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| Title: | X-ray and infrared diagnostics of star formation and black hole accretion in galaxies | |
| Authors: | Rigby, Jane Rebecca | |
| Affiliation: | The University of Arizona, United States -- Arizona | |
| Publication: | PhD dissertation, Proquest Dissertations And Theses 2006. Section 0009, Part 0606 207 pages; [Ph.D. dissertation].United States -- Arizona: The University of Arizona; 2006. Publication Number: AAT 3205368. DAI-B 67/01, Jul 2006 | |
| Publication Date: | 06/2006 | |
| Origin: | UMI | |
| Keywords: | X-ray, Infrared diagnostics, Star formation, Black hole, Accretion, Galaxies | |
| Comment: | Publication Number: AAT 3205368; ISBN: | |
| Bibliographic Code: | 2006PhDT.........2R |
We examine diagnostics of the hardness of the ionizing field in low-redshift starburst galaxies, to constrain the initial mass function. We obtain new measurements of HeI 1.7 mm/Br 10, a physically simple diagnostic, then test ISO mid-infrared line ratios, finding them reliable. Compared to new photoionization models, the ISO ratios in 27 nearby starburst galaxies are systematically low. This argues that solar-metallicity starbursts are deficient in massive stars, or that such stars are present but highly embedded.
Using Spitzer, HST, Chandra, and ground-based data, we examine the multi- wavelength (0.4--24 mm) spectral energy distributions and X-ray properties of X-ray-selected active galactic nuclei (AGN) in several deep fields: the Chandra Deep Field South, the Lockman Hole, and the extended Groth Strip. We examine the 24 mm to X-ray flux and luminosity ratios for 157 AGN at z ~ 1; the luminosity ratios have not strongly evolved since z ~ 0, and we find no trend with X-ray column density. This means that highly-obscured AGN do not have exceptional infrared fluxes. We examine the SEDs of 45 bright X-ray and 24 mm sources: only 22% are classified as unobscured "type 1" AGN; 18% are classified as ULIRG-like SEDs; and the majority are classified as obscured ("type 2") AGN or spiral-like SEDs. This supports the picture from X-ray surveys that much of the AGN activity in the distant universe is significantly obscured. We examine why 20% of X-ray-selected AGN are optically-faint; they lie at significantly higher redshifts (median z = 1.6) than most X-ray-selected AGN, and their spectra are intrinsically red. Their contribution to the X-ray Seyfert luminosity function is comparable to that of optically-bright AGN at z > 1, but they do not significantly alter the redshift distribution. Lastly, we investigate why half of X-ray-selected AGN lack signs of accretion in optical spectra. We find that these "optically-dull" AGN have Seyfert like mid-infrared emission, which argues that they do not have abnormally-weak UV/optical continua. The axis ratios of their host galaxies argue that extinction by host galaxies plays a key role in hiding nuclear emission lines.
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