UC Davis

Stellar feedback, or the process by which stars inject energy, metals and gas into the interstellar medium (ISM), plays an integral role in the formation and evolution of galaxies. Stellar feedback enriches the ISM with heavy metals formed via star formation, redistributes gas and dust within galaxies, and regulates star formation. In this dissertation I explore the role of stellar feedback in galaxy evolution, namely its ability to alter the dark matter distribution in dwarf galaxies as well as explore systematic effects in measuring galaxy chemical evolution, which is one of the most powerful probes of feedback.

I present the OSIRIS Lens-Amplified Survey (OLAS), a kinematic survey of gravitationally lensed galaxies at z~1-3 taken with Keck adaptive optics, which is designed to address the so-called "cusp-core problem". Simulations suggest that gaseous outflows driven by stellar feedback can be strong enough to alter the total mass distribution of dwarf galaxies. OLAS probes the stellar mass and specific star formation rate (sSFR) range where simulations predict that stellar feedback is most effective at driving gaseous outflows that create galaxy-wide potential fluctuations which can generate dark matter cores. I find a correlation between sSFR and gas phase velocity dispersion at fixed stellar mass that is consistent with the trend predicted by simulations: feedback from star formation drives star-forming gas and newly formed stars into more dispersion dominated orbits. My results support the scenario that stellar feedback drives gaseous outflows and potential fluctuations, which in turn drive dark matter core formation in dwarf galaxies.

I also present spatially resolved Hubble Space Telescope grism spectroscopy of 15 galaxies at z~0.8. I analyze H-alpha+[NII], [SII] and [SIII] emission on kiloparsec scales to explore which mechanisms are powering emission lines at high redshifts. A key goal is to test which processes may be responsible for the well-known offset of high redshift galaxies from the z~0 locus in the [OIII]/H-beta versus [NII]/H-alpha BPT (Baldwin-Phillips-Terlevich) excitation diagram. Offsets in the BPT diagram highlight differing strong emission line ratios (and thus, ISM conditions) at different redshifts, however most studies use strong line ratios measured from local galaxies as a main diagnostic to measure galaxy metallicity. This assumption propagates systematic errors in metallicity measurements to high redshift, and yields more uncertainty in the effects of feedback (i.e., the amount of mass and metal loss) at high redshifts. I study the spatially resolved emission line maps of [SII]/(H-alpha + [NII]) and [SIII]/[SII] as a function of surface brightness and position within a galaxy to examine evidence for active galactic nuclei (AGN), shocks, diffuse ionized gas (DIG), or escaping ionizing radiation, all of which may contribute to the BPT offsets observed in our sample and therefore cause systematic errors in metallicity measurements. In general I find that the observed emission is dominated by star forming HII regions, indicating that the BPT line ratio offsets are caused by different properties of HII regions at high redshift compared to their local counterparts. I discuss trends with demographic properties and the possible role of alpha-enhanced abundance patterns in the emission spectra of high redshift galaxies. These results indicate that photo-ionization modeling with stellar population synthesis inputs is a valid tool to explore the specific star formation properties which may cause BPT offsets, to be explored in future work.

Finally, I discuss how future observations and the next generation of telescope facilities will be able to build upon the results of this dissertation to further understand the role of stellar feedback in galaxy formation through cosmic time.