Observed UV Continuum Slopes (β) of Galaxies at z = 0.40–0.75 in the GOODS-North Field

Abstract

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 1 σ 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 M _1500 for the entire luminosity range −21 − 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.

Keywords

• High-redshift galaxies
• Galaxy evolution
• Ultraviolet photometry