Poster Presentation
Environmental impacts on the rest-frame UV size and morphology of star-forming galaxies at z ∼ 2
Presenter: Abdurrahman Naufal (SOKENDAI/NAOJ)
In the local Universe, we observe that environment has an important role in affecting the structure and morphology of galaxies, as well as their physical properties. In the densest environments such as galaxy clusters, galaxies are predominantly quiescent ellipticals, while in less dense environments star-forming disk galaxies are more prevalent. How and when environment starts to play such role is an important question in galaxy evolution.
Protoclusters—overdense regions at high redshift thought to be the progenitors of today’s galaxy clusters—are unique laboratories to investigate how environment affects the properties of galaxies in the earlier stages of their evolution. With the increasing number of protoclusters surveyed, we aim to characterize the structure and morphology of galaxies in protoclusters to investigate their environmental dependence.
We compile catalogs of four protoclusters at z ∼ 2 (PKS 1138-262, USS 1558-003, PHz G237.0+42.5, and CC 2.2) consisting of 331 Hα-emitting star-forming galaxies (HAE) and characterize their size and apparent morphologies observed by the Hubble Space Telescope Advanced Camera Surveys (HST/ACS) in the F814W filter. We compare the structures of 138 HAEs in protoclusters detected by HST/ACS to a coeval comparison field sample of 462 HAEs. We measure the size by Sérsic profile fitting as well as the morphologies by non-parametric methods.
We find the size distributions of protocluster and field HAEs at are similar with typical half-light radius of ∼ 2.5 kpc. At fixed stellar mass, there is no significant difference between HAE in protocluster and in field. Stacking analyses also show similar results. This result suggests that the environment does not significantly affect the size of galaxies during the star-forming phase.
Based on Sérsic index and non-parametric morphologies, HAE morphologies at z~2 in rest-frame UV are consistent with disk-like star-forming galaxies, although we also find ∼20% HAEs have peculiar morphologies. We find that rotocluster HAEs are slightly more concentrated than field HAEs, especially in the highly star-forming subsamples. If we interpret peculiar morphologies as merger candidates according on Gini-M20 merger statistics, we estimate the merger fraction in protoclusters is 38 ± 7% protocluster and 26 ± 3% field. We also find that there is twice more peculiar galaxies above star-forming main sequence than below it, suggesting the correlation between starbursts and peculiar morphologies, which may be caused by the presence giant star-forming clumps or merger signatures.
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