Optical Spectroscopy Of X-Ray Sources In The Extended Chandra Deep Field South

Date

2009-03

Authors

Treister, Ezequiel
Virani, Shanil
Gawiser, Eric
Urry, C. Megan
Lira, Paulina
Francke, Ilarold
Blanc, Guillermo A.
Cardamone, Carolin N.
Damen, Maaike
Taylor, Edward N.

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Abstract

We present the first results of our optical spectroscopy program aimed to provide redshifts and identifications for the X-ray sources in the Extended Chandra Deep Field South. A total of 339 sources were targeted using the IMACS spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT. We measured redshifts for 186 X-ray sources, including archival data and a literature search. We find that the active galactic nucleus (AGN) host galaxies have on average redder rest-frame optical colors than nonactive galaxies, and that they live mostly in the "green valley." The dependence of the fraction of AGNs that are obscured on both luminosity and redshift is confirmed at high significance and the observed AGN spatial density is compared with the expectations from existing luminosity functions. These AGNs show a significant difference in the mid-IR to X-ray flux ratio for obscured and unobscured AGNs, which can be explained by the effects of dust self-absorption on the former. This difference is larger for lower luminosity sources, which is consistent with the dust opening angle depending on AGN luminosity.

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Citation

Treister, Ezequiel, Shanil Virani, Eric Gawiser, C. Megan Urry, Paulina Lira, Harold Francke, Guillermo A. Blanc et al. "Optical spectroscopy of X-ray sources in the extended Chandra deep field south." The Astrophysical Journal, Vol. 693, No. 2 (Mar., 2009): 1713.