117 research outputs found
Variation of Molecular Cloud Properties across the Spiral Arm in M 51
We present the results of high-resolution 13CO(1-0) mapping observations with
the NRO 45m telescope of the area toward the southern bright arm region of M51,
including the galactic center. The obtained map shows the central depression of
the the circumnuclear ring and the spiral arm structure.The arm-to-interarm
ratio of the 13CO(1-0) integrated intensity is 2-4. We also have found a
feature different from that found in the 12CO results. The 12CO/13CO ratio
spatially varies, and shows high values (~20) for the interarm and the central
region, but low values(~10) for the arm. These indicate that there is a denser
gas in the spiral arm than in the interarm. The distribution of the 13CO shows
a better correspondence with that of the H\alpha emission than with the 12CO in
the disk region, except for the central region. We found that the 13CO emission
is located on the downstream side of the 12CO arm, namely there is an offset
between the 12CO and the 13CO as well as the H\alpha emission. This suggests
that there is a time delay between the accumulation of gas caused by the
density wave and dense gas formation, accordingly star formation. This time
delay is estimated to be ~10^7 yr based on the assumption of galactic rotation
derived by the rotation curve and the pattern speed of M51. It is similar to
the growth timescale of a gravitational instability in the spiral arm of M51,
suggesting that the gravitational instability plays an important role for dense
gas formation.Comment: 23 pages, 10 figures, PASJ Vol.54, No.2 (2002), in pres
High Resolution Molecular Gas Maps of M33
New observations of CO (J=1->0) line emission from M33, using the 25 element
BEARS focal plane array at the Nobeyama Radio Observatory 45-m telescope, in
conjunction with existing maps from the BIMA interferometer and the FCRAO 14-m
telescope, give the highest resolution (13'') and most sensitive (RMS ~ 60 mK)
maps to date of the distribution of molecular gas in the central 5.5 kpc of the
galaxy. A new catalog of giant molecular clouds (GMCs) has a completeness limit
of 1.3 X 10^5 M_sun. The fraction of molecular gas found in GMCs is a strong
function of radius in the galaxy, declining from 60% in the center to 20% at
galactocentric radius R_gal ~ 4 kpc. Beyond that radius, GMCs are nearly
absent, although molecular gas exists. Most (90%) of the emission from low mass
clouds is found within 100 pc projected separation of a GMC. In an annulus 2.1<
R_gal <4.1 kpc, GMC masses follow a power law distribution with index -2.1.
Inside that radius, the mass distribution is truncated, and clouds more massive
than 8 X 10^5 M_sun are absent. The cloud mass distribution shows no
significant difference in the grand design spiral arms versus the interarm
region. The CO surface brightness ratio for the arm to interarm regions is 1.5,
typical of other flocculent galaxies.Comment: 14 pages, 14 figures, accepted in ApJ. Some tables poorly typeset in
emulateapj; see source files for raw dat
The Structure, Kinematics and Physical Properties of the Molecular Gas in the Starburst Nucleus of NGC 253
We present 5.2" x 2.6" resolution interferometry of CO J=1-0 emission from
the starburst galaxy NGC 253. The high spatial resolution of these new data, in
combination with recent high resolution maps of 13CO, HCN and near-infrared
emission, allow us for the first time to link unambiguously the gas properties
in the central starburst of NGC 253 with its bar dynamics. We confirm that the
star formation results from bar-driven gas flows as seen in "twin peaks"
galaxies. Two distinct kinematic features are evident from the CO map and
position-velocity diagram: a group of clouds rotating as a solid body about the
kinematic center of the galaxy, and a more extended gas component associated
with the near-infrared bar. We model the line intensities of CO, HCN and 13CO
to infer the physical conditions of the gas in the nucleus of NGC 253. The
results indicate increased volume densities around the radio nucleus in a
twin-peaks morphology. Compared with the CO kinematics, the gas densities
appear highest near the radius of a likely inner Linblad resonance, and
