Paschen-beta Star Formation and Dust Attenuation in Low-Redshift Galaxies

We use Paschen-beta (1282 nm) observations from the Hubble Space Telescope (HST) G141 grism to study the star formation and dust attenuation properties of a sample of 32 low redshift (z < 0.287) galaxies in the CLEAR survey. Many of the galaxies in the sample have significantly higher Pa-beta emission than expected from the star formation rates (SFRs) measured from their (attenuation-corrected) UV continuum or Hα emission, suggesting that Pa-beta is revealing star formation that is otherwise hidden within gas that is optically thick to UV-continuum and Balmer line emission. Galaxies with lower stellar mass tend to have more scatter in their ratio of Pa-beta to attenuation-corrected UV SFRs. When considering our Pa-beta detection limits, this observation is consistent with burstier star formation histories in lower mass galaxies. We also find a large amount of scatter between the nebular dust attenuation measured by Pa-beta/Hα and Hα/Hβ, implying that the Balmer decrement underestimates the attenuation in galaxies across a broad range of stellar mass, morphology, and observed Balmer decrement. Comparing the nebular attenuation from Pa-beta/Hα with the stellar attenuation inferred from the spectral energy distribution, our galaxies are consistent with an average stellar to nebular ratio of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. Together, these results show that Pa-beta is a valuable tracer of a galaxy’s star formation rate, often revealing star formation that is otherwise missed by UV and optical tracers.