Abstract
The nature of dust in distant galaxies is not well understood, and until
recently few direct dust measurements have been possible. We investigate dust
in distant star-forming galaxies using near-infrared grism spectra of the
3D-HST survey combined with archival multi-wavelength photometry. These data
allow us to make a direct comparison between dust towards star-forming regions
(measured using Balmer decrements) and the integrated dust properties (derived
by comparing spectral energy distributions SEDs with stellar population and
dust models) for a statistically significant sample of distant galaxies. We
select a sample of 163 galaxies between 1.36 $łe$ z $łe$ 1.5 with H$\alpha$
SNR $\ge$ 5 and measure Balmer decrements from stacked spectra. First, we stack
spectra in bins of integrated stellar dust attenuation, and find that there is
extra dust extinction towards star-forming regions ($A_V,HII$ is 1.81 times
the integrated $A_V,star$), though slightly lower than found for low-redshift
starburst galaxies. Next, we stack spectra in bins of specific star formation
rate (log sSFR), star formation rate (log SFR), and stellar mass (log M*). We
find that on average $A_V,HII$ increases with SFR and mass, but decreases
with increasing sSFR. The amount of extra extinction also decreases with
increasing sSFR and decreasing stellar mass. Our results are consistent with
the two-phase dust model -- in which galaxies contain both a diffuse and a
stellar birth cloud dust component -- as the extra extinction will increase
once older stars outside the star-forming regions become more dominant.
Finally, using our Balmer decrements we derive dust-corrected H$\alpha$ SFRs,
and find evidence that SED fitting produces incorrect SFRs if very rapidly
declining SFHs are included in the explored parameter space.
Description
[1310.4177] Direct measurement of dust attenuation in z~1.5 star-forming galaxies from 3D-HST: Implications for dust geometry and star formation rates
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