On the temperature structure of the Galactic Centre cloud G0.253+0.016

TL;DR

This study uses hydrodynamical models to analyze the temperature structure of the dense Galactic Centre cloud G0.253+0.016, revealing extreme environmental conditions with high radiation and cosmic ray rates affecting its cooling processes.

Contribution

The paper introduces detailed hydrodynamical modeling of G0.253+0.016, demonstrating the necessity of high interstellar radiation and cosmic ray ionization rates to match observed temperatures.

Findings

ISRF must be about 1000 times solar neighborhood value

CRIR needs to be roughly 1E-14 /s to match observations

Neutral oxygen dominates cooling in the cloud's interior

Abstract

We present a series of smoothed particle hydrodynamical models of G0.253+0.016 (also known as 'The Brick'), a very dense molecular cloud that lies close to the Galactic Centre. We explore how its gas and dust temperatures react as we vary the strength of both the interstellar radiation field (ISRF) and the cosmic ray ionisation rate (CRIR). As the physical extent of G0.253+0.016 along our line-of-sight is unknown, we consider two possibilities: one in which the longest axis is that measured in the plane of the sky (9.4 pc in length), and one in which it is along the line of sight, in which case we take it to be 17 pc. To recover the observed gas and dust temperatures, we find find that the ISRF must be around 1000 times the solar neighbourhood value, and the CRIR must be roughly 1E-14 /s, regardless of the geometries studied. For such high values of the CRIR, we find that cooling in the cloud's interior is dominated by neutral oxygen, in contrast to standard molecular clouds, which at the same densities are mainly cooled via CO. Our results suggest that the conditions near G0.253+0.016 are more extreme than those generally accepted for the inner 500 pc of the galaxy.