Physical properties of the CDFS X-ray sources through fitting spectral energy distributions

Abstract

ABSTRACT The physical parameters of galaxies and/or active galactic nucleus (AGNs) can be derived by fitting their multiband spectral energy distributions (SEDs). By using cigale code, we perform multiband SED fitting (from ultraviolet to infrared) for 791 X-ray sources (518 AGNs and 273 normal galaxies) in the 7 Ms Chandra Deep Field-south survey (CDFS). We consider the contributions from AGNs and adopt more accurate redshifts than published before. Therefore, more accurate star formation rates (SFRs) and stellar masses (M*) are derived. We classify the 518 AGNs into type-I and type-II based on their optical spectra and their SEDs. Moreover, six AGN candidates are selected from the 273 normal galaxies based on their SEDs. Our main results are as follows: (1) the host galaxies of AGNs have larger M* than normal galaxies, implying that AGNs prefer to host in massive galaxies; (2) the specific star formation rates (sSFRs) of AGN host galaxies are different from those of normal galaxies, suggesting that AGN feedback may play an important role in the star formation activity; (3) we find that the fraction of optically obscured AGNs in CDFS decreases with the increase of intrinsic X-ray luminosity, which is consistent with previous studies; and (4) the host galaxies of type-I AGNs tend to have lower M* than type-II AGNs, which may suggest that dust in the host galaxy may also contribute to the optical obscuration of AGNs.