34 research outputs found
A peculiar jet and arc of molecular gas toward the rich and young stellar cluster Westerlund 2 and a TeV gamma ray source
We have discovered remarkable jet- and arc-like molecular features toward the
rich and young stellar cluster Westerlund2. The jet has a length of ~100 pc and
a width of ~10 pc, while the arc shows a crescent shape with a radius of ~30
pc. These molecular features each have masses of ~10000 solar mass and show
spatial correlations with the surrounding lower density HI gas. The jet also
shows an intriguing positional alignment with the core of the TeV gamma ray
source HESS J1023-575 and with the MeV/GeV gamma-ray source recently reported
by the Fermi collaboration. We argue that the jet and arc are caused by an
energetic event in Westerlund 2, presumably due to an anisotropic supernova
explosion of one of the most massive member stars. While the origin of the TeV
and GeV gamma-ray sources is uncertain, one may speculate that they are related
to the same event via relativistic particle acceleration by strong shock waves
produced at the explosion or by remnant objects such as a pulsar wind nebula or
microquasar
ALMA CO Observations of a Giant Molecular Cloud in M33: Evidence for High-Mass Star Formation Triggered by Cloud-Cloud Collisions
We report the first evidence for high-mass star formation triggered by
collisions of molecular clouds in M33. Using the Atacama Large
Millimeter/submillimeter Array, we spatially resolved filamentary structures of
giant molecular cloud 37 in M33 using CO( = 2-1), CO( =
2-1), and CO( = 2-1) line emission at a spatial resolution of 2
pc. There are two individual molecular clouds with a systematic velocity
difference of 6 km s. Three continuum sources representing up to
10 high-mass stars with the spectral types of B0V-O7.5V are embedded
within the densest parts of molecular clouds bright in the CO( = 2-1)
line emission. The two molecular clouds show a complementary spatial
distribution with a spatial displacement of 6.2 pc, and show a V-shaped
structure in the position-velocity diagram. These observational features traced
by CO and its isotopes are consistent with those in high-mass star-forming
regions created by cloud-cloud collisions in the Galactic and Magellanic Cloud
HII regions. Our new finding in M33 indicates that the cloud-cloud collision is
a promising process to trigger high-mass star formation in the Local Group.Comment: 13 pages, 10 figures, 1 table, accepted for publication in PAS
3 to 12 millimetre studies of dense gas towards the western rim of supernova remnant RX J1713.7-3946
The young X-ray and gamma-ray-bright supernova remnant RXJ1713.7-3946 (SNR
G347.3-0.5) is believed to be associated with molecular cores that lie within
regions of the most intense TeV emission. Using the Mopra telescope, four of
the densest cores were observed using high-critical density tracers such as
CS(J=1-0,J=2-1) and its isotopologue counterparts, NH3(1,1) and (2,2) inversion
transitions and N2H+(J=1-0) emission, confirming the presence of dense gas
>10^4cm^-3 in the region. The mass estimates for Core C range from 40M_{\odot}
(from CS(J=1-0)) to 80M_{\odot} (from NH3 and N2H+), an order of magnitude
smaller than published mass estimates from CO(J=1-0) observations. We also
modelled the energy-dependent diffusion of cosmic-ray protons accelerated by
RXJ1713.7-3946 into Core C, approximating the core with average density and
magnetic field values. We find that for considerably suppressed diffusion
coefficients (factors \chi=10^{-3} down to 10^{-5} the galactic average), low
energy cosmic-rays can be prevented from entering the inner core region. Such
an effect could lead to characteristic spectral behaviour in the GeV to TeV
gamma-ray and multi-keV X-ray fluxes across the core. These features may be
measurable with future gamma-ray and multi-keV telescopes offering arcminute or
better angular resolution, and can be a novel way to understand the level of
cosmic-ray acceleration in RXJ1713.7-3946 and the transport properties of
cosmic-rays in the dense molecular cores.Comment: 17 pages, 13 figures and 5 tables. Accepted for publication in MNRAS
2012 February 1
Dense Gas Towards the RX J1713.7–3946 Supernova Remnant
We present results from a Mopra 7 mm-wavelength survey that targeted the dense gas-tracing CS(1-0) transition towards the young γ-ray-bright supernova remnant, RX J1713.7–3946 (SNR G 347.3−0.5). In a hadronic γ-ray emission scenario, where cosmic ray (CR) protons interact with gas to produce the observed γ-ray emission, the mass of potential CR target material is an important factor. We summarise newly discovered dense gas components, towards Cores G and L, and Clumps N1, N2, N3, and T1, which have masses of 1 – 104 M ☉. We argue that these components are not likely to contribute significantly to γ-ray emission in a hadronic γ-ray emission scenario. This would be the case if RX J1713.7–3946 were at either the currently favoured distance of ~1 kpc or an alternate distance (as suggested in some previous studies) of ~6 kpc. This survey also targeted the shock-tracing SiO molecule. Although no SiO emission corresponding to the RX J1713.7–3946 shock was observed, vibrationally excited SiO(1-0) maser emission was discovered towards what may be an evolved star. Observations taken 1 yr apart confirmed a transient nature, since the intensity, line-width, and central velocity of SiO(J = 1-0,v = 1,2) emission varied significantly
EMU Detection of a Large and Low Surface Brightness Galactic SNR G288.8-6.3
We present the serendipitous detection of a new Galactic Supernova Remnant
(SNR), G288.8-6.3 using data from the Australian Square Kilometre Array
Pathfinder (ASKAP)-Evolutionary Map of the Universe (EMU) survey. Using
multi-frequency analysis, we confirm this object as an evolved Galactic SNR at
high Galactic latitude with low radio surface brightness and typical SNR
spectral index of . To determine the magnetic field
strength in SNR G288.8-6.3, we present the first derivation of the
equipartition formulae for SNRs with spectral indices . The
angular size is 1.\!^\circ 8\times 1.\!^\circ 6 (107.\!^\prime 6 \times
98.\!^\prime 4) and we estimate that its intrinsic size is pc which
implies a distance of kpc and a position of pc above the
Galactic plane. This is one of the largest angular size and closest Galactic
SNRs. Given its low radio surface brightness, we suggest that it is about 13000
years old.Comment: Accepted for publication in The Astrophysical Journa