The Bolocam Galactic Plane Survey. XII. Distance Catalog Expansion Using Kinematic Isolation of Dense Molecular Cloud Structures With 13CO(1-0)

TL;DR

This paper expands the distance catalog for molecular cloud structures in the Galactic plane using a new method that combines 13CO data with Bayesian techniques, significantly increasing the number of well-constrained distances and mapping Galactic structure.

Contribution

It introduces a novel approach for integrating 13CO(1-0) data into Bayesian distance estimation, enhancing the accuracy and scope of molecular cloud distance catalogs.

Findings

Expanded catalog with 1,710 sources, tripling previous data

Approximately 95% velocity agreement between dense gas tracers and 13CO

Well-constrained distances for 20% of sources, mostly within 6 kpc of the Sun

Abstract

We present an expanded distance catalog for 1,710 molecular cloud structures identified in the Bolocam Galactic Plane Survey (BGPS) version 2, representing a nearly threefold increase over the previous BGPS distance catalog. We additionally present a new method for incorporating extant data sets into our Bayesian distance probability density function (DPDF) methodology. To augment the dense-gas tracers (e.g., HCO+(3-2), NH3(1,1)) used to derive line-of-sight velocities for kinematic distances, we utilize the Galactic Ring Survey 13CO(1-0) data to morphologically extract velocities for BGPS sources. The outline of a BGPS source is used to select a region of the GRS 13CO data, along with a reference region to subtract enveloping diffuse emission, to produce a line profile of 13CO matched to the BGPS source. For objects with a HCO+(3-2) velocity, \approx 95% of the new 13CO(1-0) velocities agree with that of the dense gas. A new prior DPDF for kinematic distance ambiguity (KDA) resolution, based on a validated formalism for associating molecular cloud structures with known objects from the literature, is presented. We demonstrate this prior using catalogs of masers with trigonometric parallaxes and HII regions with robust KDA resolutions. The distance catalog presented here contains well-constrained distance estimates for 20% of BGPS V2 sources, with typical distance uncertainties \lesssim 0.5 kpc. Approximately 75% of the well-constrained sources lie within 6 kpc of the Sun, concentrated in the Scutum-Centarus arm. Galactocentric positions of objects additionally trace out portions of the Sagittarius, Perseus, and Outer arms in the first and second Galactic quadrants, and we also find evidence for significant regions of interarm dense gas.