ON THE TEMPERATURE STRUCTURE OF THE GALACTIC CENTER CLOUD G0.253+0.016

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 center. 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 ionization rate (CRIR). The cloud has an extent in the plane of the sky of roughly 3.4 pc × 9.4 pc. As its size along the line of sight is unknown, we consider two cases. In our fiducial, high-density model, we adopt a depth along the line of sight of 3.4 pc, and in the low-density model we assume an extent along the line of sight of 17 pc. To recover the observed gas and dust temperatures, we find that the ISRF must be around 1000 times the solar neighborhood value, and the CRIR must be roughly 10–14 s–1, 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.