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, 41 Planck Galactic Cold Clumps at high Galactic latitude (HGal; ∣b∣ > 25°) were observed in 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 16 clumps. The highest and average latitudes are 71°4 and 37°8, respectively. Fifty-one velocity components were obtained, and then each was identified as a single clump. Thirty-three clumps were further mapped at 1' resolution, and 54 dense cores were extracted. Among dense cores, the average excitation temperature T_ex of ¹²CO is 10.3 K. The average line widths of thermal and nonthermal velocity dispersions are 0.19 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 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 to 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 that bear masses from 0.01 to 1 M_⊙ are gravitationally bound, and all appear to be confined by outer pressure.