Quantifying the Physical Properties of High-Redshift Galaxies: A Multi-wavelength Survey on the Progenitors of Local Galaxies
Since the discovery of galaxies outside of the Milky Way, studies of nearby galaxies have revealed a very different population of galaxies compared to distant galaxies. My thesis has been motivated by galaxy evolution. In particular, I focus on the connection between nearby and distant galaxies, changes in morphologies with wavelength, and the physical properties of galaxies when the Universe was 1.5 (z = 4) to 6 (z = 1) Gyr old. Rest-frame far-ultraviolet morphologies of 8 nearby interacting and starburst galaxies are artificially redshifted and compared with 54 galaxies at z ∼ 1.5 and 46 galaxies at z ∼ 4. I calculated the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M20), and the Sérsic index (n). I showed that ∼20-30% of Lyman-break galaxies have structures similar to local starburst mergers, and may be driven by similar processes. I also determined that Mrk 8, NGC 3079, and NGC 7673 have structures similar to merger-like and clumpy star-forming galaxies observed at z ∼ 1.5 and 4. I selected 301 galaxies from the Ultra Deep Field parallel survey (UDF05) done with HST's infrared camera, NICMOS, to calculate their spectral energy distributions (SEDs). The galaxies are cross-matched using HST ACS and NICMOS filters, and the infrared Spitzer IRAC filters. Photometric redshifts, dust extinction, stellar masses, bolometric luminosity, starburst age and metallicity are estimated through Balmer-break SED fitting. Comparisons of 16 photometric redshifts with spectroscopic redshifts give 75% agreement. I determined through Monte Carlo simulations that the SED parameters are robust for the redshift ranges z > 1.2. I find that luminosities and star formation rates increase with redshift for a subsample of galaxies at z ∼ 1.5 and z ∼ 4. I demonstrate that multi-wavelength analysis is fundamental to the understanding of galaxy evolution. I determined that G-M20 values of Balmer-break galaxies are more bulge-like in the rest-frame optical than z ∼ 1 and 4 starburst galaxies in the UV. I conclude that the Balmer-break selected galaxies are probably progenitors to local early type galaxies.
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