On the faint-end of the galaxy luminosity function in the Epoch of Reionization: updated constraints from the HST Frontier Fields

B. Yue, M. Castellano, A. Ferrara, A. Fontana, E. Merlin, R. Amorín, A. Grazian, E. Mármol-Queralto, M. J. Michałowski, A. Mortlock, D. Paris, S. Parsa, S. Pilo, P. Santini, M. Di Criscienzo

Published 2017-11-14Version 1

Ultra-faint galaxies are hosted by small dark matter halos with shallow gravitational potential wells, hence their star formation activity is more sensitive to feedback effects. The shape of the faint-end of the high-$z$ galaxy luminosity function (LF) contains important information on star formation and its interaction with the reionization process during the Epoch of Reionization (EoR). High-$z$ galaxies with $M_{\rm UV}\gtrsim-17$ have only recently become accessible thanks to the Frontier Fields (FFs) survey combining deep HST imaging and the gravitational lensing effect. In this paper we investigate the faint-end of the LF at redshift $>$5 using the data of FFs clusters Abell 2744 (A2744), MACSJ0416.1-2403 (M0416), MACSJ0717.5+3745 (M0717) and MACSJ1149.5+2223 (M1149). We analyze both an empirical and a physically-motivated LF model to obtain constraints on a possible turn-over of LF at faint magnitudes. In the empirical model the LF drops fast when the absolute UV magnitude $M_{\rm UV}$ is much larger than a turn-over absolute UV magnitude $M_{\rm UV}^{\rm T}$. We obtain $M_{\rm UV}^{\rm T}\gtrsim-14.3$ at 2$\sigma$ confidence level (C.L.) for $z\sim6$. In the physically-motivated analytical model, star formation in halos with circular velocity below $v_c^*$ is fully quenched if these halos are located in ionized regions. Using updated lensing models and new additional FFs data, we re-analyze previous constraints on $v_c^*$ and $f_{\rm esc}$ presented by Castellano et al. 2016a (C16a) using a smaller dataset. We obtain new constraints on $v_c^*\lesssim 57$ km s$^{-1}$ and $f_{\rm esc}\lesssim 63\%$ (both at 2$\sigma$ C.L.) and conclude that there is no turn-over detected so far from the analyzed FFs data. Forthcoming JWST observations will be key to tight these constraints further.