7 research outputs found
Dense and Warm Molecular Gas and Warm Dust in Nearby Galaxies
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) single-dish observations
(beam size ~14"-18") toward nearby starburst and non-starburst galaxies using
the Nobeyama 45 m telescope. The 13CO(1-0) and HCN(1-0) emissions were detected
from all the seven starburst galaxies, with the intensities of both lines being
similar (i.e., the ratios are around unity). On the other hand, for case of the
non-starburst galaxies, the 13CO(1-0) emission was detected from all three
galaxies, while the HCN(1-0) emission was weakly or not detected in past
observations. This result indicates that the HCN/13CO intensity ratios are
significantly larger (~1.15+-0.32) in the starburst galaxy samples than the
non-starburst galaxy samples (<0.31+-0.14). The large-velocity-gradient model
suggests that the molecular gas in the starburst galaxies have warmer and
denser conditions than that in the non-starburst galaxies, and the
photon-dominated-region model suggests that the denser molecular gas is
irradiated by stronger interstellar radiation field in the starburst galaxies
than that in the non-starburst galaxies. In addition, HCN/13CO in our sample
galaxies exhibit strong correlations with the IRAS 25 micron flux ratios. It is
a well established fact that there exists a strong correlation between dense
molecular gas and star formation activities, but our results suggest that
molecular gas temperature is also an important parameter.Comment: 14 pages, 6 figures. Accepted for publication in PAS
Formation of a Massive Black Hole at the Center of the Superbubble in M82
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) interferometric observations
of the central region (about 450 pc in radius) of M82 with the Nobeyama
Millimeter Array, and have successfully imaged a molecular superbubble and
spurs. The center of the superbubble is clearly shifted from the nucleus by 140
pc. This position is close to that of the massive black hole (BH) of >460 Mo
and the 2.2 micron secondary peak (a luminous supergiant dominated cluster),
which strongly suggests that these objects may be related to the formation of
the superbubble. Consideration of star formation in the cluster based on the
infrared data indicates that (1) energy release from supernovae can account for
the kinetic energy of the superbubble, (2) the total mass of stellar-mass BHs
available for building-up the massive BH may be much higher than 460 Mo, and
(3) it is possible to form the middle-mass BH of 100-1000 Mo within the
timescale of the superbubble. We suggest that the massive BH was produced and
is growing in the intense starburst region.Comment: 9 pages, 3 figures, to appear in ApJ Lette
Diffuse and Gravitationally Stable Molecular Gas in the Post-Starburst Galaxy NGC 5195
The Nobeyama Millimeter Array (NMA) has been used to make aperture synthesi