slightly lead the bar minor axis. This result is similar to observations of the
face-on, twin-peaks galaxy NGC 6951, and is consistent with models of starburst
generation due to gas inflow along a bar.Comment: To appear in the ApJ, 28 pages, 12 figure file
Tracing star formation in galaxies with molecular line and continuum observations
We report our recent progress on extragalactic spectroscopic and continuum
observations, including HCN(J=1-0), HCO(J=1-0), and CN(N=1-0) imaging
surveys of local Seyfert and starburst galaxies using the Nobeyama Millimeter
Array, high-J CO observations (J=3-2 observations using the Atacama
Submillimeter Telescope Experiment (ASTE) and J=2-1 observations with the
Submillimeter Array) of galaxies, and 1.1 mm continuum observations
of high-z violent starburst galaxies using the bolometer camera AzTEC mounted
on ASTE.Comment: 6 pages, 5 figures, To appear in proceedings of "Far-Infrared and
Submillimeter Emission of the Interstellar Medium", EAS Publication Series,
Bad Honnef, November 2007, Eds. C. Kramer, S. Aalto, R. Simon. See
http://www.nro.nao.ac.jp/~f0212kk/FIR07/kk-ver20.pdf for a version with high
resolution figure
The 2006 Radio Outburst of a Microquasar Cyg X-3: Observation and Data
We present the results of the multi-frequency observations of radio outburst
of the microquasar Cyg X-3 in February and March 2006 with the Nobeyama 45-m
telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope.
Since the prediction of a flare by RATAN-600, the source has been monitored
from Jan 27 (UT) with these radio telescopes. At the eighteenth day after the
quench of the activity, successive flares exceeding 1 Jy were observed
successfully. The time scale of the variability in the active phase is
presumably shorter in higher frequency bands.
We also present the result of a follow-up VLBI observation at 8.4 GHz with
the Japanese VLBI Network (JVN) 2.6 days after the first rise. The VLBI image
exhibits a single core with a size of <8 mas (80 AU). The observed image was
almost stable, although the core showed rapid variation in flux density. No jet
structure was seen at a sensitivity of K.Comment: 17 pages,6 figures; accepted by PAS
AzTEC/ASTE 1.1-mm Survey of the AKARI Deep Field South: source catalogue and number counts
We present results of a 1.1 mm deep survey of the AKARI Deep Field South
(ADF-S) with AzTEC mounted on the Atacama Submillimetre Telescope Experiment
(ASTE). We obtained a map of 0.25 sq. deg area with an rms noise level of
0.32-0.71 mJy. This is one of the deepest and widest maps thus far at
millimetre and submillimetre wavelengths. We uncovered 198 sources with a
significance of 3.5-15.6 sigma, providing the largest catalog of 1.1 mm sources
in a contiguous region. Most of the sources are not detected in the
far-infrared bands of the AKARI satellite, suggesting that they are mostly at z
~ 1.5 given the detection limits. We constructed differential and cumulative
number counts in the ADF-S, the Subaru/XMM Newton Deep Field (SXDF), and the
SSA 22 field surveyed by AzTEC/ASTE, which provide currently the tightest
constraints on the faint end. The integration of the best-fit number counts in
the ADF-S find that the contribution of 1.1 mm sources with fluxes >=1 mJy to
the cosmic infrared background (CIB) at 1.1 mm is 12-16%, suggesting that the
large fraction of the CIB originates from faint sources of which the number
counts are not yet constrained. We estimate the cosmic star-formation rate
density contributed by 1.1 mm sources with >=1 mJy using the best-fit number
counts in the ADF-S and find that it is lower by about a factor of 5-10
compared to those derived from UV/optically-selected galaxies at z ~ 2-3. The
fraction of stellar mass of the present-day universe produced by 1.1 mm sources
with >=1 mJy at z >= 1 is ~20%, calculated by the time integration of the
star-formation rate density. If we consider the recycled fraction of >0.4,
which is the fraction of materials forming stars returned to the interstellar
medium, the fraction of stellar mass produced by 1.1 mm sources decrease to
<~10%.Comment: 15 pages, 12 figure, accepted for publication in MNRA
Recommended from our members
Enhancing laser beam performance by interfering intense laser beamlets
