HST H{\alpha} grism spectroscopy of ROLES: a flatter low-mass slope for
  the z~1 SSFR--mass relation
  We present measurements of star formation rates (SFRs) for dwarf galaxies
(M*~10^8.5 Msun ) at z~1 using near-infrared slitless spectroscopy from the
Hubble Space Telescope (HST) by targetting and measuring the luminosity of the
H{\alpha} emission line. Our sample is derived from the Redshift One LDSS3
Emission Line Survey (ROLES), which used [O II]{\lambda} 3727 as a tracer of
star formation to target very low stellar masses down to very low SFRs (~0.1
Msun yr^-1) at this epoch. Dust corrections are estimated using SED-fits and we
find, by comparison with other studies using Balmer decrement dust corrections,
that we require a smaller ratio between the gas phase and stellar extinction
than the nominal Calzetti relation, in agreement with recent findings by other
studies. By stacking the WFC3 spectra at the redshifts obtained from
ground-based [O II] detections, we are able to push the WFC3 spectra to much
lower SFRs and obtain the most complete spectroscopic measurement of the low
mass end of the SSFR--mass relation to date. We measure a flatter low mass
power law slope (-0.47 +/- 0.04) than found by other (shallower)
H{\alpha}-selected samples (\approx -1), although still somewhat steeper than
that predicted by the EAGLE simulation (-0.14 +/- 0.05), hinting at possible
missing physics not modelled by EAGLE or remaining incompleteness for our
H{\alpha} data.
