On the faint-end of the galaxy luminosity function in the Epoch of Reionization: updated constraints from the HST Frontier Fields.
2017
Ultra-
faintgalaxies are hosted by small
dark matter haloswith shallow
gravitational potentialwells, hence their
star formationactivity 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 formationand its interaction with the
reionizationprocess 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 {\it 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
faintmagnitudes. 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-14.6 $ (15.2) at 1 (2) $\sigma$ confidence level (C.L.) for $z\sim6$. In the physically-motivated analytical model,
star formationin 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 $v_c^*\lesssim 59$ km s$^{-1}$ and $f_{\rm esc}\lesssim 56\%$ (both at 2$\sigma$ C.L.) and conclude that there is no turn-over detected so far from the analyzed FFs data. Forthcoming {\it JWST} observations will be key to tight these constraints further.
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