26 research outputs found
Magneto-hydrodynamic Simulations of a Jet Drilling an HI Cloud: Shock Induced Formation of Molecular Clouds and Jet Breakup
The formation mechanism of the jet-aligned CO clouds found by NANTEN CO
observations is studied by magnetohydrodynamical (MHD) simulations taking into
account the cooling of the interstellar medium. Motivated by the association of
the CO clouds with the enhancement of HI gas density, we carried out MHD
simulations of the propagation of a supersonic jet injected into the dense HI
gas. We found that the HI gas compressed by the bow shock ahead of the jet is
cooled down by growth of the cooling instability triggered by the density
enhancement. As a result, cold dense sheath is formed around the interface
between the jet and the HI gas. The radial speed of the cold, dense gas in the
sheath is a few km/s almost independent of the jet speed. Molecular clouds can
be formed in this region. Since the dense sheath wrapping the jet reflects
waves generated in the cocoon, the jet is strongly perturbed by the vortices of
the warm gas in the cocoon, which breaks up the jet and forms a secondary shock
in the HI-cavity drilled by the jet. The particle acceleration at the shock can
be the origin of radio and X-ray filaments observed near the eastern edge of
W50 nebula surrounding the galactic jet source SS433.Comment: 30 pages, 16 figure
Discovery of possible molecular counterparts to the infrared Double Helix Nebula in the Galactic center
We have discovered two molecular features at radial velocities of -35 km/s
and 0 km/s toward the infrared Double Helix Nebula (DHN) in the Galactic center
with NANTEN2. The two features show good spatial correspondence with the DHN.
We have also found two elongated molecular ridges at these two velocities
distributed vertically to the Galactic plane over 0.8 degree. The two ridges
are linked by broad features in velocity and are likely connected physically
with each other. The ratio between the 12CO J=2-1 and J=1-0 transitions is 0.8
in the ridges which is larger than the average value 0.5 in the foreground gas,
suggesting the two ridges are in the Galactic center. An examination of the K
band extinction reveals a good coincidence with the CO 0 km/s ridge and is
consistent with a distance of 8 +/-2 kpc. We discuss the possibility that the
DHN was created by a magnetic phenomenon incorporating torsional Alfv\'en waves
launched from the circumnuclear disk (Morris, Uchida & Do 2006) and present a
first estimate of the mass and energy involved in the DHN.Comment: 32 pages, 23 figures, Accepted by Ap
Electric-field gradients in thin face-centered-tetragonal Co films observed by nuclear magnetic resonance
Evidence for a Cloud-Cloud Collision in Sh2-233 Triggering the Formation of the High-mass Protostar Object IRAS 05358+3543
We have carried out a new kinematical analysis of the molecular gas in the
Sh2-233 region by using the CO = 2-1 data taken at 0.5 pc resolution.
The molecular gas consists of a filamentary cloud of 5-pc length with 1.5-pc
width where two dense cloud cores are embedded. The filament lies between two
clouds, which have a velocity difference of 2.6 km s and are extended
over 5 pc. We frame a scenario that the two clouds are colliding with
each other and compressed the gas between them to form the filament in
0.5 Myr which is perpendicular to the collision. It is likely that the
collision formed not only the filamentary cloud but also the two dense cores.
One of the dense cores is associated with the high-mass protostellar candidate
IRAS 05358+3543, a representative high-mass protostar. In the monolithic
collapse scheme of high mass star formation, a compact dense core of 100
within a volume of 0.1 pc radius is assumed as the initial condition,
whereas the formation of such a core remained unexplained in the previous
works. We argue that the proposed collision is a step which efficiently
collects the gas of 100 into 0.1 pc radius. This lends support for
that the cloud-cloud collision is an essential process in forming the compact
high-mass dense core, IRAS 05358+3543.Comment: 12 pages, 10 figures, two tables, submitted to Monthly Notices of
Royal Astronomical Society(MNRAS