Perseus arm – a new perspective on star formation and spiral structure in our home galaxy

Abstract

Expansion of (sub)millimetre capabilities to high angular resolution offered with interferometers allows to resolve giant molecular clouds (GMCs) in nearby galaxies. This enables us to place the Milky Way in the context of other galaxies to advance our understanding of star foation in our own Galaxy. We, thus, remap 12CO (1-0) data along the Perseus spiral a in the outer Milky Way to a fixed physical resolution and present the first spiral a data cube at a common distance as it would be seen by an observer outside the Milky Way. To achieve this goal, we calibrated the longitude-velocity structure of 12CO gas of the outer Perseus a based on trigonometric distances and maser velocities provided by the BeSSeL survey. The molecular gas data were convolved to the same spatial resolution along the whole spiral a and regridded on to a linear scale map with the coordinate system transfoed to the spiral a reference frame. We deteined the width of the Perseus spiral a to be 7.8 ± 0.2 km s-1 around the kinematic a centre. To study the large-scale structure, we derived the 12CO gas mass surface density distribution of velocities, shifted to the kinematic a centre, and a length. This yields a variation of the gas mass surface density along the a length and a compression of molecular gas mass at linear scale. We deteined a thickness of 63 pc on average for the Perseus spiral a and a centroid of the molecular layer of 8.7 pc.