Investigating H$\alpha$, UV, and IR star-formation rate diagnostics for a large sample of z ~ 2 galaxies

TL;DR

This study compares Hα, UV, and IR diagnostics for star formation in 262 galaxies at z~2, revealing dust properties and calibrating SFR conversions with implications for understanding galaxy evolution.

Contribution

It provides a detailed comparison of multiple SFR indicators at high redshift and establishes a robust Hα-to-SFR conversion factor independent of dust correction assumptions.

Findings

Hα and UV SFRs agree when assuming equal reddening and Calzetti curve.

Steeper attenuation curves are needed for young galaxies to match IR/UV ratios.

The Hα luminosity to SFR conversion factor aligns with Kennicutt (1998).

Abstract

We use a sample of 262 spectroscopically confirmed star-forming galaxies at redshifts $2.08\leq z\leq 2.51$ to compare H$\alpha$, UV, and IR star-formation-rate diagnostics and to investigate the dust properties of the galaxies. At these redshifts, the H$\alpha$ line shifts to the $K_{s}$-band. By comparing $K_{s}$-band photometry to underlying stellar population model fits to other UV, optical, and near-infrared data, we infer the H$\alpha$ flux for each galaxy. We obtain the best agreement between H$\alpha$- and UV-based SFRs if we assume that the ionized gas and stellar continuum are reddened by the same value and that the Calzetti attenuation curve is applied to both. Aided with MIPS 24$\mu$m data, we find that an attenuation curve steeper than the Calzetti curve is needed to reproduce the observed IR/UV ratios of galaxies younger than 100 Myr. Furthermore, using the bolometric star-formation rate inferred from the UV and mid-IR data (SFR$_{IR}$+SFR$_{UV}$), we calculated the conversion between the H$\alpha$ luminosity and SFR to be $(7.5\pm1.3) \times 10^{-42}$ for a Salpeter IMF, which is consistent with the Kennicutt (1998) conversion. The derived conversion factor is independent of any assumption of the dust correction and is robust to stellar population model uncertainties.