13CO in IC 342: Evidence for a Spiral Density Wave in the Nucleus
Abstract
We present high-resolution (5", ~ 40 pc) maps of the ^13^CO emission in the nucleus of the nearby spiral galaxy IC 342. ^13^CO emission, a tracer of the H_2_ density distribution, indicates that the molecular gas in the nucleus takes the form of two spiral arms of total extent 500 pc. Molecular gas constitutes ~10% of the total dynamical mass within the inner half-kiloparsec, increasing to ~ 50% in the inner 100 pc. The intense star formation traced by radio continuum and 10 micron emission is located within 40-50 pc of the dynamical center, where the two molecular ridges meet. Less luminous star-forming regions traced by Hα emission outside the immediate nuclear region follow the outer, convex edges of the CO arms, offset by ~50-100 pc. From the offset of the Hα arms and the CO arms and the strongly radial motions observed in the molecular gas, we interpret the gaseous structure in the nucleus of IC 342 as the response to a spiral density wave. The lack of an inner Lindblad resonance, which is likely in IC 342 because of the slowly rising rotation curve, would allow the continuation of a two-armed spiral density wave far into the nucleus. The high molecular mass fraction suggests that the observed density wave may be gaseous and not stellar. We suggest that streaming motions and dissipative processes along the spiral arms channel the gas into the nucleus, leading to the development of the starburst.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1992
- DOI:
- 10.1086/170852
- Bibcode:
- 1992ApJ...384...72T
- Keywords:
-
- Carbon Monoxide;
- Cosmochemistry;
- Density Wave Model;
- Galactic Nuclei;
- Spiral Galaxies;
- Interstellar Matter;
- Star Formation;
- Astrophysics;
- GALAXIES: INDIVIDUAL ALPHANUMERIC: IC 342;
- GALAXIES: INTERSTELLAR MATTER;
- GALAXIES: NUCLEI;
- GALAXIES: SPIRAL;
- ISM: MOLECULES;
- STARS: FORMATION