116 research outputs found
Discovery of Luminous Star Formation in PMN1452-5910/IRAS14482-5857: the Pterodactyl Nebula
We present sensitive 1-3 GHz ATCA radio continuum observations of the
hitherto unresolved star forming region known as either IRAS14482-5857 or
PMN1452-5910. At radio continuum frequencies, this source is characterised by a
"filled-bubble" structure reminiscent of a classical HII region, dominated by
three point sources, and surrounded by low-surface-brightness emission out to
the source extent observed at other frequencies in the literature.
The infrared emission corresponds well to the radio emission, with polycyclic
aromatic hydrocarbon emission surrounding regions of hot dust towards the radio
bubbles. A bright 4.5 m point source is seen towards the centre of the
radio source, suggesting a young stellar object. There is also a linear,
outflow-like structure radiating brightly at 8 and 24 m towards the
brightest peak of the radio continuum. In order to estimate the distance to
this source, we have used Mopra Southern Galactic Plane CO Survey
CO(1-0) and CO(1-0) molecular line emission data.
Integrated-intensity, velocity at peak intensity and line-fitting of the
spectra all point towards the peak centred at =-1.1 km/s being
connected to this cloud. This infers a distance to this cloud of ~12.7 kpc.
Assuming this distance, we estimate a column density and mass towards
IRAS14482-5857 of ~ cm and ,
implying that this source is a site of massive star formation. Reinforcing this
conclusion, our broadband spectral fitting infers dust temperatures of 19 and
110K, emission measures for the sub-pc radio point-source of emission measure
pc cm, electron densities of cm
and photon ionisation rates of s. The evidence
strongly suggests that IRAS14482-5857 is a distant, and hence intense site of
massive star-formation.Comment: 11 pages, 12 figures, accepted for publication in the Astronomical
Journa
Arc-minute-scale studies of the interstellar gas towards HESSJ1804216: Still an unidentified TeV -ray source
The Galactic TeV -ray source HESSJ1804216 is currently an
unidentified source. In an attempt to unveil its origin, we present here the
most detailed study of interstellar gas using data from the Mopra Southern
Galactic Plane CO Survey, 7 and 12mm wavelength Mopra surveys and Southern
Galactic Plane Survey of HI. Several components of atomic and molecular gas are
found to overlap HESSJ1804216 at various velocities along the line of
sight. The CS(1-0) emission clumps confirm the presence of dense gas. Both
correlation and anti-correlation between the gas and TeV -ray emission
have been identified in various gas tracers, enabling several origin scenarios
for the TeV -ray emission from HESSJ1804216. For a hadronic
scenario, SNRG8.70.1 and the progenitor SNR of PSRJ18032137
require cosmic ray (CR) enhancement factors of times the
solar neighbour CR flux value to produce the TeV -ray emission.
Assuming an isotropic diffusion model, CRs from both these SNRs require a slow
diffusion coefficient, as found for other TeV SNRs associated with adjacent ISM
gas. The morphology of gas located at 3.8kpc (the dispersion measure
distance to PSRJ18032137) tends to anti-correlate with features of the
TeV emission from HESSJ1804216, making the leptonic scenario possible.
