Young Galaxy Candidates in the Hubble Frontier Fields - III. MACSJ0717.5+3745

TL;DR

This study identifies and analyzes high-redshift galaxy candidates behind the MACSJ0717.5+3745 cluster using Hubble and Spitzer data, revealing insights into galaxy evolution and the decline in star formation rate density at z > 8.

Contribution

First comprehensive analysis of z > 6 galaxy candidates behind MACSJ0717.5+3745 combining Hubble and Spitzer data, improving understanding of early galaxy properties and evolution.

Findings

39 high-z galaxy candidates identified

Evidence for evolution of galaxy number density between z~8 and 9

Strong decrease in star formation rate density from z~8 to 9

Abstract

In this paper we present the results of our search for and study of $z \gtrsim 6$ galaxy candidates behind the third Frontier Fields (FF) cluster, MACSJ0717.5+3745, and its parallel field, combining data from Hubble and Spitzer. We select 39 candidates using the Lyman Break technique, for which the clear non-detection in optical make the extreme mid-$z$ interlopers hypothesis unlikely. We also take benefit from $z \gtrsim 6$ samples selected using previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the constraints on the properties of very high-redshift objects. We compute the redshift and the physical properties, such emission lines properties, star formation rate, reddening, and stellar mass for all Frontier Fields objects from their spectral energy distribution using templates including nebular emission lines. We study the relationship between several physical properties and confirm the trend already observed in previous surveys for evolution of star formation rate with galaxy mass, and between the size and the UV luminosity of our candidates. The analysis of the evolution of the UV Luminosity Function with redshift seems more compatible with an evolution of density. Moreover, no robust $z\ge$8.5 object is selected behind the cluster field, and few $z$$\sim$9 candidates have been selected in the two previous datasets from this legacy survey, suggesting a strong evolution in the number density of galaxies between $z$$\sim$8 and 9. Thanks to the use of the lensing cluster, we study the evolution of the star formation rate density produced by galaxies with L$>$0.03L$^{\star}$, and confirm the strong decrease observed between $z$$\sim$8 and 9.