Lyman Continuum Escape Fraction from Low-mass Starbursts at z=1.3

TL;DR

This study uses deep UV imaging to constrain the escape fraction of ionizing photons from low-mass starburst galaxies at z=1.3, finding no detectable LyC emission and setting upper limits on escape fractions.

Contribution

First constraints on the Lyman Continuum escape fraction from low-mass starburst galaxies at z=1.3 using deep HST UV imaging, with no detections and implications for reionization sources.

Findings

No LyC signal detected in individual or stacked galaxies.

3σ upper limit on relative escape fraction is <0.07 for the stack.

Galaxies have similar properties to confirmed LyC emitters, but do not show detectable LyC escape.

Abstract

We present a new constraint on the Lyman Continuum (LyC) escape fraction at z~1.3. We obtain deep, high sensitivity far-UV imaging with the Advanced Camera for Surveys (ACS) Solar Blind Channel (SBC) on the Hubble Space Telescope (HST), targeting 11 star-forming galaxies at 1.2<z<1.4. The galaxies are selected from the 3D-HST survey to have high H$\alpha$ equivalent width (EW) with EW > 190 \AA, low stellar mass (M* < 10^10 M_sun) and U-band magnitude of U<24.2. These criteria identify young, low metallicity star bursting populations similar to the primordial star-forming galaxies believed to have reionized the universe. We do not detect any LyC signal (with S/N >3) in the individual galaxies or in the stack in the far-UV images. We place $3\sigma$ limits on the relative escape fraction of individual galaxies to be f_{esc,rel}<[0.10-0.22] and a stacked $3\sigma$ limit of f_{esc,rel}<0.07. Comparing to the confirmed LyC emitters from the literature, the galaxies in our sample span similar ranges of various galaxy properties including stellar mass, dust attenuation, and star formation rate (SFR). In particular, we compare the distribution of H$\alpha$ and [OIII] EWs of confirmed LyC emitters and non-detections including the galaxies in this study. Finally, we discuss if a dichotomy seen in the distribution of H$\alpha$ EWs can perhaps distinguish the LyC emitters from the non-detections.