Testing both Modes of Galaxy Formation: A Closer Look at Galaxy Mergers and Gas Accretion
AdvisorZabludoff, Ann I
Committee ChairZabludoff, Ann I
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PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThis thesis focuses primarily on how two important processes --- galaxymergers and gas accretion from the surrounding intergalactic medium ---affect the evolution of galaxies.Using post-starburst, or E+A, galaxies as a marker sample that undergoesa rapid transition from gas-rich star-forming galaxies to quiescent,passively-evolving E/S0s, we study what triggers E+A evolution andwhat E+A galaxies will become after the fading of their young stellarpopulation. With high resolution HST WFPC2/ACS imaging, we investigatetheir small and large scale properties, including their detailedmorphologies, bulge fractions, color gradients, scaling relationships,and newly formed star-clusters. 70% of E+A galaxies show disturbancesand tidal features indicating a merger origin and all their propertiesare either consistent with those of E/S0s or, if left to evolve passively,will become like those of early-types.Using cosmological simulations, we study hydrogen and helium gravitationalcooling radiation from gas accretion by young galaxies, finding thatobserving optically thin cooling lines such as HeII 1640 and hydrogenHalpha is critical in understanding the nature of galaxies forming viagas-accretion. To obtain an unbiased sample of Lyman alpha blobs thatwill allow us to follow-up their optically thin Halpha lines in the NIR,we conduct a blind, wide-field, narrow-band imaging survey for Lymanalpha blobs. After searching over 4.82 deg^2, we discover four blobsthat we spectroscopically confirm to lie at z=2.3. The properties ofthese blobs are diverse: two blobs are X-ray-detected and have broadoptical emission lines (e.g., CIV) characteristic of AGN. The other50\% of blobs are not X-ray or optically-detected as AGN down tosimilar limits. The number density of the four blobs is extremely low,~3 x 10^-6 Mpc^-3, comparable to that of galaxy clusters at similarredshifts. The two X-ray undetected blobs are separated by only 70"(550 kpc) and have almost identical redshifts (corresponding to < 360kpc along the line-of-sight), suggesting that they are part of the samesystem. Given the rarity of the blobs and our discovery of a close pair,we speculate that blobs occupy the highest density regions and thus maybe precursors of today's rich cluster galaxies.