Molecular Gas in Candidate Double-Barred Galaxies II. Cooler, Less Dense Gas Associated with Stronger Central Concentrations

Details Molecular Gas in Candidate Double-Barred Galaxies II. Cooler, Less Dense Gas Associated with Stronger Central Concentrations Molecular Gas in Candidate Double-Barred Galaxies II. Cooler, Less Dense Gas Associated with Stronger Central Concentrations

2003-01-07

arxiv.org/abs/astro-ph/0301116v1

Astrophys.J. 587 (2003) 649-659

Astronomy and Astrophysics

Astrophysics

27 pages + 6 figures; to appear in the April 20, 2003 issue of ApJ

Scientific paper

10.1086/368341

We have performed a multi-transition CO study of the centers of seven double-barred galaxies that exhibit a variety of molecular gas morphologies to determine if the molecular gas properties are correlated with the nuclear morphology and star forming activity. Near infrared galaxy surveys have revealed the existence of nuclear stellar bars in a large number of barred or lenticular galaxies. High resolution CO maps of these galaxies exhibit a wide range of morphologies. Recent simulations of double-barred galaxies suggest that variations in the gas properties may allow it to respond differently to similar gravitational potentials. We find that the 12CO J=3-2/J=2-1 line ratio is lower in galaxies with centrally concentrated gas distributions and higher in galaxies with CO emission dispersed around the galactic center in rings and peaks. The 13CO/12CO J=2-1 line ratios are similar for all galaxies, which indicates that the J=3-2/J=2-1 line ratio is tracing variations in gas temperature and density, rather than variations in optical depth. There is evidence that the galaxies which contain more centralized CO distributions are comprised of molecular gas that is cooler and less dense. Observations suggest that the star formation rates are higher in the galaxies containing the warmer, denser, less centrally concentrated gas. It is possible that either the bar dynamics are responsible for the variety of gas distributions and densities (and hence the star formation rates) or that the star formation alone is responsible for modifying the gas properties.

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