An HST/WFC3-IR Morphological Survey of Galaxies at z = 1.5-3.6: I. Survey Description and Morphological Properties of Star Forming Galaxies

TL;DR

This study uses HST/WFC3 imaging to analyze the rest-frame optical morphologies of star forming galaxies at redshifts 1.5 to 3.6, revealing their sizes, shapes, and structural properties, and exploring their relation to galaxy mergers and evolution.

Contribution

First detailed morphological survey of star forming galaxies at z=1.5-3.6 using HST/WFC3, providing insights into their sizes, shapes, and merger characteristics.

Findings

Galaxies have effective radii of 0.7-3.0 kpc, following a stellar mass-radius relation at z~3.

Galaxy shapes are better described by triaxial systems than inclined disks.

Meromorphic features do not strongly correlate with physical properties like stellar mass or star formation rate.

Abstract

We present the results of a 42-orbit HST/WFC3 survey of the rest-frame optical morphologies of star forming galaxies with spectroscopic redshifts in the range z=1.5-3.6. The survey consists of 42 orbits of F160W imaging covering ~65 arcmin^2 distributed widely across the sky and reaching a depth of 27.9 AB for a 5 sigma detection within a 0.2 arcsec radius aperture. Focusing on an optically selected sample of 306 star forming galaxies with stellar masses in the range M* = 10^9 - 10^11 Msun, we find that typical circularized effective half-light radii range from ~ 0.7 - 3.0 kpc and describe a stellar mass - radius relation as early as z ~ 3. While these galaxies are best described by an exponential surface brightness profile, their distribution of axis ratios is strongly inconsistent with a population of inclined exponential disks and is better reproduced by triaxial stellar systems with minor/major and intermediate/major axis ratios ~ 0.3 and 0.7 respectively. While rest-UV and rest-optical morphologies are generally similar for a subset of galaxies with HST/ACS imaging data, differences are more pronounced at higher masses M* > 3 x 10^10 Msun. Finally, we discuss galaxy morphology in the context of efforts to constrain the merger fraction, finding that morphologically-identified mergers/non-mergers generally have insignificant differences in terms of physical observables such as stellar mass and star formation rate, although merger-like galaxies selected according to some criteria have statistically smaller effective radii and correspondingly larger SFR surface density.