The Environments of Obscured Quasars
Jones, Kristen, Astronomy - Graduate School of Arts and Sciences, University of Virginia
Evans, Aaron, Department of Astronomy, University of Virginia
Whittle, D, Department of Astronomy, University of Virginia
The study of Active Galactic Nuclei (AGN) hinges on observations that probe the underlying characteristics of the supermassive black hole and the host galaxy in which it is found. Traditional identification of an AGN has relied on broad emission lines and high UV/optical luminosities. In the past fifteen years, infrared (IR) observations have revealed an AGN population that is shrouded in dust and demonstrated that such a population makes up a significant (at least 50%) contribution of the total AGN population. It is therefore vital that future work on all types of AGN be designed to include both obscured and normal or unobscured objects in their samples.
With this in mind, this dissertation explores the environments associated with dust-obscured luminous objects, particularly Luminous Infrared Galaxies (LIRGs) and Type 1 and Type 2 quasars. The environment at all scales (from the nuclear (<1pc) to the halo (10s to 100s of Mpc)) plays a role not only in creating AGN but in how they and their host galaxies evolve with time to become (or be observed as) vastly different populations. This makes it a challenging field to explore, but one with many avenues open to investigation.
First, I reveal the complexities involved in the 1-2 kpc (circumnuclear) environment scale of LIRGs, objects where AGN and star formation processes can both play an equivalent role. Mid-infrared high resolution images reveal diverse morphology that suggests the importance of star formation in this scale in powering LIRG luminosity and channeling gas into the nuclear (<100pc) region. I identify a circumnuclear spiral within an elliptical galaxy, as well as possible disky structures in another two objects. The final two objects appear to be unresolved. I find the circumnuclear region emits a dominant proportion of the total LIRG luminosity for the majority of the objects in the sample, with minimum surface brightness densities on order of 10^10 L_solar kpc^−2, approaching the surface brightness densities found in star forming regions in other galaxies.
Secondly, I investigate the halo-scale clustering of unobscured and obscured quasars in order to explore the environments in which these luminous, AGN-dominated sources form. With the difficulty of identifying and detecting the dust-shrouded obscured quasars, the large-scale environment of the population has been relatively understudied in the past decade, but could hold the key to distinguishing between whether the obscuration is a temporary stage resulting from a recent major merger (the evolutionary model), or a permanent feature of the dust structures of the host galaxy (the orientation model). The latter predicts that the environments in which both types of quasars are found should be similar, and indeed in the range of 1.3 < z < 2.5 for Spitzer IR-selected obscured and unobscured quasars, I calculate similar median clustering amplitudes, indicating nearly identical large-scale environments. These results are discussed in the context of numerous other findings in the field.
PHD (Doctor of Philosophy)
Quasars, AGN, SMBH, supermassive black holes