We use a newly assembled large sample of 3,545 star-forming galaxies with secure spectroscopic , grism , and photometric redshifts at z = 1.5 - 2.5 to constrain the relationship between UV slope ( \beta ) and dust attenuation ( L _ { IR } / L _ { UV } \equiv { IRX } ) .
Our sample benefits from the combination of deep Hubble WFC3/UVIS photometry from the Hubble Deep UV ( HDUV ) Legacy survey and existing photometric data compiled in the 3D-HST survey .
Our sample significantly extends the range of UV luminosity and \beta probed in previous samples of UV-selected galaxies , including those as faint as M _ { 1600 } = -17.4 ( \simeq 0.05 L ^ { \ast } _ { UV } ) and having -2.6 \lesssim \beta \lesssim 0.0 .
IRX is measured using stacks of deep Herschel /PACS 100 and 160 \mu m data , and the results are compared with predictions of the IRX- \beta relation for different assumptions of the stellar population model and dust obscuration curve .
Stellar populations with intrinsically blue UV spectral slopes necessitate a steeper attenuation curve in order reproduce a given IRX- \beta relation .
We find that z = 1.5 - 2.5 galaxies have an IRX- \beta relation that is consistent with the predictions for an SMC extinction curve if we invoke sub-solar ( 0.14 Z _ { \odot } ) metallicity models that are currently favored for high-redshift galaxies , while the commonly assumed starburst attenuation curve over-predicts the IRX at a given \beta by a factor of \gtrsim 3 .
The IRX of high-mass M _ { \ast } > 10 ^ { 9.75 } M _ { \odot } galaxies is a factor of > 4 larger than that of low-mass galaxies , lending support for the use of stellar mass as a proxy for dust attenuation .
Separate IRX- L _ { UV } relations for galaxies with blue and red \beta conflate to give an average IRX that is roughly constant with UV luminosity for L _ { UV } \gtrsim 3 \times 10 ^ { 9 } L _ { \odot } .
Thus , the commonly observed trend of fainter galaxies having bluer \beta may simply reflect bluer intrinsic UV slopes for such galaxies , rather than lower dust obscurations .
Taken together with previous studies , we find that the IRX- \beta distribution for young and low-mass galaxies at z \gtrsim 2 implies a dust curve that is steeper than that of the SMC , suggesting a lower dust attenuation for these galaxies at a given \beta relative to older and more massive galaxies .
The lower dust attenuations and higher ionizing photon output implied by low metallicity stellar population models point to Lyman continuum production efficiencies , \xi _ { ion } , that may be elevated by a factor of \approx 2 relative to the canonical value for L ^ { \ast } galaxies , aiding in their ability to keep the universe ionized at z \sim 2 .