903 research outputs found
Atomic and Molecular Gas in the Starburst Galaxy NGC4945
Spatial and kinematical correlations between HI and CO (2-1) emission of the
southern spiral galaxy NGC4945 are studied with a common angular (23 arcsec)
and velocity resolution (7 km/s). The 21cm continuum emission is also observed.
The HI kinematics yield a galaxy mass of 1.4x10^{11} Mo within a radius of 380
arcsec, with molecular and neutral atomic gas each contributing 2%. Nuclear HI
absorption at velocities 80 km/s higher than systemic indicates gas flowing
towards the centre. HI features at each end of the major axis (R ~ 600 arcsec)
are interpreted as spiral arms that are viewed tangentially and that also cause
prominent emission features in the radio continuum, HI, and CO further inside
the galaxy. A central elongated region showing non-circular motions is
interpreted as a bar which fuels the nuclear starburst. HI and CO
position-velocity data have been analysed using linear resonance theory and
possible locations of resonances are identified.Comment: 16 pages, Latex file, 9 Postscript Figures, aa.cls and psfig.sty
included. Accepted by Astronomy and Astrophysic
VLA observations of 6-cm excited OH
The VLA was used to determine precise positions for 4765-MHz OH maser
emission sources toward star-forming regions which had been observed about
seven months earlier with the Effelsberg 100-meter telescope. The observations
were successful for K3-50, DR21EX, W75N, and W49A. No line was detected toward
S255: this line had decreased to less than 5 per cent of the flux density
observed only seven months earlier. The time-variability of the observed
features during the past 30 years is summarised. In addition, to compare with
the Effelsberg observations, the 4750-MHz and 4660-MHz lines were observed in
W49A. These lines were found to originate primarily from an extended region
which is distinguished as an exceptional collection of compact continuum
components as well as by being the dynamical centre of the very powerful H_2 O
outflow.Comment: 11 pages, will require MN style file to process. MNRAS, accepted Oct
15, 200
Herschel/HIFI Observations of Hydrogen Fluoride Toward Sagittarius B2(M)
Herschel/HIFI observations have revealed the presence of widespread
absorption by hydrogen fluoride (HF) J = 1-0 rotational transition, toward a
number of Galactic sources. We present observations of HF J = 1-0 toward the
high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a
complex pattern of absorption, with numerous features covering a wide range of
local standard of rest velocities (-130 to 100 km -1). An analysis of this
absorption yields HF abundances relative to H2 of ~1.3 {\times}10-8, in most
velocity intervals. This result is in good agreement with estimates from
chemical models, which predict that HF should be the main reservoir of
gas-phase fluorine under a wide variety of interstellar conditions.
Interestingly, we also find velocity intervals in which the HF spectrum shows
strong absorption features that are not present, or are very weak, in spectra
of other molecules, such as 13CO (1-0) and CS (2-1). HF absorption reveals
components of diffuse clouds with small extinction that can be studied for the
first time. Another interesting observation is that water is significantly more
abundant than hydrogen fluoride over a wide range of velocities toward
Sagittarius B2(M), in contrast to the remarkably constant H2O/HF abundance
ratio with average value close to unity measured toward other Galactic sources
Recent advances using [Cp*Co(CO)I2] catalysts as a powerful tool for C-H functionalisation
Expansion of the synthetic chemists' toolbox is currently a topic of great interest, with successes providing access to novel compounds and more efficient routes towards new and known pharmaceuticals and agrochemicals. In this context, the development and application of first-row transition metal-catalysed C-H functionalisation protocols is seen as a key opportunity. This perspective provides a brief background of the discovery and application of high-valent cobalt-catalysis in C-H functionalisation, before detailing examples of recent advances in this field using the powerful [Cp*Co(CO)I2] catalysts for both terminal couplings and heterocycle formation. Finally, a discussion on the detection and isolation of elusive reactive intermediates in high-valent cobalt-catalysed C-H functionalisation, shedding light on how these catalyst systems operate, will be provided
Synthesis Imaging of Dense Molecular Gas in the N113 HII Region of the Large Magellanic Cloud
We present aperture synthesis imaging of dense molecular gas in the Large
Magellanic Cloud, taken with the prototype millimeter receivers of the
Australia Telescope Compact Array (ATCA). Our observations of the N113 HII
region reveal a condensation with a size of ~6" (1.5 pc) FWHM, detected
strongly in the 1-0 lines of HCO+, HCN and HNC, and weakly in C_2H. Comparison
of the ATCA observations with single-dish maps from the Mopra Telescope and
sensitive spectra from the Swedish-ESO Submillimetre Telescope indicates that
the condensation is a massive clump of ~10^4 solar masses within a larger ~10^5
solar mass molecular cloud. The clump is centered adjacent to a compact,
obscured HII region which is part of a linear structure of radio continuum
sources extending across the molecular cloud. We suggest that the clump
represents a possible site for triggered star formation. Examining the
integrated line intensities as a function of interferometer baseline length, we
find evidence for decreasing HCO+/HCN and HCN/HNC ratios on longer baselines.
These trends are consistent with a significant component of the HCO+ emission
arising in an extended clump envelope and a lower HCN/HNC abundance ratio in
dense cores.Comment: 10 pages, 6 figures, to appear in Ap
H110alpha recombination-line emission and 4.8-GHz continuum emission in the Carina Nebula
We present results from observations of H110alpha recombination-line emission
at 4.874 GHz and the related 4.8-GHz continuum emission towards the Carina
Nebula using the Australia Telescope Compact Array. These data provide
information on the velocity, morphology and excitation parameters of the
ionized gas associated with the two bright HII regions within the nebula, Car I
and Car II. They are consistent with both Car I and Car II being expanding
ionization fronts arising from the massive star clusters Trumpler 14 and
Trumpler 16, respectively. The overall continuum emission distribution at 4.8
GHz is similar to that at lower frequencies. For Car I, two compact sources are
revealed that are likely to be young HII regions associated with triggered star
formation. These results provide the first evidence of ongoing star formation
in the northern region of the nebula. A close association between Car I and the
molecular gas is consistent with a scenario in which Car I is currently carving
out a cavity within the northern molecular cloud. The complicated kinematics
associated with Car II point to expansion from at least two different centres.
All that is left of the molecular cloud in this region are clumps of dense gas
and dust which are likely to be responsible for shaping the striking morphology
of the Car II components.Comment: 10 pages, 7 figures, accepted for publication in MNRA
- âŠ