UC Irvine

In this dissertation, we present three studies of various extragalactic sources at infrared wavelengths. In Chapter 1, we used stacking to find the average far-infrared spectra of a sample of 197 dusty, star-forming galaxies (DSFGs) at 0.005 < z < 4 using about 90% of the Herschel Space Observatory SPIRE Fourier Transform Spectrometer (FTS) extragalactic data archive based on 3.5 years of science operations. These spectra explore an observed-frame 447 GHz - 1568 GHz frequency range allowing us to observe the main atomic and molecular lines emitted by gas in the interstellar medium. These stacked spectra are used to determine the average gas density and radiation field strength in the photodissociation regions (PDRs) of dusty, star-forming galaxies. For the high-z (0.8 < z < 4) sample, PDR models suggest a molecular gas distribution in the presence of a radiation field that is at least a factor of 10^3 larger than the Milky-Way and with a neutral gas density of roughly 10^4.5 to 10^5.5 cm^-3. The corresponding PDR models for the low-z sample suggest a UV radiation field and gas density comparable to those at high-z. In Chapter 2, we use multi-band optical and near-infrared photometric observations of galaxies in the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) to predict photometric redshifts using an artificial neural network called a Self-Organizing Map (SOM). The multi-band observations span over 0.39 µm to 8.0 µm for a sample of ∼1000 galaxies in the GOODS-S field for which robust size measurements are available from Hubble Space Telescope Wide Field Camera 3 observations. We use the SOM to map the multi-dimensional photometric and galaxy size observations while taking advantage of existing spectroscopic redshifts at 0 < z < 2 for independent training and testing sets. We show that use of photometric and morphological data led to redshift estimates comparable to redshift measurements from SED modeling and from self-organizing maps without morphological measurements. In Chapter 3, power spectrum methods are used to study fluctuations in the cosmic infrared background with hopes of finding a signature of intra-halo light. We use images of the North Ecliptic Pole (NEP) region observed by Spitzer and the Herschel Space Observatory to compute the cross-power spectra between Spitzer 3.6 µm and 4.5 µm sky maps and Herschel 250 µm, 350 µm, and 500 µm sky maps. Weak correlations are found between each of the Spitzer \times Herschel wavelengths (e.g., 3.6 µm x 250 µm), suggesting that there might be some weak correlated emission between near- and far-infrared wavelengths.