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arXiv · 2205.11526

z~2-9 Galaxies Magnified by the Hubble Frontier Field Clusters II: Luminosity Functions and Constraints on a Faint-End Turnover

R. J. Bouwens·G. D. Illingworth·R. S. Ellis·P. A. Oesch·M. Stefanon
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Abstract

We present new determinations of the rest-UV luminosity functions (LFs) at z=2-9 to extremely low luminosities (>-14 mag) from a sample of >2500 lensed galaxies found behind the HFF clusters. For the first time, we present faint-end slope results from lensed samples that are fully consistent with blank-field results over the redshift range z=2-9, while reaching to much lower luminosities than possible from the blank-field studies. Combining the deep lensed sample with the large blank-field samples allows us to set the tight constraints on the faint-end slope alpha of the z=2-9 UV LFs and its evolution. We find a smooth flattening in alpha from -2.28+/-0.10 (z=9) to -1.53+/-0.03 (z=2) with cosmic time (d(alpha)/dz=-0.11+/-0.01), fully consistent with dark matter halo buildup. We utilize these new results to present new measurements of the evolution in the UV luminosity density rho(UV) brightward of -13 mag from z~9 to z~2. Accounting for the SFR densities to faint luminosities implied by our LF results, we find that unobscured star formation dominates the SFR density at z>~4, with obscured star formation dominant thereafter. Having shown we can quantify the faint-end slope alpha of the LF accurately with our lensed HFF samples, we also quantify the apparent curvature in the shape of the UV LF through a curvature parameter delta. The constraints on the curvature delta strongly rule out the presence of a turn-over brightward of -13.1 mag at z~3, -14.3 mag at z~6, and -15.5 mag at all other redshifts between z~9 to z~2.

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R. J. Bouwens, G. D. Illingworth, R. S. Ellis, P. A. Oesch, M. Stefanon. 2022-05-23. z~2-9 Galaxies Magnified by the Hubble Frontier Field Clusters II: Luminosity Functions and Constraints on a Faint-End Turnover. https://doi.org/10.3847/1538-4357%2Fac86d1

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