The MOSDEF survey: the dependence of H α-to-UV SFR ratios on SFR and size at z ∼ 2

We perform an aperture-matched analysis of dust-corrected H alpha and UV star formation rates (SFRs) using 303 star-forming galaxies with spectroscopic redshifts 1.36 < z(spec) < 2.66 from the MOSFIRE Deep Evolution Field survey. By combining H alpha and H beta emission line measurements with multiwaveband resolved Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey/3D-HST imaging, we directly compare dust-corrected H alpha and UV SFRs, inferred assuming a fixed attenuation curve shape and constant SFHs, within the spectroscopic aperture. Previous studies have found that Ha and UV SFRs inferred with these assumptions generally agree for typical star-forming galaxies, but become increasingly discrepant for galaxies with higher SFRs (greater than or similar to 100 M-circle dot yr(-1)), with H alpha-to-UV SFR ratios being larger for these galaxies. Our analysis shows that this trend persists even after carefully accounting for the apertures over which H alpha and UV-based SFRs (and the nebular and stellar continuum reddening) are derived. Furthermore, our results imply that Ha SFRs may be higher in the centres of large galaxies (i.e. where there is coverage by the spectroscopic aperture) compared to their outskirts, which could be indicative of inside-out galaxy growth. Overall, we suggest that the persistent difference between nebular and stellar continuum reddening and high H alpha-to-UV SFR ratios at the centres of large galaxies may be indicative of a patchier distribution of dust in galaxies with high SFRs.