Star formation in IRDC G31.97+0.07
  We utilize multiple-waveband continuum and molecular-line data of CO
isotopes, to study the dynamical structure and physical properties of the IRDC
G31.97+0.07. We derive the dust temperature and H$_2$ column density maps of
the whole structure by SED fitting. The total mass is about
$2.5\times10^5\,M_{\odot}$ for the whole filamentary structure and about
$7.8\times10^4\,M_{\odot}$ for the IRDC. Column density PDFs produced from the
column density map are generally in the power-law form suggesting that this
part is mainly gravity-dominant. The flatter slope of the PDF of the IRDC
implies that it might be compressed by an adjacent, larger \HII region. There
are 27 clumps identified from the 850\,\micron \ continuum located in this
filamentary structure. Based on the average spacing of the fragments in the
IRDC, we estimate the age of the IRDC. The age is about $6.4\,$Myr assuming
inclination angle $i = 30^\circ$. For 18 clumps with relatively strong CO and
$^{13}$CO (3-2) emission, we study their line profiles and stabilities. We find
5 clumps with blue profiles which indicate gas infall motion and 2 clumps with
red profiles which indicate outflows or expansion. Only one clump has
$\alpha_\mathrm{vir} > 2$, suggesting that most clumps are gravitationally
bound and tend to collapse. In the Mass-$R_\mathrm{eq}$ diagram, 23 of 27
clumps are above the threshold for high-mass star formation, suggesting that
this region can be a good place for studying high-mass star-forming.
