UV Spectral Slope and Nebular Dust Attenuation in Dwarf Galaxies at 1.4 < z < 2.6

Abstract We analyze nebular dust attenuation and its correlation with stellar mass ( M * ) and ultraviolet (UV) spectral slope ( β ) in 33 lensed, low-mass star-forming galaxies at 1.4 ≤ z ≤ 2.6, using Keck/Multi-Object Spectrometer For IR Exploration (MOSFIRE) rest-frame optical spectroscopy. Located behind three massive lensing galaxy clusters A1689, MACS J1149.5+2223, and MACS J0717.5+3745, galaxies in our sample have a median stellar mass of log ( M * / M ⊙ ) = 8.3 and an intrinsic UV absolute magnitude range of −20.9 < M UV < −13. We measure nebular dust attenuation via Balmer optical depth ( τ B ), defined as the H α /H β ratio. We also derive physical properties from Hubble Space Telescope multiwavelength photometry and construct composite spectra using median stacking in bins of M * and β . We find that the τ B – β relation for the dwarf galaxies in this study is best represented by the SMC dust curve. This is consistent with previous studies of low-metallicity galaxies at similar redshifts, which show a steep attenuation curve similar to the SMC curve, in contrast to high-metallicity and more massive galaxies that exhibit a much shallower dust attenuation curve. We also investigate the relationship between nebular dust attenuation and stellar mass, E ( B − V ) nebular − M * , down to log ( M * / M ⊙ ) ∼ 7 . We demonstrate that this relation does not notably evolve with redshift and is consistent with what has been observed for local Sloan Digital Sky Survey (SDSS) galaxies at similar low stellar masses.