SHIELD: Comparing Gas and Star Formation in Low Mass Galaxies
  We analyze the relationships between atomic, neutral hydrogen (HI) and star
formation (SF) in the 12 low-mass SHIELD galaxies. We compare high spectral
(~0.82 km/s/channel) and spatial resolution (physical resolutions of 170 pc -
700 pc) HI imaging from the VLA with H\alpha and far-ultraviolet imaging. We
quantify the degree of co-spatiality between star forming regions and regions
of high HI column densities. We calculate the global star formation
efficiencies (SFE, $\Sigma_{\rm SFR}$ / $\Sigma_{\rm HI}$), and examine the
relationships among the SFE and HI mass, HI column density, and star formation
rate (SFR). The systems are consuming their cold neutral gas on timescales of
order a few Gyr. While we derive an index for the Kennicutt-Schmidt relation of
N ~ 0.68 $\pm$ 0.04 for the SHIELD sample as a whole, the values of N vary
considerably from system to system. By supplementing SHIELD results with those
from other surveys, we find that HI mass and UV-based SFR are strongly
correlated over five orders of magnitude. Identification of patterns within the
SHIELD sample allows us to bin the galaxies into three general categories: 1)
mainly co-spatial HI and SF regions, found in systems with highest peak HI
column densities and highest total HI masses, 2) moderately correlated HI and
SF regions, found in systems with moderate HI column densities, and 3) obvious
offsets between HI and SF peaks, found in systems with the lowest total HI
masses. SF in these galaxies is dominated by stochasticity and random
fluctuations in their ISM.
