ASTE CO(3-2) Observations of the Southern Barred Spiral Galaxy NGC 986: a Large Gaseous Bar Filled with a Dense Molecular Medium
Abstract
We present CO(3-2) emission observations toward the 3'×3' (or 20kpc×20kpc at a distance of 23Mpc) region of the southern barred spiral galaxy NGC 986 using the Atacama Submillimeter Telescope Experiment (ASTE). This effort is a part of our on-going extragalactic CO(3-2) imaging project, ADIoS (ASTE Dense gas Imaging of Spiral galaxies). Our CO(3-2) image revealed the presence of a large (the major axis is 14kpc in total length) gaseous bar filled with a dense molecular medium along the dark lanes observed in optical images. This is the largest “dense-gas rich bar” known to date. The dense gas bar, discovered in NGC 986, could be a huge reservoir of possible “fuel” for future starbursts in the central region, and we suggest that star formation in the central region of NGC 986 could still be in a growing phase. We found a good spatial coincidence between the overall distributions of dense molecular gas traced by CO(3-2) and massive star formation depicted by Hα. The global CO(3-2) luminosity, LCO(3-2), of NGC 986 was determined to be (5.4±1.1)×108Kkms-1pc2. The CO(3-2)/CO(1-0) integrated intensity ratio was found to be 0.60±0.13 at a spatial resolution of 44'' or 5kpc, and the CO(3-2)/CO(2-1) ratio was 0.67±0.14 at a beam size of ∼25'' or ∼2.8kpc. These line ratios suggest moderate excitation conditions of CO lines (nH2∼103-4cm-3) in a few kiloparsec region of central NGC 986.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- June 2008
- DOI:
- 10.1093/pasj/60.3.457
- arXiv:
- arXiv:0805.1491
- Bibcode:
- 2008PASJ...60..457K
- Keywords:
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- galaxies: individual (NGC 986);
- galaxies: ISM;
- galaxies: starburst;
- galaxies: structure;
- submillimeter;
- Astrophysics
- E-Print:
- PASJ, in press. See http://www.nro.nao.ac.jp/~f0212kk/00ASTE986CO32/n986-kk45.pdf for a version with full resolution figures