
SN - 0004-6361
M1 - A135
ER -