An HST/WFC3-IR Morphological Survey of Galaxies at z = 1.5-3.6: II. The Relation between Morphology and Gas-Phase Kinematics

TL;DR

This study investigates how galaxy morphology at redshifts 2-3 correlates with gas-phase kinematics and LyA emission, revealing that compact galaxies are more likely to show LyA in emission and have distinct outflow properties.

Contribution

It provides new insights into the relationship between galaxy morphology, gas outflows, and LyA emission at high redshift, highlighting differences from lower-redshift galaxies.

Findings

Compact galaxies more likely to exhibit LyA emission.

Larger galaxies have less ionized outflows and more systemic gas.

No correlation between outflow velocity and galaxy inclination.

Abstract

We analyze rest-frame optical morphologies and gas-phase kinematics as traced by rest-frame far-UV and optical spectra for a sample of 204 star forming galaxies in the redshift range z ~ 2-3 drawn from the Keck Baryonic Structure Survey (KBSS). We find that spectroscopic properties and gas-phase kinematics are closely linked to morphology: compact galaxies with semi-major axis radii r <~ 2 kpc are substantially more likely than their larger counterparts to exhibit LyA in emission. Although LyA emission strength varies widely within galaxies of a given morphological type, all but one of 19 galaxies with LyA equivalent width W_LyA > 20 Angstroms have compact and/or multiple-component morphologies with r <= 2.5 kpc. The velocity structure of absorption lines in the galactic continuum spectra also varies as a function of morphology. Galaxies of all morphological types drive similarly strong outflows (as traced by the blue wing of interstellar absorption line features), but the outflows of larger galaxies are less highly ionized and exhibit larger optical depth at the systemic redshift that may correspond to a decreasing efficiency of feedback in evacuating gas from the galaxy. This v ~ 0 km/s gas is responsible both for shifting the mean absorption line redshift and attenuating W_LyA (via a longer resonant scattering path) in galaxies with larger rest-optical half light radii. In contrast to galaxies at lower redshifts, there is no evidence for a correlation between outflow velocity and inclination, suggesting that outflows from these puffy and irregular systems may be poorly collimated. (Abbrev.)