An analytic column density profile to fit prestellar cores

TL;DR

This paper introduces a new analytical model for fitting the column density profiles of prestellar cores, which is easier to use and provides insights into their dynamical states without assuming equilibrium.

Contribution

The authors develop a three-parameter formula that models prestellar cores' density profiles, allowing for dynamical state analysis without assuming equilibrium or fitting temperature.

Findings

L1689B appears to be collapsing.

B68 is close to hydrostatic equilibrium.

Model fits observed data more easily than Bonnor-Ebert sphere.

Abstract

We present a new analytical three-parameter formula to fit observed column density profiles of prestellar cores. It represents a line-of-sight integral through a spherically symmetric or disc-like isothermal cloud. The underlying model resembles the Bonnor-Ebert model in that it features a flat central region leading into a power-law decline \propto r^{-2} in density, and a well-defined outer radius. However, we do not assume that the cloud is in equilibrium, and can instead make qualitative statements about its dynamical state (expansion, equilibrium, collapse) using the size of the flat region as a proxy. Instead of having temperature as a fitting parameter, our model includes it as input, and thus avoids possible inconsistencies. It is significantly easier to fit to observational data than the Bonnor-Ebert sphere. We apply this model to L1689B and B68. We show that L1689B cannot be in equilibrium but instead appears to be collapsing, while our model verifies that B68 is not far from being a hydrostatic object.