X-ray observations of dust obscured galaxies in the Chandra deep field south

• Published in: Astronomy and astrophysics (Berlin) 2016-08, Vol.592, p.A109
• Main Authors: Corral, A., Georgantopoulos, I., Comastri, A., Ranalli, P., Akylas, A., Salvato, M., Lanzuisi, G., Vignali, C., Koutoulidis, L.
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Dogs; Infrared spectroscopy; infrared: galaxies; Samples; Statistical analysis; Statistical methods; X-rays; X-rays: diffuse background; X-rays: galaxies; X-rays: general; XMM (spacecraft)
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201527624

We present the properties of X-ray detected dust obscured galaxies (DOGs) in the Chandra deep field south. In recent years, it has been proposed that a significant percentage of the elusive Compton-thick (CT) active galactic nuclei (AGN) could be hidden among DOGs. This type of galaxy is characterized by a very high infrared (IR) to optical flux ratio (f24 μm/fR > 1000), which in the case of CT AGN could be due to the suppression of AGN emission by absorption and its subsequent re-emission in the IR. The most reliable way of confirming the CT nature of an AGN is by X-ray spectroscopy. In a previous work, we presented the properties of X-ray detected DOGs by making use of the deepest X-ray observations available at that time, the 2Ms observations of the Chandra deep fields, the Chandra deep field north (CDF-N), and the Chandra deep field south (CDF-S). In that work, we only found a moderate percentage ( 1023 cm-2), whereas 2 look unabsorbed, and the other 3 are only moderately absorbed. Among the highly absorbed AGN, we find that only three could be considered CT AGN. In only one of these three cases, we detect a strong Fe Kα emission line; the source is already classified as a CT AGN with Chandra data in a previous work. Here we confirm its CT nature by combining Chandra and XMM-Newton data. For the other two CT candidates, the non-detection of the line could be because of the low number of counts in their X-ray spectra, but their location in the L2−10 keV/L12 μm plot supports their CT classification. Although a higher number of CT sources could be hidden among the X-ray undetected DOGs, our results indicate that DOGs could be as well composed of only a fraction of CT AGN plus a number of moderate to highly absorbed AGN, as previously suggested. From our study of the X-ray undetected DOGs in the CDF-S, we estimate