A submillimetre survey of the kinematics of the Perseus molecular cloud: I. data

TL;DR

This paper presents extensive submillimetre CO observations of the Perseus molecular cloud, introduces a new data processing method, and compares gas and dust tracers to analyze cloud properties and star formation regions.

Contribution

It provides new submillimetre CO data for Perseus, a novel procedure for removing artefacts from HARP data, and insights into the relationship between gas and dust tracers in star-forming regions.

Findings

C18O is optically thin across most of the cloud.

The 13CO/C18O abundance ratio is approximately 7.

Excitation temperatures range from 8 to 30 K, with little correlation to dust temperatures.

Abstract

We present submillimetre observations of the J = 3-2 rotational transition of 12CO, 13CO and C18O across over 600 sq arcmin of the Perseus molecular cloud, undertaken with HARP, a new array spectrograph on the James Clerk Maxwell Telescope. The data encompass four regions of the cloud, containing the largest clusters of dust continuum condensations: NGC 1333, IC348, L1448 and L1455. A new procedure to remove striping artefacts from the raw HARP data is introduced. We compare the maps to those of the dust continuum emission mapped with SCUBA (Hatchell et al. 2005) and the positions of starless and protostellar cores (Hatchell et al. 2007a). No straightforward correlation is found between the masses of each region derived from the HARP CO and SCUBA data, underlining the care that must be exercised when comparing masses of the same object derived from different tracers. From the 13CO/C18O line ratio the relative abundance of the two species ([13CO]/[C18O] ~ 7) and their opacities (typically tau is 0.02-0.22 and 0.15-1.52 for the C18O and 13CO gas respectively) are calculated. C18O is optically thin nearly everywhere, increasing in opacity towards star-forming cores but not beyond tau(C18O)~0.9. Assuming the 12CO gas is optically thick we compute its excitation temperature (around 8-30 K), which has little correlation with estimates of the dust temperature.