The relation between HI Gas and Star Formation Properties in Nearby
  Galaxies
  In this paper, we present some correlations of neutral hydrogen HI gas and
physical properties of galaxies to investigate the role of atomic gas in
governing galaxy evolution. We build a HI-detected sample including 70 galaxies
that are detected by ALFALFA in a 15 deg$^2$ region, and derive their star
formation distribution based on the images of $\rm H\alpha$ narrow-band
observed here. In general, HI-detected galaxies have low surface density of
stellar mass and active star formation. Additionally, most of the galaxies are
in good agreement with the star-forming main sequence, consistent with the
previous findings. We confirm the dependence of star formation (SF) in galaxies
on HI gas at least on global scale, i.e., star formation rate (SFR) generally
increases with HI mass, specific star formation rate (SSFR$\equiv$SFR/M$_*$)
increases with HI fraction ($f_{HI}$) even for a given stellar mass, and
\hi-based star formation efficiency (SFE) mildly increases with the stellar
mass and SFR surface density. Based on the distribution of stellar mass and
star formation, we calculate the morphology indices of the sample, and analyze
the dependence of $f_{HI}$ and SFE on them. The weak correlations between SFE
and morphological indexes imply a weak physical link between HI and star
formation in small scale. We find that $f_{HI}$ mildly increases with the
asymmetry and decreases with the concentration of galaxies, suggesting that the
HI gas supply and its effect are likely correlated with external processes in
the extended disks of galaxies.
