CANUCS: UV and Ionising Properties of Dwarf Star Forming Galaxies at z = 5 to 7

Abstract

The epoch of reionisation progressed through the emission of ionising photons from galaxies to their local intergalactic medium. In this work, we characterise the dwarf star-forming galaxies as candidates for the source of ionising photons that drove EoR. We investigate the ionising properties and star formation histories of star-forming dwarf galaxies at the last stages of EoR at $4.8<\mathrm{z}<7$ using observations from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The magnification due to gravitational lensing allows us to probe large dynamic ranges in stellar mass ($2\times 10^6\le {\mathrm{M}}_{\ast }/{\mathrm{M}}_{\odot }\le 5\times 10^9$) and UV magnitudes ($-22.68\le$M${}_{UV}\le =-15.95$).We find a median UV slope \buv of $-2.56\pm 0.23$ and the production efficiency of ionising photons $\log$ \xiion $=25.39\pm 0.6$ for the full sample ($4.8<\mathrm{z}<7$) with a median stellar mass of $6.3\pm 0.5\times 10^7{\mathrm{M}}_{\odot }$. We find both \buv and \xiion are marginally correlated with the stellar mass of the galaxy, indicating a possible greater contribution of dwarf galaxies to the reionisation of the Universe. We find that on average, galaxies in our sample are experiencing a recent rise/burst of star formation which translates to a higher scatter in \xiion and a large scatter in H$\hat{I}\pm$ equivalent widths. Finally, we investigate the trends of H$\hat{I}\pm$ and [OIII]+H${\hat{I}}^2$ EWs with UV magnitude and find M${}_{UV}$ is correlated between H$\hat{I}\pm$ but not with [OIII]+H${\hat{I}}^2$ EWs indicating low metallicities and recent burst in the UV faint galaxies.

Accepted For Publication in MNRAS