MOSEL Survey: Extremely weak outflows in EoR analogues at z=3-4

TL;DR

This study investigates the properties of galaxies at redshifts 3-4 with extreme emission lines, revealing weak outflows and suggesting suppressed winds or complex outflow structures in these early universe analogues.

Contribution

It provides the first detailed spectroscopic analysis of EoR analogue galaxies at z=3-4, highlighting their weak outflows and implications for galaxy evolution models.

Findings

Weak broad emission components indicating low-velocity outflows

Mass loading factor estimated at ~0.2, similar to lower-redshift galaxies

Outflow signatures do not significantly vary with stellar mass or emission strength

Abstract

This paper presents deep K-band spectroscopic observations of galaxies at z=3-4 with composite photometric rest-frame Hb+[OIII] equivalent widths EW_0>600A, comparable to the EW of galaxies observed during the epoch of reionisation (EoR, z>6). The typical spectroscopic [OIII] EW_0 and stellar mass of our targets is ~ 700A and log(M_star/M_sun)=8.98. By stacking the [OIII] emission profiles, we find evidence of a weak broad component with F_broad/F_narrow ~ 0.2 and velocity width sigma_{broad} ~ 170 km/s. The strength and velocity width of the broad component does not change significantly with stellar mass and [OIII] EW_0 of the stacked sample. Assuming similar broad component profiles for [OIII] and Halpha emission, we estimate a mass loading factor ~0.2, similar to low stellar mass galaxies at z>1 even if the star formation rates of our sample is 10 times higher. We hypothesize that either the multi-phase nature of supernovae driven outflows or the suppression of winds in the extreme star-forming regime is responsible for the weak signature of outflows in the EoR analogues.