A MINI X-RAY SURVEY OF SUB-DAMPED LYMAN-ALPHA ABSORPTION SYSTEMS: SEARCHING FOR ACTIVE GALACTIC NUCLEI FORMED IN PROTOGALAXIES
- Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424 (United States)
A significant fraction of the sub-damped Lyman-alpha (sub-DLA) absorption systems in quasar spectra appear to be metal-rich, including many with even super-solar element abundances. This raises the question whether some sub-DLAs may harbor active galactic nuclei (AGNs), since supersolar metallicities are observed in AGNs. Here, we investigate this question based on a mini-survey of 21 quasars known to contain sub-DLAs in their spectra. The X-ray observations were performed with the Chandra X-ray Observatory. In cases of no detection, we estimated upper limits for the X-ray luminosities of possible AGNs at the redshifts of the sub-DLAs. In six cases, we find possible X-ray emission within ∼1'' of the background quasar, which is consistent with the presence of a nearby X-ray source. If these nearby X-ray sources are at the redshifts of the sub-DLAs, then their estimated 0.2-10 keV luminosities range between 0.8 × 10{sup 44} h {sup –2} and 4.2 × 10{sup 44} h {sup –2} erg s{sup –1}, thus ruling out a normal late-type galaxy origin, and suggesting that the emission originates in a galactic nucleus near the center of a protogalaxy. The projected distances of these possible nearby X-ray sources from the background quasars lie in the range of 3-7 h {sup –1} kpc, which is consistent with our hypothesis that they represent AGNs centered on the sub-DLAs. Deeper follow-up X-ray and optical observations are required to confirm the marginal detections of X-rays from these sub-DLA galaxies.
- OSTI ID:
- 22270859
- Journal Information:
- Astrophysical Journal, Vol. 775, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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