High-Density and High-Temperature Circumnuclear Molecular Disk in M51

Details High-Density and High-Temperature Circumnuclear Molecular Disk in M51 High-Density and High-Temperature Circumnuclear Molecular Disk in M51

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...495..267m&link_type=abstract

Astrophysical Journal v.495, p.267

Astronomy and Astrophysics

Astronomy

26

Galaxies: Seyfert, Galaxies: Individual Messier Number: M51, Galaxies: Ism, Galaxies: Nuclei, Ism: Molecules

Scientific paper

We performed high-resolution (5."9 x 5."1) 13CO(1-0) imaging observations of the central region (1.5 kpc in radius) of M51 with the Nobeyama Millimeter Array in order to investigate the physical conditions of the circumnuclear dense molecular clouds. The obtained 13CO image looks very similar to the 12CO image in the sense that the emission is distributed along the inner part of the spiral arms, and there is a conspicuous deficiency of emission at the nucleus, in contrast with the centrally peaked HCN image. The intensity ratio of HCN/13CO obtained in the inner 200 pc is higher than 3 and is almost comparable to those in the circumnuclear molecular gas in the Seyfert galaxy NGC 1068 and in the nuclear region of the prototypical starburst galaxy M82. On the other hand, the 12CO/13CO intensity ratio is ~7 +/- 2 in almost all of the central region, with no enhancement in the nuclear region. The obtained HCN/13CO ratio in the nucleus of M51 was used to derive the physical conditions of the dense molecular gas using the large velocity gradient approximation. Assuming the usual abundance ratio and the velocity gradient of HCN and 13CO, the "inverted" HCN/13CO intensity ratio suggests that the density and the temperature of the circumnuclear molecular gas are as high as 105 cm-3 and greater than 100 K, respectively. As possible origins for these physical conditions, we discuss the interactions between nuclear winds or jets and the interstellar material and compression of interstellar material by supernova driven winds.

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