The MOSDEF Survey: The strong agreement between H-alpha and UV-to-FIR star formation rates for z~2 star-forming galaxies

Abstract

We present the first direct comparison between Balmer line and panchromatic SED-based SFRs for z~2 galaxies. For this comparison we used 17 star-forming galaxies selected from the MOSFIRE Deep Evolution Field (MOSDEF) survey, with $3σ$ detections for H$α$ and at least two IR bands (Spitzer/MIPS 24$μ$m and Herschel/PACS 100 and 160$μ$m, and in some cases Herschel/SPIRE 250, 350, and 500$μ$m). The galaxies have total IR (8-1000$μ$m) luminosities of $\sim10^{11.4}-10^{12.4}\,\textrm{L}_\odot$ and star-formation rates (SFRs) of $\sim30-250\,\textrm{M}_\odot\,\mathrm{yr^{-1}}$. We fit the UV-to-far-IR SEDs with flexible stellar population synthesis (FSPS) models - which include both stellar and dust emission - and compare the inferred SFRs with the SFR(H$α$,H$β$) values corrected for dust attenuation using Balmer decrements. The two SFRs agree with a scatter of 0.17 dex. Our results imply that the Balmer decrement accurately predicts the obscuration of the nebular lines and can be used to robustly calculate SFRs for star-forming galaxies at z~2 with SFRs up to $\sim200\,\textrm{M}_\odot\,\mathrm{yr^{-1}}$. We also use our data to assess SFR indicators based on modeling the UV-to-mid-IR SEDs or by adding SFR(UV) and SFR(IR), for which the latter is based on the mid-IR only or on the full IR SED. All these SFRs show a poorer agreement with SFR(H$α$,H$β$) and in some cases large systematic biases are observed. Finally, we show that the SFR and dust attenuation derived from the UV-to-near-IR SED alone are unbiased when assuming a delayed exponentially declining star-formation history.