Testing both modes of galaxy formation: A closer look at galaxy mergers and gas accretion
Abstract
This thesis focuses primarily on how two important processes--galaxy mergers 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 undergoes a rapid transition from gas-rich star-forming galaxies to quiescent, passively-evolving E/S0s, we study what triggers E+A evolution and what E+A galaxies will become after the fading of their young stellar population. With high resolution HST WFPC2/ACS imaging, we investigate their small and large scale properties, including their detailed morphologies, bulge fractions, color gradients, scaling relationships, and newly formed star- clusters. 70% of E+A galaxies show disturbances and tidal features indicating a merger origin and all their properties are 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 gravitational cooling radiation from gas accretion by young galaxies, finding that observing optically thin cooling lines such as He II l1640 and H I Ha is critical in understanding the nature of galaxies forming via gas-accretion. To obtain an unbiased sample of Lya blobs that will allow us to follow-up their optically thin Ha lines in the NIR , we conduct a blind, wide-field, narrow-band imaging survey for Lya blobs. After searching over 4.82 deg 2 , we discover four blobs that we spectroscopically confirm to lie at z = 2.3. The properties of these blobs are diverse: two blobs are X-ray-detected and have broad optical emission lines (e.g., C IV) characteristic of AGN. The other 50% of blobs are not X-ray or optically-detected as AGN down to similar limits. The number density of the four blobs is extremely low, ~3 × 10^-6 [Special characters omitted.] Mpc -3 , comparable to that of galaxy clusters at similar redshifts. The two X-ray undetected blobs are separated by only 70" (550 kpc) and have almost identical redshifts (corresponding to [Special characters omitted.] 360 kpc along the line-of-sight), suggesting that they are part of the same system. Given the rarity of the blobs and our discovery of a close pair, we speculate that blobs occupy the highest density regions and thus may be precursors of today's rich cluster galaxies.- Publication:
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Ph.D. Thesis
- Pub Date:
- 2008
- Bibcode:
- 2008PhDT.........1Y
- Keywords:
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- Galaxy formation;
- Galaxy mergers;
- Gas accretion;
- Cooling radiation