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◦) 42 43 were observed with 12CO, 13CO and C18O J=1-0 lines, using the Purple Mountain Observatory 13.7-m telescope. 12CO (1-0) and 13CO (1-0) emission was detected in all clumps while C18O (1-0) emission was only seen in sixteen clumps. The highest and average latitude for sources detected in this survey are −71.43◦ and 37.8◦, respectively. Fifty-one velocity components were obtained and then each component was identified as a single clump. Thirty-three clumps were further mapped and 54 dense cores were extracted. The emission lines of the cores were studied and the average excitation temperature Tex of 12CO is 10.3 K. The average line width of thermal velocity dispersion and non-thermal velocity dispersion 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 200 pc. The ratio X13/X18 is significantly higher than that in the solar neighborhood, 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 until the scale smaller than 0.1 pc. None of the HGal cores which bear masses from 0.01-1 M⊙ are gravitationally bound and are all confined with outer pressure.