184 research outputs found
Testing the ACA Phase Correction Scheme using the SMA
We conducted the observational tests of a phase correction scheme for the
Atacama Compact Array (ACA) of the Atacama Large Millimeter and submillimeter
Array (ALMA) using the Submillimeter Array (SMA). Interferometers at
millimeter- and submillimeter-wave are highly affected by the refraction
induced by water vapor in the troposphere, which results as phase fluctuations.
The ACA is planning to compensate the atmospheric phase fluctuations using the
phase information of the outermost antennas with interpolating to the inner
antennas by creating a phase screen. The interpolation and extrapolation phase
correction schemes using phase screens are tested with the SMA to study how
effective these schemes are. We produce a plane of a wavefront (phase screen)
from the phase information of three antennas for each integration, and this
phase screen is used for the interpolation and extrapolation of the phases of
inner and outer antennas, respectively. The interpolation scheme obtains
apparently improved results, suggesting that the ACA phase correction scheme
will work well. On the other hand, the extrapolation scheme often does not
improve the results. After the extrapolation, unexpectedly large phase
fluctuations show up to the antennas at the distance of ~140 m away from the
center of the three reference antennas. These direction vectors are almost
perpendicular to the wind direction, suggesting that the phase fluctuations can
be well explained by the frozen phase screen.Comment: 11 pages, 11 figures. Accepted for publication in PAS
FTS Measurements of Submillimeter-Wave Atmospheric Opacity at Pampa la Bola III. Water Vapor, Liquid Water, and 183 GHz Water Vapor Line Opacities
Further analysis has been made on the millimeter and submillimeter-wave
(100-1600 GHz or 3 mm - 188 micron) atmospheric opacity data taken with the
Fourier Transform Spectrometer (FTS) at Pampa la Bola, 4800 m above sea level
in northern Chile, which is the site of the Atacama Large
Millimeter/submillimeter Array (ALMA). Time-sequence plots of millimeter and
submillimeter-wave opacities show similar variations to each other, except for
during the periods with liquid water (fog or clouds) in the atmosphere. Using
millimeter and submillimeter-wave opacity correlations under two conditions,
which are affected and not affected by liquid water, we succeeded to separate
the measured opacity into water vapor and liquid water opacity components. The
water vapor opacity shows good correlation with the 183 GHz water vapor line
opacity, which is also covered in the measured spectra. On the other hand, the
liquid water opacity and the 183 GHz line opacity show no correlation. Since
only the water vapor component is expected to affect the phase of
interferometers significantly, and the submillimeter-wave opacity is less
affected by the liquid water component, it may be possible to use the
submillimeter-wave opacity for a phase-correction of submillimeter
interferometers.Comment: 10 pages, 5 figures, PASJ, vol.55, no.1 (2003), in pres
Molecular Gas and Star formation in ARP 302
We present the Submillimeter Array observation of the CO J=2-1 transition
towards the northern galaxy, ARP 302N, of the early merging system, ARP 302.
Our high angular resolution observation reveals the extended spatial
distribution of the molecular gas in ARP 302N. We find that the molecular gas
has a very asymmetric distribution with two strong concentrations on either
side of the center together with a weaker one offset by about 8 kpc to the
north. The molecular gas distribution is also found to be consistent with that
from the hot dust as traced by the 24 micro continuum emission observed by the
Spitzer. The line ratio of CO J=2-1/1-0 is found to vary strongly from about
0.7 near the galaxy center to 0.4 in the outer part of the galaxy. Excitation
analysis suggests that the gas density is low, less than 10 cm, over
the entire galaxy. By fitting the SED of ARP 302N in the far infrared we obtain
a dust temperature of =26-36 K and a dust mass of M=2.0--3.6 M. The spectral index of the radio
continuum is around 0.9. The spatial distribution and spectral index of the
radio continuum emission suggests that most of the radio continuum emission is
synchrotron emission from the star forming regions at the nucleus and
ARP302N-cm. The good spatial correspondance between the 3.6 cm radio continuum
emission, the Spitzer 8 & 24 m data and the high resolution CO J=2-1
observation from the SMA shows that there is the asymmetrical star forming
activities in ARP 302N.Comment: 19 pages, 8 figures, accepted by A
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
First Detection of A Sub-kpc Scale Molecular Outflow in the Starburst Galaxy NGC 3628
We successfully detected a molecular outflow with a scale of 370-450 pc in
the central region of the starburst galaxy NGC 3628 through deep CO(1-0)
observations by using the Nobeyama Millimeter Array (NMA). The mass of the
outflowing molecular gas is ~2.8x10^7 M_sun, and the outflow velocity is
~90(+/-10) km s^{-1}. The expansion timescale of the outflow is 3.3-6.8 Myr,
and the molecular gas mass flow rate is 4.1-8.5 M_sun yr^{-1}. It requires
mechanical energy of (1.8-2.8)x10^{54} erg to create this sub-kpc scale
molecular outflow. In order to understand the evolution of the molecular
outflow, we compare the physical properties between the molecular outflow
observed from our NMA CO(1-0) data and the plasma gas from the soft X-ray
emission of the Chandra X-ray Observatory (CXO) archival data. We found that
the distribution between the molecular outflow and the strong plasma outflow
seems to be in a similar region. In this region, the ram pressure and the
thermal pressure of the plasma outflow are 10^{-(8-10)} dyne cm^{-2}, and the
thermal pressure of molecular outflow is 10^{-(11-13)} dyne cm^{-2}. This
implies the molecular outflow is still expanding outward. The molecular gas
consumption timescale is estimated as 17-27 Myr, and the total starburst
timescale is 20-34 Myr. The evolutionary parameter is 0.11-0.25, suggesting
that the starburst activity in NGC 3628 is still in a young stage.Comment: 15 pages, 14 figures, accepted by Ap
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