Young Galaxy Candidates in the Hubble Frontier Fields. Iii. MACS J0717.5+3745

Abstract

In this paper we present the results of our search for and study of z 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 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 ≥8.5 object is selected behind the cluster field, and few z∼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∼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 , and confirm the strong decrease observed between z∼8 and 9.

The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties

“…Small differences in the assumed half-light radii have the potential to change the inferred faintend slopes by large factors, i.e., 0.3  a D depending on whether the mean size of extremely faint galaxies is 120 mas, 30 mas, or 7.5 mas (e.g., see Figure 2 from Bouwens et al 2017). Fortunately, we found that most of the extremely faint sources seem consistent with being almost unresolved, i.e., with intrinsic sizes of <10-30 mas (Bouwens et al 2017; see also Kawamata et al 2015;Laporte et al 2016), making this issue much more manageable in terms of its impact; but it still remains an uncertainty. A second source of systematic error arises from errors in the magnification maps, since this can have a profound impact on the LFs derived.…”

“…Based on recent results from a number of papers (Bouwens et al 2017; see also Laporte et al 2016), it is now clear that the use of such large sizes for very faint galaxies is not realistic. Several lines of evidence indicate that the intrinsic half-light radii of very low luminosity sources (i.e., 16 mag >-) are very small, i.e., 0 03, with many sources appearing to have sizes 0 01 (Bouwens et al 2017).…”

“…At z∼2-3, it has been similarly possible (Alavi et al 2014(Alavi et al , 2016 to probe to approximately−13 mag taking advantage of very deep WFC3/ UVIS observations over Abell 1689 and various clusters in the HFF program. Based on these deep searches, the volume density of galaxies at 16 mag >-have been estimated, with quoted faintend slopes for z∼2-3 LFs that range from −1.6 to −1.9 (Alavi et al 2014(Alavi et al , 2016 and from −1.9 to −2.1 for z∼6-8 LFs (Atek et al 2015a(Atek et al , 2015bIshigaki et al 2015;Castellano et al 2016b;Laporte et al 2016; L17), respectively.…”

Lens models under the microscope: comparison ofHubble Frontier Fieldcluster magnification maps

“…The HFF project has been remarkably prolific, with contributions in the structure of galaxy clusters (Jauzac et al 2014;Richard et al 2014;Ogrean et al 2015;Jauzac et al 2015), individual high redshift galaxies (McLeod et al 2015;Kawamata et al 2015;Laporte et al 2016), and high redshift galaxy luminosity function and its evolution (Finkelstein et al 2015;Coe et al 2015;Atek et al 2015) 1 .…”

The photometric properties of galaxies in the early Universe

“…As of 2016 there are now ∼1000 candidate objects, encompassing a wide range of luminosities, identified (e.g. Bouwens et al 2010Bouwens et al , 2011Bouwens et al , 2014aBouwens et al ,b, 2015aOesch et al 2010Oesch et al , 2013Oesch et al , 2014Oesch et al , 2015Oesch et al , 2016Bunker et al 2010;Wilkins et al 2010Wilkins et al , 2011aFinkelstein et al 2010Finkelstein et al , 2012Finkelstein et al , 2015Lorenzoni et al 2011Lorenzoni et al , 2013McLure et al 2011McLure et al , 2013Ellis et al 2013;Laporte et al 2014Laporte et al , 2015Laporte et al , 2016Schmidt et al 2014;McLeod et al 2015;McLeod, McLure & Dunlop 2016;Atek et al 2015a, Atek et al2015b) with the first small samples now identified at z ∼ 10 and beyond.…”