Distances to molecular clouds in the second Galactic quadrant

TL;DR

This paper measures distances to 76 molecular clouds in the second Galactic quadrant using Gaia data and clustering algorithms, revealing a large-scale structure at about 1 kpc and providing new distance estimates for most clouds.

Contribution

First accurate distance measurements for 73 molecular clouds in the second Galactic quadrant using a novel combination of clustering and extinction-parallax methods.

Findings

Distances range from 211 to 2631 pc.

A large-scale molecular cloud is coherent at about 1 kpc.

The large cloud spans approximately 700 pc in longitude.

Abstract

We present distances to 76 medium-sized molecular clouds and an extra large-scale one in the second Galactic quadrant ($104.75^\circ <l<150.25^\circ $ and $|b|<5.25^\circ$), 73 of which are accurately measured for the first time. Molecular cloud samples are drawn from $l$-$b$-$V$ space ($-95 < V_{\rm LSR}< 25$ \kms) with the density-based spatial clustering of applications with noise (DBSCAN) algorithm, and distances are measured with the background-eliminated extinction-parallax (BEEP) method using extinctions and Gaia DR2 parallaxes. The range of measured distances to 76 molecular clouds is from 211 to 2631 pc, and the extra large-scale molecular cloud appears to be a coherent structure at about 1 kpc, across about 40\deg\ ($\sim$700 pc) in the Galactic longitude.