Planck Galactic Cold Clumps at High Galactic Latitude-A Study with CO
  Lines
  Gas at high Galactic latitude is a relatively little-noticed component of the
interstellar medium. In an effort to address this, forty-one Planck Galactic
Cold Clumps at high Galactic latitude (HGal; $|b|>25^{\circ}$) were observed in
$^{12}$CO, $^{13}$CO and C$^{18}$O J=1-0 lines, using the Purple Mountain
Observatory 13.7-m telescope. $^{12}$CO (1-0) and $^{13}$CO (1-0) emission was
detected in all clumps while C$^{18}$O (1-0) emission was only seen in sixteen
clumps. The highest and average latitudes are $71.4^{\circ}$ and
$37.8^{\circ}$, respectively. Fifty-one velocity components were obtained and
then each was identified as a single clump. Thirty-three clumps were further
mapped at 1$^\prime$ resolution and 54 dense cores were extracted. Among dense
cores, the average excitation temperature $T_{\mathrm{ex}}$ of $^{12}$CO is
10.3 K. The average line widths of thermal and non-thermal velocity dispersions
are $0.19$ km s$^{-1}$ and $0.46$ km s$^{-1}$ respectively, suggesting that
these cores are dominated by turbulence. Distances of the HGal clumps given by
Gaia dust reddening are about $120-360$ pc. The ratio of $X_{13}$/$X_{18}$ is
significantly higher than that in the solar neighbourhood, implying that HGal
gas has a different star formation history compared to the gas in the Galactic
disk. HGal cores with sizes from $0.01-0.1$ pc show no notable Larson's
relation and the turbulence remains supersonic down to a scale of slightly
below $0.1$ pc. None of the HGal cores which bear masses from 0.01-1
$M_{\odot}$ are gravitationally bound and all appear to be confined by outer
pressure.
