118 research outputs found
Detection of CO(J=1-0) Emission from Barred Spiral Galaxies at z~0.1
We present the results of CO (J=1-0) observations towards nine barred spiral
galaxies at z=0.08-0.25 using the 45-m telescope at Nobeyama Radio Observatory
(NRO). This survey is the first one specialized for barred spiral galaxies in
this redshift range. We detected CO emission from six out of nine galaxies,
whose CO luminosity (L_CO') ranges (1.09-10.8)\times10^9 K km s^{-1} pc^2.
These are the infrared (IR) dimmest galaxies that have ever been detected in CO
at z~0.1 to date. They follow the L_CO'-L_IR relation among local spiral
galaxies, Luminous Infrared Galaxies (LIRGs), Ultra-Luminous Infrared Galaxies
(ULIRGs) and Sub-millimeter Galaxies (SMGs). Their L_CO' and L_IR are higher
than that of local spiral galaxies which have been detected in CO so far, and
L_IR/L'_CO, which is a measure of star formation efficiency, is comparable to
or slightly higher than that of local ones. This result suggests that these
galaxies are forming stars more actively than local spirals galaxies simply
because they have more fuel.Comment: 9 pages, 5 figures, accepted for publication in PAS
Central Spiral Structure of Molecular Gas in Maffei 2
Distribution and kinematics of molecular gas in the central region of the
barred spiral galaxy Maffei 2 were investigated using a data set of 12CO(1-0),
12CO(2-1), CS(2-1) lines and 103 GHz continuum. We found that the offset ridges
along the kpc-scale bar continue to the central spiral structure embedded in
the weak oval structure which is regarded as x2 orbit in the bar potential. The
spiral structure continues toward the center diverging from the oval structure.
The size of these structures is less than R ~ 100 pc. The mass concentration
within R = 35 pc is estimated to be 2 X 10^8 Mo. The high mass concentration is
consistent with theoretical predictions concerning the creation of such a
nuclear spiral structure. A comparison with the tracers of dense gas and
star-forming region suggests that the dense molecular gas traced by CS(2-1)
line is formed at the crossing points of x1 and x2 orbits and the star-forming
region appears after 2 X 10^5 yr which is comparable with the free-fall time of
the dense gas traced by the CS line (~ 10^5 cm^-3).Comment: 7 pages, 10 figures, Publication of Astronomical Society of Japan, in
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CO (J=1-0) Observation of the cD Galaxy of AWM7: Constraints on the Evaporation of Molecular Gas
We have searched for molecular gas in the cD galaxy of a poor cluster of
galaxies AWM7 using Nobeyama 45 m telescope. We do not detect CO emission in
the galaxy. Our limit of molecular gas in the inner 7.5 kpc is M_H_2< 4 x 10^8
M_sun. We estimate the total mass of molecular gas left in the cD galaxy when
the gas deposited by a cooling flow once becomes molecular gas and the
molecular gas is continuously evaporated by the ambient hot gas. The
observational limit of molecular gas requires f >~ 10^{-3}, where f is the
ratio of the heat conduction rate to that of Spitzer. However, this contradicts
recent X-ray observations showing f<10^{-5}. Thus, the non-detection of CO
cannot be explained by the evaporation, and most of the cooled gas predicted by
a cooling flow model may not change into molecular gas in the cD galaxy.
Moreover, we estimate the evaporation time of molecular clouds brought to a cD
galaxy through the capture of gas-rich galaxies and find that these clouds
should not be evaporated if f <~ 10^{-3}-10^{-4}. Therefore, the non-detection
of CO in a cD galaxy could constrain the total mass of the molecular clouds
brought into it.Comment: 5 pages, 1 figure, to be published in PAS
A Search for Water Masers in the Saturnian System
We searched for H2O 6(1,6)-5(2,3) maser emission at 22.235 GHz from several
Saturnian satellites with the Nobeyama 45m radio telescope in May 2009.
Observations were made for Titan, Hyperion, Enceladus and Atlas, for which
Pogrebenko et al. (2009) had reported detections of water masers at 22.235 GHz,
and in addition for Iapetus and other inner satellites. We detected no emission
of the water maser line for all the satellites observed, although sensitivities
of our observations were comparable or even better than those of Pogrebenko et
al.. We infer that the water maser emission from the Saturnian system is
extremely weak, or sporadic in nature. Monitoring over a long period and
obtaining statistical results must be made for the further understanding of the
water maser emission in the Saturnian system.Comment: 8 pages, 2 figures, accepted for publication in PASJ (Letter
Detection of Molecular Clouds in the Interarm of the Flocculent Galaxy NGC 5055
We present high-resolution (~ 4") 12CO (J = 1 - 0) mapping observations with
high - velocity resolution (~ 2.6 km s^{-1}) toward the disk of flocculent
galaxy NGC 5055, using the Nobeyama Millimeter Array in order to study the
physical properties of the molecular clouds in the arm and the interarm. The
obtained map shows clumpy structures. Although these are mainly distributed
along a spiral arm seen in near-infrared observations, some clouds are located
far from the arm, namely in the interarm. These clouds in both the arm and the
interarm have a typical size and mass of a few 100 pc and a few 10^6 Mo,
respectively. These correspond to the largest Giant Molecular Cloud (GMC) in
our Galaxy, and are slightly smaller than Giant Molecular Associations (GMAs)
in the grand design spiral M 51. Their CO flux-based masses show good agreement
with their virial masses. A size - velocity dispersion relation is also plotted
on an extension of the relation for the Galactic GMCs. These facts suggest that
the properties of these clouds are similar to that of the Galactic GMCs. We
also found no clear systematic offset between the molecular gas and HII regions
unlike M 51. This fact and no existense of GMAs suggest the view that, in NGC
5055, cloud formation and following star formation in both the arm and the
interarm are due to enhancement of gas by local fluctuation. On the other hand,
in grand design spiral galaxies, such as M 51, GMA formations may occur only in
the arm due to a strong density wave also enhanced star formation in GMA
formation may also occur. These may control the optical morphology of spiral
arms in spiral galaxies.Comment: 16 pages, 8 figure
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