Quantifying the UV continuum slopes of galaxies to z~10 using deep Hubble and Spitzer/IRAC observations

TL;DR

This study measures the UV continuum slopes of galaxies at z~10 using deep Hubble and Spitzer/IRAC data, providing insights into their physical properties and evolution in the early universe.

Contribution

It presents the first mean UV slope measurements for a multi-object sample of galaxies at z~10, leveraging the unique observational window provided by Spitzer/IRAC.

Findings

Measured UV slopes are approximately -2.1 at z~10.

Slopes are only slightly bluer than those at lower redshifts (z=3.5-7.5).

Small increases in age, metallicity, and dust could explain slope evolution.

Abstract

Measurements of the UV-continuum slopes provide valuable information on the physical properties of galaxies forming in the early universe, probing the dust reddening, age, metal content, and even the escape fraction. While constraints on these slopes generally become more challenging at higher redshifts as the UV continuum shifts out of the Hubble Space Telescope bands (particularly at z>7), such a characterisation actually becomes abruptly easier for galaxies in the redshift window z=9.5-10.5 due to the Spitzer/IRAC 3.6um-band probing the rest-UV continuum and the long wavelength baseline between this Spitzer band and the Hubble H-band. Higher S/N constraints on the UV slope are possible at z~10 than at z=8. Here we take advantage of this opportunity and five recently discovered bright z=9.5-10.5 galaxies to present the first measurements of the mean slope for a multi-object sample of galaxy candidates at z~10. We find the measured observed slopes of these candidates are $-2.1\pm0.3\pm0.2$ (random and systematic), only slightly bluer than the measured slopes at 3.5<z<7.5 for galaxies of similar luminosities. Small increases in the stellar ages, metallicities, and dust content of the galaxy population from z~10 to z~7 could easily explain the apparent evolution in slopes.