Atomic carbon [C I](3P1-3P0) mapping of the nearby galaxy M 83
Abstract
Atomic carbon (C I) has been proposed to be a global tracer of the molecular gas as a substitute for CO, however, its utility remains unproven. To evaluate the suitability of C I as the tracer, we performed [C I](3P1-3P0) [hereinafter [C I](1-0)] mapping observations of the northern part of the nearby spiral galaxy M 83 with the Atacama Submillimeter Telescope Experiment (ASTE) telescope and compared the distributions of [C I](1-0) with CO lines [CO(1-0), CO(3-2), and 13CO(1-0)], H I, and infrared (IR) emission (70, 160, and 250 μm). The [C I](1-0) distribution in the central region is similar to that of the CO lines, whereas [C I](1-0) in the arm region is distributed outside the CO. We examined the dust temperature, Tdust, and dust mass surface density, Σdust, by fitting the IR continuum-spectrum distribution with a single-temperature modified blackbody. The distribution of Σdust shows a much better consistency with the integrated intensity of CO(1-0) than with that of [C I](1-0), indicating that CO(1-0) is a good tracer of the cold molecular gas. The spatial distribution of the [C I] excitation temperature, Tex, was examined using the intensity ratio of the two [C I] transitions. An appropriate Tex at the central, bar, arm, and inter-arm regions yields a constant [C]$/$[H2] abundance ratio of ~7 × 10-5 within a range of 0.1 dex in all regions. We successfully detected weak [C I](1-0) emission, even in the inter-arm region, in addition to the central, arm, and bar regions, using spectral stacking analysis. The stacked intensity of [C I](1-0) is found to be strongly correlated with Tdust. Our results indicate that the atomic carbon is a photodissociation product of CO, and consequently, compared to CO(1-0), [C I](1-0) is less reliable in tracing the bulk of "cold" molecular gas in the galactic disk.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- June 2021
- DOI:
- 10.1093/pasj/psab020
- arXiv:
- arXiv:2103.03876
- Bibcode:
- 2021PASJ...73..552M
- Keywords:
-
- galaxies: individual (M 83);
- galaxies: ISM;
- gravitational lensing: weak;
- ISM: molecules;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 14 pages, 11 figures, Accepted for publication in PASJ