Estimating the Star Formation Rate at 1 kpc Scales in Nearby Galaxies
  Using combinations of H\alpha, ultraviolet (UV), and infrared (IR) emission,
we estimate the star formation rate (SFR) surface density, \Sigma_SFR, at 1 kpc
resolution for 30 disk galaxies that are targets of the IRAM HERACLES CO
survey. We present a new physically-motivated IR spectral energy
distribution-based approach to account for possible contributions to 24\mum
emission not associated with recent star formation. Considering a variety of
"reference" SFRs from the literature, we revisit the calibration of the 24\mum
term in hybrid (UV+IR or H\alpha+IR) tracers. We show that the overall
calibration of this term remains uncertain at the factor of two level because
of the lack of wide-field, robust reference SFR estimates. Within this
uncertainty, published calibrations represent a reasonable starting point for 1
kpc-wide areas of star-forming disk galaxies but we re-derive and refine the
calibration of the IR term in these tracers to match our resolution and
approach to 24\mum emission. We compare a large suite of \Sigma_SFR estimates
and find that above \Sigma_SFR \sim 10^-3 M_\odot yr^-1 kpc^-2 the systematic
differences among tracers are less than a factor of two across two orders of
magnitude dynamic range. We caution that methodology and data both become
serious issues below this level. We note from simple model considerations that
focusing on a part of a galaxy dominated by a single stellar population the
intrinsic uncertainty in H\alpha and FUV-based SFRs are \sim 0.3 and \sim 0.5
dex.