Increasing the laser energy absorption into energetic particle beams represents a longstanding quest in intense laser-plasma physics. During the interaction with matter, part of the laser energy is converted into relativistic electron beams, which are the origin of secondary sources of energetic ions, γ-rays and neutrons. Here we experimentally demonstrate that using multiple coherent laser beamlets spatially and temporally overlapped, thus producing an interference pattern in the laser focus, significantly improves the laser energy conversion efficiency into hot electrons, compared to one beam with the same energy and nominal intensity as the four beamlets combined. Two-dimensional particle-in-cell simulations support the experimental results, suggesting that beamlet interference pattern induces a periodical shaping of the critical density, ultimately playing a key-role in enhancing the laser-to-electron energy conversion efficiency. This method is rather insensitive to laser pulse contrast and duration, making this approach robust and suitable to many existing facilities
AzTEC/ASTE 1.1-mm survey of the AKARI Deep Field South: source catalogue and number counts
This article has been accepted for publication in Monthly Notices Of The Royal Astronomical Society ©: 2010 K. B. Hatsukade et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present results of a 1.1-mm deep survey of the AKARI Deep Field South (ADF-S) with AzTEC mounted on the Atacama Submillimetre Telescope Experiment (ASTE). We obtained a map of 0.25-deg2 area with an rms noise level of 0.32–0.71 mJy. This is one of the deepest and widest maps thus far at millimetre and submillimetre wavelengths. We uncovered 198 sources with a significance of 3.5σ–15.6σ, providing the largest catalogue of 1.1-mm sources in a contiguous region. Most of the sources are not detected in the far-infrared bands of the AKARI satellite, suggesting that they are mostly at z≥ 1.5 given the detection limits. We constructed differential and cumulative number counts in the ADF-S, the Subaru/XMM–Newton Deep Field and the SSA 22 field surveyed by AzTEC/ASTE, which provide currently the tightest constraints on the faint end. The integration of the best-fitting number counts in the ADF-S finds that the contribution of 1.1-mm sources with fluxes of ≥1 mJy to the cosmic infrared background (CIB) at 1.1 mm is 12–16 per cent, suggesting that the large fraction of the CIB originates from faint sources of which the number counts are not yet constrained. We estimate the cosmic star formation rate density contributed by 1.1-mm sources with ≥1 mJy using the best-fitting number counts in the ADF-S and find that it is lower by about a factor of 5–10 compared to those derived from UV/optically selected galaxies at z∼ 2–3. The fraction of stellar mass of the present-day universe produced by 1.1-mm sources with ≥1 mJy at z≥ 1 is ∼20 per cent, calculated by the time integration of the star formation rate density. If we consider the recycled fraction of >0.4, which is the fraction of materials forming stars returned to the interstellar medium, the fraction of stellar mass produced by 1.1-mm sources decreases to ≲10 per cent
Temperature Variations of the Cold Dust in the Triangulum Galaxy M33
We present wide-field 1.1 mm continuum imaging of the nearby spiral galaxy M
33, conducted with the AzTEC bolometer camera on ASTE. We show that the 1.1 mm
flux traces the distribution of dust with T ~20 K. Combined with far-infrared
imaging at 160um, we derive the dust temperature distribution out to a galactic
radius of ~7 kpc with a spatial resolution of ~100 parsecs. Although the 1.1 mm
flux is observed predominantly near star forming regions, we find a smooth
radial temperature gradient declining from ~20 K to ~13 K, consistent with
recent results from the Herschel satellite. Further comparison of individual
regions show a strong correlation between the cold dust temperature and the Ks
band brightness, but not with the ionizing flux. The observed results imply
that the dominant heating source of cold dust at few hundred parsec scales are
due to the non-OB stars, even when associated with star forming regions.Comment: Accepted for publication in PAS
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