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 ($M_{\ast }$) and UV spectral slope (${\hat{I}}^2$) in 33 lensed, low-mass star-forming galaxies at $1.4\le z\le 2.6$, using Keck/MOSFIRE rest-frame optical spectroscopy. Located behind three massive lensing galaxy clusters Abell 1689, MACS J1149.5+2223, and MACS J0717.5+3745, galaxies in our sample have a median stellar mass of $\log (M_{\ast }/M_{\odot })=8.3$ and an intrinsic UV absolute magnitude range of $-20.9<M_{UV}<-13$. We measure nebular dust attenuation via Balmer optical depth ($\ddot{I}{„}_B$) defined as the H$\hat{I}\pm$/H${\hat{I}}^2$ ratio. We also derive physical properties from Hubble Space Telescope multi-wavelength photometry and construct composite spectra using median stacking in bins of $M_{\ast }$ and ${\hat{I}}^2$. We find that the $\ddot{I}{„}_B-{\hat{I}}^2$ relation for the dwarf galaxies in this study is best represented by 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, $E(B-V{)}_{nebular}-M_{\ast }$, down to $\log (M_{\ast }/M_{\odot })\sim 7$. We demonstrate that this relation does not notably evolve with redshift and is consistent with what has been observed for local SDSS galaxies at similar low stellar masses.

18 pages, 8 figures, 1 table