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 _ { \text { IR } } +SFR _ { \text { UV } } ) , we calculated the conversion between the H \alpha luminosity and SFR to be ( 7.5 \pm 1.3 ) \times 10 ^ { -42 } for a Salpeter IMF , which is consistent with the Kennicutt ( 23 ) conversion .
The derived conversion factor is independent of any assumption of the dust correction and is robust to stellar population model uncertainties .