PAMS: The Perseus Arm Molecular Survey-I. Survey description and first results

Abstract

The external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in <inline-formula><tex-math id=TM0001 notation=LaTeX>$^{12}$</tex-math></inline-formula>CO, <inline-formula><tex-math id=TM0002 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO, and C<inline-formula><tex-math id=TM0003 notation=LaTeX>$^{18}$</tex-math></inline-formula>O (J = 3-2). With a survey area of <inline-formula><tex-math id=TM0005 notation=LaTeX>$\sim$</tex-math></inline-formula>8 deg<inline-formula><tex-math id=TM0006 notation=LaTeX>$^2$</tex-math></inline-formula>, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at <inline-formula><tex-math id=TM0007 notation=LaTeX>$\ell \approx 110^{\circ }$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0008 notation=LaTeX>$\ell \approx 135^{\circ }$</tex-math></inline-formula>. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of <inline-formula><tex-math id=TM0009 notation=LaTeX>$T_\mathrm{mb}= 0.7$</tex-math></inline-formula>-1.0 K in 0.3 km s<inline-formula><tex-math id=TM0010 notation=LaTeX>$^{-1}$</tex-math></inline-formula> channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H<inline-formula><tex-math id=TM0011 notation=LaTeX>$_2$</tex-math></inline-formula> column density from Herschel, we calculate representative values for the CO-to-H<inline-formula><tex-math id=TM0012 notation=LaTeX>$_2$</tex-math></inline-formula> column-density X-factors, which are <inline-formula><tex-math id=TM0014 notation=LaTeX>$X_\mathrm{^{12}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0015 notation=LaTeX>$\, =4.0\times 10^{20}$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0016 notation=LaTeX>$X_\mathrm{^{13}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0017 notation=LaTeX>$\, =4.0\times 10^{21}$</tex-math></inline-formula> cm<inline-formula><tex-math id=TM0018 notation=LaTeX>$^{-2}$</tex-math></inline-formula> (K km s<inline-formula><tex-math id=TM0019 notation=LaTeX>$^{-1}$</tex-math></inline-formula>)<inline-formula><tex-math id=TM0020 notation=LaTeX>$^{-1}$</tex-math></inline-formula> with a factor of 1.5 uncertainty. We find that the emission profiles, size-linewidth, and mass-radius relationships of <inline-formula><tex-math id=TM0021 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the X-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.