PMO Polaris CO survey. I. A 100 deg${}^2$ view of the Polaris Flare

Abstract

Large-area CO surveys are essential for studying molecular cloud dynamics and evolution; however, most have focused on the Galactic plane, leaving high-latitude clouds less explored. We present the PMO Polaris CO Survey (PPCOS), which maps a 100~deg${}^2$ region of the Polaris Flare in the $J=1-0$ transitions of ${}^{12}$CO, ${}^{13}$CO, and C${}^{18}$O using the Delingha 13.7~m telescope. As the first large-area CO survey at high Galactic latitude ($|b|>20^{\circ }$) with sub-arcminute resolution, PPCOS achieves sensitivities of $\sim$0.46~K for ${}^{12}$CO and $\sim$0.23~K for ${}^{13}$CO and C${}^{18}$O at a spectral resolution of 0.16~km~s${}^{-1}$ and an angular resolution of 50\arcsec. The ${}^{12}$CO emission reveals seven distinct complexes, where only $\sim$10\% of pixels display multiple velocity components, alongside a global velocity gradient of 0.18~km~s${}^{-1}$~pc${}^{-1}$. Typical line widths are $1.2\pm 0.6$~\mbox{km~s${}^{-1}$} for ${}^{12}$CO, while ${}^{13}$CO components are systematically narrower ($\lesssim 0.7\hat{I}”V_{{}^{12}\mathrm{CO}}$). The ${}^{12}$CO/${}^{13}$CO intensity ratios (5--25) indicate widespread ${}^{12}$CO optical thickness, resembling conditions found in giant molecular clouds (GMCs). Globally, the CO emission divides into two groups: a major group aligned with the velocity gradient and a secondary group elongated perpendicular to it, possibly regulated by large-scale coherent dynamics. We propose a three-layer hierarchy: a dynamically assembling and dispersing periphery traced by ${}^{12}$CO, a more stable intermediate kernel traced by ${}^{13}$CO, and gravitationally bound compact cores traced by C${}^{18}$O. No young stellar objects are firmly associated with the molecular gas. PPCOS provides an ideal laboratory for studying turbulence, hierarchical structure, and early cloud evolution in a nearby, relatively simple molecular cloud.

22 pages, 19 figures, submitted to A&A