5,008 research outputs found
High Latitude HI in NGC 2613: Buoyant Disk-Halo Outflow
We combine new VLA D array HI data of NGC 2613 with previous high resolution
data to show new disk-halo features in this galaxy. The global HI distribution
is modeled in detail using a technique which can disentangle the effects of
inclination from scale height and can also solve for the average volume density
distribution in and perpendicular to the disk. The model shows that the
galaxy's inclination is on the low end of the range given by Chaves & Irwin
(2001) and that the HI disk is thin (z_e = 188 pc), showing no evidence for
halo. Numerous discrete disk-halo features are observed, however, achieving z
heights up to 28 kpc from mid-plane. One prominent feature in particular, of
mass, 8X10^7 Msun and height, 22 kpc, is seen on the advancing side of the
galaxy at a projected galactocentric radius of 15.5 kpc. If this feature
achieves such high latitudes because of events in the disk alone, then input
energies of order ~ 10^{56} ergs are required. We have instead investigated the
feasibility of such a large feature being produced via buoyancy (with drag)
within a hot, pre-existing X-ray corona. Reasonable plume densities,
temperatures, stall height (~ 11 kpc), outflow velocities and ages can indeed
be achieved in this way. The advantage of this scenario is that the input
energy need only be sufficient to produce blow-out, a condition which requires
a reduction of three orders of magnitude in energy. If this is correct, there
should be an observable X-ray halo around NGC 2613.Comment: 32 pages 7 gif figures, accepted by Ap
New unidentified H.E.S.S. Galactic sources
H.E.S.S. is one of the most sensitive instruments in the very high energy
(VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the
Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004,
H.E.S.S. has continued and extended that survey in 2005-2008, discovering a
number of new sources, many of which are unidentified. Some of the unidentified
H.E.S.S. sources have several positional counterparts and hence several
different possible scenarios for the origin of the VHE gamma-ray emission;
their identification remains unclear. Others have so far no counterparts at any
other wavelength. Particularly, the lack of an X-ray counterpart puts serious
constraints on emission models. Several newly discovered and still unidentified
VHE sources are reported here.Comment: ICRC 2009 proceeding
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