X-ray and Infrared Diagnostics of Star Formation and Black Hole Accretion in Galaxies
AuthorRigby, Jane Rebecca
AdvisorRieke, George H
Committee ChairRieke, George H
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractUsing infrared and X-ray diagnostics, we study star--formation and black hole accretion in nearby and distant galaxies.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 micron/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 micron) 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 micron 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 micron 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.