1,067 research outputs found
Investigating physical states of molecular gas in the overlapping region of interacting galaxies NGC4567/4568 using ALMA
We present ALMA observations of a diffuse gas tracer, CO(J = 1-0), and a
warmer and denser gas tracer, CO(J = 3-2), in the overlapping region of
interacting galaxies NGC 4567/4568, which are in the early stage of
interaction. To comprehend the impact of galaxy interactions on molecular gas
properties, we focus on interacting galaxies during the early stage and study
their molecular gas properties. In this study, we investigate the physical
states of a filamentary molecular structure at the overlapping region, which
was previously reported. Utilising new higher-resolution CO(J = 1-0) data, we
identify molecular clouds within overlapping and disc regions. Although the
molecular clouds in the filament have a factor of two higher an average virial
parameter (0.56+-0.14) than that in the overlapping region (0.28+-0.12) and in
the disc region (0.26+-0.16), all identified molecular clouds are
gravitationally bound. These clouds in the filament also have a larger velocity
dispersion than that in the overlapping region, suggesting that molecular gas
and/or atomic gas with different velocities collide there. We calculate the
ratio of the integrated intensity of CO(J = 3-2) and CO(J = 1-0) (= R3-2/1-0)
on the molecular cloud scale. The maximum R3-2/1-0 is 0.17+-0.04 for all
identified clouds. The R3-2/1-0 of the molecular clouds in the filament is
lower than that of the surrounding area. This result contradicts the
predictions of previous numerical simulations, which suggested that the
molecular gas on the collision front of galaxies is compressed and becomes
denser. Our results imply that NGC 4567/4568 is in a very early stage of
interaction; otherwise, the molecular clouds in the filament would not yet
fulfil the conditions necessary to trigger star formation.Comment: 25 pages, 13 figures, accepted to PAS
13CO(J=1-0) On-the-fly Mapping of the Giant HII Region NGC 604: Variation in Molecular Gas Density and Temperature due to Sequential Star Formation
We present 13CO(J=1-0) line emission observations with the Nobeyama 45-m
telescope toward the giant HII region NGC 604 in the spiral galaxy M 33. We
detected 13CO(J=1-0) line emission in 3 major giant molecular clouds (GMCs)
labeled as GMC-A, B, and C beginning at the north. We derived two line
intensity ratios, 13CO(J=1-0)/12CO(J =1-0), R13/12, and 12CO(J=3-2)/12CO(J
=1-0), R31, for each GMC at an angular resolution of 25" (100 pc). Averaged
values of R13/12 and R31 are 0.06 and 0.31 within the whole GMC-A, 0.11 and
0.67 within the whole GMC-B, and 0.05 and 0.36 within the whole GMC-C,
respectively. In addition, we obtained R13/12=0.09\pm0.02 and R31=0.76\pm0.06
at the 12CO(J=1-0) peak position of the GMC-B. Under the Large Velocity
Gradient approximation, we determined gas density of 2.8 \times10^3 cm^-3 and
kinetic temperature of 33+9-5 K at the 12CO(J=1-0) peak position of the GMC-B.
Moreover, we determined 2.5 \times10^3 cm^-3 and 25\pm2 K as averaged values
within the whole GMC-B. We concluded that dense molecular gas is formed
everywhere in the GMC-B because derived gas density not only at the peak
position of the GMC but also averaged over the whole GMC exceeds 10^3 cm^-3. On
the other hand, kinetic temperature averaged over the whole GM-B, 25 K, is
significantly lower than that at the peak position, 33 K. This is because HII
regions are lopsided to the northern part of the GMC-B, thus OB stars can heat
only the northern part, including the 12CO(J=1-0) peak position, of this GMC.Comment: 16 pages, 7 figures, PASJ in pres
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