Morphologies of Galaxies in and around a Protocluster atz= 2.300

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Abstract
We present results from the first robust investigation of galaxy morphology as a function of environment at z>1.5. Our study is motivated by the fact that star-forming galaxies contained within a protocluster at z=2.3 in the HS1700+64 field have significantly older ages and larger stellar masses on average than those at similar redshifts but more typical environmental densities. In the analysis of HST/ACS images, we apply non-parametric statistics to characterize the rest-frame UV morphologies of a sample of 85 UV-selected star-forming galaxies at z=1.7-2.9, 22 of which are contained in the protocluster. The remaining 63 control-sample galaxies are not in the protocluster but have a similar mean redshift of ~2.3. We find no environmental dependence for the distributions of morphological properties. Combining the measured morphologies with the results of population synthesis modeling, we find only weak correlations, if any, between morphological and stellar population properties such as stellar mass, age, extinction and star-formation rate. Given the incomplete census of the protocluster galaxy population, and the lack of correlation between rest-frame UV morphology and star-formation history at z~2 within our sample, the absence of environmental trends in the distribution of morphological properties is not surprising. Additionally, using a larger sample of photometric candidates, we compare morphological distributions for 282 UV-selected and 43 near-IR-selected galaxies. While the difference in the degree of nebulosity between the two samples appears to be a byproduct of the fainter average rest-frame UV surface brightness of the near-IR-selected galaxies, we find that, among the lowest surface brightness galaxies, the near-IR-selected objects have significantly smaller angular sizes (abridged).Comment: 25 pages including 16 figures. Accepted for publication in ApJ. Version with full resolution figures available at http://www.astro.princeton.edu/~apeter/LBG/papers/peter2007_fullres.ps.g
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