2023ApJ...946...90M

We estimate the UV continuum slope (β) of 465 galaxies (with luminosities of 0.028-3.3 ${L}_{z=0.5}^{* }$) in the Great Observatories Origins Survey Northern field in the redshift range z = 0.40-0.75. We use two AstroSat/UVIT (N242W, N245M) bands, two Hubble Space Telescope (F275W, F336W) bands, and a KPNO (U) band to sample the UV continuum slope of selected galaxies between 1215 and 2600 Å. The mean (median) and 1σ scatter in the observed β are found to be -1.33 ± 0.07 ( - 1.32) and 0.60 within the considered redshift range. We do not find any significant evolution in the mean β within our redshift window. Our measurements add new data points to the global β-z relation in the least-explored redshift regime, further reinforcing the gradual reddening of galaxy UV continuum with cosmic time. We notice no strong consistent trend between β and M₁₅₀₀ for the entire luminosity range -21 <M₁₅₀₀ < - 15 mag. However, the majority of the most-luminous galaxies (M₁₅₀₀ < - 19 mag) are found to have relatively redder slopes. Using UVIT, we detect galaxies as faint as M₁₅₀₀ = - 15.6 mag (i.e., 0.028 ${L}_{z=0.5}^{* }$). The faintest galaxies (M₁₅₀₀ > - 16 mag) tend to be redder, which indicates they were less actively forming stars during this cosmic time interval. Our study highlights the unique capability of UVIT near-UV imaging to characterize the rest-frame far-UV properties of galaxies at redshift z ∼ 0.5.