A Mid-Infrared Study of Blue Compact Dwarf Galaxies
Blue Compact Dwarf Galaxies (BCDs) are characterized by their blue optical colors, low luminosities and small sizes. Typically BCDs are found to have low, subsolar metallicities, and they are proposed to be local analogs to the primeval galaxies in the early universe. The unprecedented sensitivity of the Spitzer Space Telescope has enabled, for the first time, the detection of a large sample of these low luminosity systems. In this dissertation, I will present my work employing Spitzer data to study the dust properties and chemical evolution of blue compact dwarf galaxies. Using Spitzer/IRS low-resolution spectra (R~100), I investigated the presence/absence of the Polycyclic Aromatic Hydrocarbon (PAH) features in low-metallicity galaxies. After exploring different physical parameters, I find that the strength of PAH emission is best correlated with a combination of formation and destruction effects. In addition, using the high-resolution sectroscopy (R~600), I study the elemental abundances of neon and sulfur in BCDs and compare with the optical studies. I find that the infrared derived elemental abundances generally agree with the optical results, though the neon abundances are slightly higher from our study. I also analyze the FIR/radio correlation in BCDs and expand the discussion to the mid-IR. I find that the infrared luminosities are well correlated with the radio luminosities even in these low luminosity systems. A study on the spectral energy distribution (SED) and star formation rates (SFRs) in low-luminosity star-forming galaxies is also included in this thesis. The SEDs appear to be warmer than normal star-forming galaxies, and their SFRs vary over an order of magnitude. Finally, I also present a case study on the famous BCD IZw18, showing the first mid-infrared spectrum for this galaxy.