Bibcode
Cepa, J.; Bongiovanni, A.; Pérez-García, A. M. ; Sánchez-Portal, M.; Pović, M.
Bibliographical reference
Feeding Compact Objects: Accretion on All Scales, Proceedings of the International Astronomical Union, IAU Symposium, Volume 290, pp. 295-296
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2
2013
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Description
The connection between active galactic nuclei (AGN) and their hosts
showed to be important for understanding the formation and evolution of
active galaxies. Using X-ray and deep optical data, we study how
morphology and colours are related to X-ray properties at redshifts
z<=2.0 for a sample of > 300 X-ray detected AGN in the
Subaru/XMM-Newton Deep Survey (SXDS; Furusawa et al. 2008) and
Groth-Westphal Strip (GWS; Pović et al. 2009) fields. We
performed our morphological classification using the galSVM code
(Huertas-Company et al. 2008), which is a new method that is
particularly suited when dealing with high-redshift sources. To separate
objects between X-ray unobscured and obscured, we used X-ray hardness
ratio HR(0.5-2 keV/2-4.5 keV). Colour-magnitude diagrams were studied in
relationship to redshift, morphology, X-ray obscuration, and
X-ray-to-optical flux ratio. Around 50% of X-ray detected AGN at
z<=2.0 analysed in this work reside in spheroidal and bulge-dominated
galaxies, while at least 18% have disk-dominated hosts. This suggests
that different mechanisms may be responsible for triggering the nuclear
activity. When analysing populations of X-ray detected AGN in both
colour-magnitude (CMD) and colour-stellar mass diagrams (Figure 1), the
highest number of sources is found to reside in the green valley at
redshifts ~ 0.5-1.5. For the first time we studied CMD of these AGN in
relation to morphology and X-ray obscuration, finding that they can
reside in both early- and late-type hosts, where both morphological
types cover similar ranges of X-ray obscuration (Figure 1). Our findings
appear to confirm some previous suggestions that X-ray selected AGN
residing in the green valley represent a transitional population (e.g.
Nandra et al. 2007, Silverman et al. 2008, Treister et al. 2009),
quenching star formation by means of different AGN feedback mechanisms
and evolving to red-sequence galaxies. More details on analysis and
results presented here can be found in Pović et al. 2012.