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

Abstract

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.

arXiv comment27 pages + 6 figures; to appear in the April 20, 2003 issue of ApJ

References in corpus (8)

• Star Formation in Galaxies Along the Hubble Sequence
• Bar-driven Transport of Molecular Gas to Galactic Centers and Its Consequences
• Gas Inflow in Barred Galaxies - Effects of Secondary Bars
• Dense Molecular Gas Associated with the Circumnuclear Star Forming Ring in the Barred Spiral Galaxy NGC 6951
• A gas-rich nuclear bar fuelling a powerful central starburst in NGC 2782
• Non-circular Gas Kinematics and Star Formation in the Ringed Galaxy NGC 4736
• Molecular Gas in Candidate Double Barred Galaxies I. The Diverse Morphology and Dynamics of NGC 2273 and NGC 5728
• Temperature and Density Gradients Across the Nucleus of M82

Cited by in corpus (15)

• Double-Barred Galaxies: I. A Catalog of Barred Galaxies with Stellar Secondary Bars and Inner Disks
• [CII] 158$\mu$m Emission and Metallicity in PDRs
• The Fueling and Evolution of AGN: Internal and External Triggers
• The Self-Regulated Growth of Supermassive Black Holes
• An Extragalactic 12CO J=3-2 survey with the Heinrich-Hertz-Telescope
• Structure and kinematics of candidate double-barred galaxies
• Physical properties of the circumnuclear starburst ring in the barred Galaxy NGC 1097
• Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors
• Nuclear Bar Catalyzed Star Formation: 13^CO, C18^O and Molecular Gas Properties in the Nucleus of Maffei 2
• Molecular Gas in SAURON Early-Type Galaxies: Detection of 13CO and HCN Emission
• Dissecting the origin of the submillimeter emission in nearby galaxies with Herschel and LABOCA
• Interferometric 12CO(J=2-1) image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097
• Searching for molecular gas in/outflows in the nuclear regions of five Seyfert galaxies
• Molecular Gas in Candidate Double Barred Galaxies III. A Lack of Molecular Gas?
• Physical Condition of Molecular Gas at the Centre of NGC 1097