COSMOS2020: UV-selected galaxies at z  ≥  7.5

Abstract

This paper presents a new search for z ≥ 7.5 galaxies using the COSMOS2020 photometric catalogues. Finding galaxies at the reionisation epoch through deep imaging surveys remains observationally challenging. The larger area covered by ground-based surveys such as COSMOS enables the discovery of the brightest galaxies at these high redshifts. Covering 1.4 deg 2 , our COSMOS catalogues were constructed from the latest UltraVISTA data release (DR4) combined with the final Spitzer/IRAC COSMOS images and the Hyper-Suprime-Cam Subaru Strategic Program DR2 release. We identified 17 new 7.5 < z < 10 candidate sources, and confirm 15 previously published candidates. Using deblended photometry extracted by fitting surface brightness models on multiband images, we selected four candidates which would be rejected using fixed aperture photometry. We tested the robustness of all our candidates by comparing six different photometric redshift estimates. Finally, we computed the galaxy UV luminosity function in three redshift bins centred at z = 8, 9, 10. We find no clear evolution of the number density of the brightest galaxies M UV < −21.5, in agreement with previous works. Rapid changes in the quenching efficiency or attenuation by dust could explain such a lack of evolution between z ∼ 8 and z ∼ 9. A spectroscopic confirmation of the redshifts, already planned with JWST and the Keck telescopes, will be essential to confirm our results.

COSMOS-Web: An Overview of the JWST Cosmic Origins Survey

“…Such snapshots of the density field will provide a direct test as to whether or not the brightest, most-massive galaxies are indeed highly clustered, as suggested by cosmological simulations (e.g., McQuinn et al 2007;Behroozi et al 2013;Chiang et al 2017). Though some massive galaxies have been identified at this epoch from Ultra-VISTA data (Bowler et al 2020;Endsley et al 2023;Kauffmann et al 2022), it remains to be seen whether or not they sit in overdense environments. Existing Hubble and other planned JWST surveys are insufficient to answer this question due to their limited areas; however, COSMOS-Web will have both the depth and area to enable this measurement.…”

“…Khostovan et al 2023, in preparation), including from large surveys such as zCOSMOS (Lilly et al 2007(Lilly et al , 2009, FMOS-COSMOS (Kartaltepe et al 2015b;Silverman et al 2015;Kashino et al 2019), VUDS (Le Fèvre et al 2015, and many programs using Keck (e.g., Kartaltepe et al 2010;Capak et al 2011;Casey et al 2012;Kriek et al 2015;Hasinger et al 2018), greatly enhancing the accuracy of photometric redshifts for all sources in the field. Lastly, the quality of photometric redshifts Δz/(1 + z) < 0.02 for galaxies with i < 25 (Ilbert et al 2013;Laigle et al 2016;Weaver et al 2022b) has facilitated the discovery and analysis of galaxies out to z ∼ 7 and beyond (Bowler et al 2017(Bowler et al , 2020Stefanon et al 2019;Kauffmann et al 2022). The photometric redshifts will be further improved with the addition of COSMOS-Web (see Section 2.5), dramatically improving the accuracy of the weak lensing measurement of galaxies' halo mass as well as galaxies' stellar masses and SFRs across all epochs.…”

Life beyond 30: Probing the −20 < M UV < −17 Luminosity Function at 8 < z < 13 with the NIRCam Parallel Field of the MIRI Deep Survey

“…For that purpose, we allowed the color excess E(B − V ) to range from 0 to 1.5 mag (with steps of 0.1), reaching A V ; 6 mag. A second configuration was explored, this time following the one described in Ilbert et al (2015), Kauffmann et al (2022). Since our aim is to select rare sources at z > 8, we explore a large range of dust-attenuation in order to identify and reject possible contaminants.…”

Target Selection and Sample Characterization for the DESI LOW-Z Secondary Target Program

“…Part of the difficulty in obtaining comprehensive samples of faint, low-redshift objects is due to the fact that although these objects are nearby on cosmic scales, separating them from the dominant background of high-redshift objects remains challenging. Significant effort has gone into accurate photometric redshifts (photo-zʼs) for galaxy evolution and cosmology (Baum 1962;Benítez 2000;Collister & Lahav 2004;Feldmann et al 2006;Ilbert et al 2006;Brammer et al 2008;Lee & Chary 2020;Li et al 2023), and also into designing photometric cuts to efficiently select high-redshift objects (e.g., Steidel et al 1996;Daddi et al 2004;Bouwens et al 2015;Finkelstein et al 2015;Ono et al 2018;Bowler et al 2020;Kauffmann et al 2022). However, analogous algorithms for selecting low-redshift objects have historically received less attention.…”