X-ray view of obscured AGN and its connection with galaxy evolution
Abstract
Active Galactic Nuclei (AGN) and starburst are two intense and competitive energy releasing phenomena occurring at the centers of active galaxies, and both are often buried by dust and gas. Penetrating the heavy obscuration using X-rays is an efficient tool for probing the galactic centers. To determine the intrinsic obscuration of Type 2 AGNs (where line of sight is intercepted by the obscuring torus) and the fraction of Compton-thick AGN (NH>10^24 cm-2), we have studied the archival X-ray data for a sizable sample of Type 2 AGN selected based on their [O III] optical emission lines, which servers as an intrinsic AGN flux proxy. Our results indicate that the majority of the sample are heavily obscured, and the obscuration obtained from the simple spectral fits is under-predicted. Using OIII and Fe Kα emission lines as the intrinsic luminosity indicators and compared with local Seyfert 2s, we find that high AGN luminosities are not strongly impacting the obscuration present in obscured AGN. We also study the X-ray emission from a rare sample of local Lyman Break Analogs (LBAs), which are believed to be AGN/starburst composites based on their optical emission lines. We find X-ray luminosities of order 10^42 erg/s and ratios of X-ray to far-IR luminosities that are higher than values in pure starburst galaxies by factor of about 10, which strongly suggests the presence of an AGN in at least some of these galaxies. By investigating a starburst merging galaxy which also hosts a Compton-thick AGN, we are also exploring the relative contribution to the X-ray luminosity by both AGN and starburst. Our work provides an X-ray view on obscured AGNs, starburst galaxies and the composite galaxies, which helps to understand the co-evolution of galaxies and black holes.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 2012
- Bibcode:
- 2012PhDT.......130J