Hot Molecular Gas in the Circumnuclear Disk
Abstract
We present an analysis of archival Infrared Space Observatory observations of H2 for three 14\prime\prime × 20\prime\prime pointings in the central 3 pc of the Galaxy: toward the southwest region and northeast region of the Galactic center circumnuclear disk (CND), and toward the supermassive black hole Sgr A*. We detect pure rotational lines from 0-0 S(0) to S(13), as well as a number of rovibrationally excited transitions. Using the pure rotational lines, we perform both fits to a discrete temperature distribution (measuring up to three temperature components with T = 500-600 K, T = 1250-1350 K, and T > 2600 K) and fits to a continuous temperature distribution, assuming a power-law distribution of temperatures. We measure power-law indices of n = 3.22 for the northeast region and n = 2.83 for the southwest region. These indices are lower than those measured for other galaxies or other Galactic center clouds, indicating a larger fraction of gas at high temperatures. We also test whether extrapolating this temperature distribution can yield a reasonable estimate of the total molecular mass, as has been recently done for H2 observations in other galaxies. Extrapolating to a cutoff temperature of 50 K in the southwest (northeast) region, we would measure 32% (140%) of the total molecular gas mass inferred from the dust emission, and 26% (125%) of the total molecular gas mass inferred from the CO emission. Ultimately, the inconsistency of the masses inferred in this way suggests that a simple application of this method cannot yield a reliable estimate of the mass of the CND.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2017
- DOI:
- 10.3847/1538-4357/aa951f
- arXiv:
- arXiv:1701.04826
- Bibcode:
- 2017ApJ...850..192M
- Keywords:
-
- Galaxy: center;
- infrared: ISM;
- ISM: molecules;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 31 pages, 11 figures, ApJ Accepted