Both pure hadronic and pure leptonic scenarios thus remain plausible.Comment: 29 pages, 23 figures, 5 tables, accepted for publication in PAS
Probing the local environment of the supernova remnant HESS J1731-347 with CO and CS observations
The shell-type supernova remnant HESS J1731 − 347 emits TeV gamma-rays, and is a key object for the study of the cosmic ray acceleration potential of supernova remnants. We use 0.5–1 arcmin Mopra CO/CS(1–0) data in conjunction with HI data to calculate column densities towards the HESS J1731 − 347 region. We trace gas within at least four Galactic arms, typically tracing total (atomic+molecular) line-of-sight H column densities of 2–3× 10²² cm⁻². Assuming standard X-factor values and that most of the HI/CO emission seen towards HESS J1731 − 347 is on the near-side of the Galaxy, X-ray absorption column densities are consistent with HI+CO-derived column densities foreground to, but not beyond, the Scutum–Crux Galactic arm, suggesting a kinematic distance of ∼3.2 kpc for HESS J1731 − 347. At this kinematic distance, we also find dense, infrared-dark gas traced by CS(1–0) emission coincident with the north of HESS J1731 − 347, the nearby HII region G353.43−0.37 and the nearby unidentified gamma-ray source HESS J1729 − 345. This dense gas lends weight to the idea that HESS J1729 − 345 and HESS J1731 − 347 are connected, perhaps via escaping cosmic-rays.N. Maxted, M. Burton, C. Braiding, G. Rowell, H. Sano, F. Voisin, M. Capasso, G. Pühlhofer and Y. Fuku
The Hall effect in star formation
Magnetic fields play an important role in star formation by regulating the
removal of angular momentum from collapsing molecular cloud cores. Hall
diffusion is known to be important to the magnetic field behaviour at many of
the intermediate densities and field strengths encountered during the
gravitational collapse of molecular cloud cores into protostars, and yet its
role in the star formation process is not well-studied. We present a
semianalytic self-similar model of the collapse of rotating isothermal
molecular cloud cores with both Hall and ambipolar diffusion, and similarity
solutions that demonstrate the profound influence of the Hall effect on the
dynamics of collapse.
The solutions show that the size and sign of the Hall parameter can change
the size of the protostellar disc by up to an order of magnitude and the
protostellar accretion rate by fifty per cent when the ratio of the Hall to
ambipolar diffusivities is varied between -0.5 <= eta_H / eta_A <= 0.2. These
changes depend upon the orientation of the magnetic field with respect to the
axis of rotation and create a preferred handedness to the solutions that could
be observed in protostellar cores using next-generation instruments such as
ALMA.
Hall diffusion also determines the strength and position of the shocks that
bound the pseudo and rotationally-supported discs, and can introduce subshocks
that further slow accretion onto the protostar. In cores that are not initially
rotating Hall diffusion can even induce rotation, which could give rise to disc
formation and resolve the magnetic braking catastrophe. The Hall effect clearly
influences the dynamics of gravitational collapse and its role in controlling
the magnetic braking and radial diffusion of the field merits further
exploration in numerical simulations of star formation.Comment: 22 pages, 10 figures, accepted by MNRA
ATLASGAL - properties of a complete sample of Galactic clumps
The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) is an unbiased 870 μm submillimetre survey of the inner Galactic plane (|ℓ| ⊙ at a heliocentric distance of 20 kpc) and includes representative samples of all of the earliest embedded stages of high-mass star formation. Here, we present the first detailed census of the properties (velocities, distances, luminosities and masses) and spatial distribution of a complete sample of ˜8000 dense clumps located in the Galactic disc (5° 4 yr for clump masses ˜1000 M⊙ decreasing to ˜1 × 104 yr for clump masses >10000 M⊙. We find a strong correlation between the fraction of clumps associated with massive stars and peak column density. The fraction is initially small at low column densities, but reaching 100 per cent for column densities above 1023 cm-2; there are no clumps with column densities above this value that are not already associated with massive star formation. All of the evidence is consistent with a dynamic view of star formation wherein the clumps form rapidly and are initially very unstable so that star formation quickly ensues
The Mopra Southern Galactic Plane CO Survey-data release 4-complete survey
We present observations of the Mopra carbon monoxide (CO) survey of the Southern Galactic Plane, covering Galactic longitudes spanning
l = 250◦ (−110◦) to l = 355◦ (−5◦), with a latitudinal coverage of at least |b| 210 deg2. These data have been
taken at 0.6 arcmin spatial resolution and 0.1 km s−1 spectral resolution, providing an unprecedented view of the molecular gas clouds of
the Southern Galactic Plane in the 109–115 GHz J = 1 − 0 transitions of 12CO, 13CO, C18O, and C17O.K. O. Cubuk ... G. Rowell ... et al
- …