paper

A Multi-Transistion CO Study of the "Antennae" Galaxies NGC4038/9

arXiv:astro-ph/0301126 · doi:10.1086/368353

Abstract

For the Antennae interacting galaxy pair, we have obtained high quality, fully sampled CO J=1-0, 2-1 and 3-2 maps of the regions surrounding the nuclei and the area of overlap between the two galaxies, with an angular resolution of 15" or 1.5 kpc. The CO J=1-0, 2-1, 3-2 emission all peak in the overlap region, which contains ~ 4 x 10^9 solar mass of molecular gas mass if the conventional X factor is used. Line emission at CO J=2-1 and 3-2 is detected at selected points in the two nuclei and the overlap region. Both the ^{12}CO/^{13}CO J=2-1 and 3-2 integrated intensity ratios are remarkably high in the overlap region. This is the first published case in which such high CO/CO J=2-1 and 3-2 ratios are found outside a galactic nucleus. Detailed LVG modeling indicates that the CO and ^{13}CO emission originate in different spatial components. Assuming a CO-to-H2 abundance ratio of , the X factor given by the LVG model is an order of magnitude lower than the conventional value for molecular clouds in the Milky Way. Accordingly, we suggest the possibility that the strong CO emission in the overlap region of the Antennae galaxies is associated with increased radiative efficiency, possibly caused by a large velocity dispersion within the individual molecular clouds. A comparison of the CO J=3-2 emission with the SCUBA 850 um continuum in the Antennae galaxies shows that the CO line emission contributes globally 46% of the 850 um continuum flux and that the ratio of CO J=3-2 to SCUBA 850 um flux varies by a factor of two across the system.

Accepted by ApJ on Jan 2. 2003, and is also available on ApJ preprint site. To download the figures and tables, choose the format "other", then click on the "Download source" at the bottom of the format selector page. Some figures are in png or jpg format to save space

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