Mass estimates for very cold (< 8 K) gas in molecular cloud cores

TL;DR

This study models the temperature distribution of dust in prestellar cores to estimate the fraction of very cold gas (<8 K), revealing that less than 20% of core mass is this cold, with implications for star formation understanding.

Contribution

It provides a detailed modeling approach to estimate the cold gas fraction in cores, considering various environmental and dust properties, which was previously less constrained.

Findings

Less than 20% of core mass is below 8 K in typical conditions.

Higher fractions of very cold gas can occur in specific environments.

Mass uncertainty from dust emission modeling is smaller than from dust opacity uncertainties.

Abstract

The mass of prestellar cores is an essential ingredient to understand the onset of star formation in the core. The low level of emission from cold dust may keep parts of it hidden from observation. We aim to determine the fraction of core mass in the temperature range < 8 K that can be expected for typical low- and high-mass star formation regions. We calculate the dust temperature within standard spherically symmetric prestellar cores for a grid of density powerlaws in the outer core regions, core masses, and variation in the external multi-component radiation field. The dust is assumed to be composed of amorphous silicate and carbon, and variations of its optical properties are discussed. As measure for the distribution of cores and clumps, we use core mass functions derived for various environments. In view of the high densities in very cold central regions, dust and gas temperatures are assumed to be equal. We find that the fraction of mass with temperatures < 8 K in typical low- and high-mass cores is < 20\%. It is possible to obtain higher fractions of very cold gas by placing intermediate- or high-mass cores in a typical low-mass star formation environment. We show that the mass uncertainty arising from FIR to mm modeling of very cold dust emission is smaller than the mass uncertainty due to the unknown dust opacities.