Early Science with the Large Millimetre Telescope: Fragmentation of molecular clumps in the Galaxy

TL;DR

This study uses 1.1 mm dust continuum imaging from the Large Millimeter Telescope to identify and analyze dense molecular cloud fragments, exploring their properties and role in star formation within the Galaxy.

Contribution

It provides a detailed catalog of 1545 compact sources in molecular clouds and investigates their formation mechanisms and relation to star formation thresholds.

Findings

AzTEC sources are high-density peaks within molecular clumps.

Fragment masses are comparable to Jeans' mass for sources within 6 kpc.

Sources linked to star-forming regions exceed critical mass surface densities.

Abstract

Sensitive, imaging observations of the 1.1 mm dust continuum emission from a 1 deg^2 area collected with the AzTEC bolometer camera on the Large Millimeter Telescope are presented. A catalog of 1545 compact sources is constructed based on a Wiener-optimization filter. These sources are linked to larger clump structures identified in the Bolocam Galactic Plane Survey. Hydrogen column densities are calculated for all sources and mass and mean volume densities are derived for the subset of sources for which kinematic distances can be assigned. The AzTEC sources are localized, high density peaks within the massive clumps of molecular clouds and comprise 5-15% of the clump mass. We examine the role of the gravitational instability in generating these fragments by comparing the mass of embedded AzTEC sources to the Jeans' mass of the parent BGPS object. For sources with distances less than 6 kpc the fragment masses are comparable to the clump Jeans' mass, despite having isothermal Mach numbers between 1.6 and 7.2. AzTEC sources linked to ultra-compact HII regions have mass surface densities greater than the critical value implied by the mass-size relationship of infrared dark clouds with high mass star formation while AzTEC sources associated with Class II methanol masers have mass surface densities greater than 0.7 g cm^{-2} that approaches the proposed threshold required to form massive stars.