Dependence of the IRX-$\beta$ dust attenuation relation on metallicity
  and environment
  We use a sample of star-forming field and protocluster galaxies at z=2.0-2.5
with Keck/MOSFIRE K-band spectra, a wealth of rest-frame UV photometry, and
Spitzer/MIPS and Herschel/PACS observations, to dissect the relation between
the ratio of IR to UV luminosity (IRX) versus UV slope ($\beta$) as a function
of gas-phase metallicity (12+log(O/H)~8.2-8.7). We find no significant
dependence of the IRX-$\beta$ trend on environment. However, we find that at a
given $\beta$, IRX is highly correlated with metallicity, and less correlated
with mass, age, and sSFR. We conclude that, of the physical properties tested
here, metallicity is the primary physical cause of the IRX-$\beta$ scatter, and
the IRX correlation with mass is presumably due to the mass dependence on
metallicity. Our results indicate that the UV attenuation curve steepens with
decreasing metallicity, and spans the full range of slope possibilities from a
shallow Calzetti-type curve for galaxies with the highest metallicity in our
sample (12+log(O/H)~8.6) to a steep SMC-like curve for those with
12+log(O/H)~8.3. Using a Calzetti (SMC) curve for the low (high) metallicity
galaxies can lead to up to a factor of 3 overestimation (underestimation) of
the UV attenuation and obscured SFR. We speculate that this change is due to
different properties of dust grains present in the ISM of low- and
high-metallicity galaxies.
