COSMOS2020: UV selected galaxies at $z\geq7.5$

TL;DR

This study searches for galaxies at redshifts greater than 7.5 using the COSMOS2020 catalog, identifying new candidates and analyzing their luminosity function to understand galaxy evolution during reionization.

Contribution

It introduces a new method combining deblended photometry and multiple redshift estimates to identify high-redshift galaxy candidates in the COSMOS2020 survey.

Findings

Identified 17 new high-redshift galaxy candidates.

Found no significant evolution in the brightest galaxy number density from z=8 to z=10.

Confirmed the robustness of candidates through multiple photometric redshift methods.

Abstract

This paper presents a new search for $z\geq7.5$ galaxies using the COSMOS2020 photometric catalogues. Finding galaxies at the reionization epoch through deep imaging surveys remains observationally challenging. The larger area covered by ground-based surveys like 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 identify $17$ new $7.5<z<10$ candidate sources, and confirm $15$ previously published candidates. Using deblended photometry extracted by fitting surface brightness models on multi-band images, we select four candidates which would be rejected using fixed aperture photometry. We test the robustness of all our candidates by comparing six different photometric redshift estimates. Finally, we compute 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 $M_\text{UV}<-21.5$, in agreement with previous works. Rapid changes in the quenching efficiency or attenuation by dust could explain such lack of evolution between $z\sim 8$ and $z\sim 9. A spectroscopic confirmation of the redshifts, already planned with JWST and the Keck telescopes, will be essential to confirm our results.