268 research outputs found
A low-mass HI companion of NGC 1569?
High-sensitivity maps of the large-scale structure of atomic hydrogen in the
starburst dwarf galaxy NGC 1569 show evidence for an HI cloud with a mass of
7*10**6 M_sun, at a projected distance of 5 kpc from the parent galaxy. This
cloud may be a condensation in a low-column-density HI halo or a companion
galaxy/HI-cloud. NGC 1569 and its companion are connected by a low surface
brightness HI bridge. At the edge of NGC1569, the HI bridge coincides with
H_alpha arcs, also detected in soft X-rays.Comment: 5 pages, 4 figures, 1 tabl
SCUBA Observations of NGC 1275
Deep SCUBA observations of NGC 1275 at 450 micron and 850 micron along with
the application of deconvolution algorithms have permitted us to separate the
strong core emission in this galaxy from the fainter extended emission around
it. The core has a steep spectral index and is likely due primarily to the AGN.
The faint emission has a positive spectral index and is clearly due to extended
dust in a patchy distribution out to a radius of 20 kpc from the
nucleus. These observations have now revealed that a large quantity of dust,
6 10 , 2 orders of magnitude larger than that
inferred from previous optical absorption measurements, exists in this galaxy.
We estimate the temperature of this dust to be 20 K (using an emissivity
index of = 1.3) and the gas/dust ratio to be 360. These values are
typical of spiral galaxies. The dust emission correlates spatially with the hot
X-ray emitting gas which may be due to collisional heating of broadly
distributed dust by electrons. Since the destruction timescale is short, the
dust cannot be replenished by stellar mass loss and must be externally
supplied, either via the infalling galaxy or the cooling flow itself.Comment: 13 pages, 4 figures. Figure 4 is colou
The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?
We discuss the interpretation of the dust SED from the mid-infrared to the
millimeter range of NGC 1569. The model developed by D\'esert et al. (1990)
including three dust components (Polyaromatic Hydrocarbons, Very Small Grains
and big grains) can explain the data using a realistic interstellar radiation
field and adopting an enhanced abundance of VSGs. A simple three-temperature
model is also able to reproduce the data but requires a very low dust
temperature which is considered to be unlikely in this low-metallicity
starburst galaxy. The high abundance of Very Small Grains might be due to large
grain destruction in supernova shocks. This possibility is supported by ISO
data showing that the emission at 14.3 m, tracing VSGs, is enhanced with
respect to the emission at 6.7 m and 850 m in regions of high star
formation.Comment: 4 pages, conference proceedings paper, "The Spectral Energy
Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg,
4-8 Oct. 2004, eds. C.C. Popescu & R.J. Tuffs, AIP Conf. Ser., in pres
Triggered/sequential star formation? A multi-phase ISM study around the prominent IRDC G18.93-0.03
G18.93-0.03 is a prominent dust complex within an 0.8deg long filament, with
the molecular clump G18.93/m being IR dark from near IR wavelength up to 160mu.
Spitzer composite images show an IR bubble spatially associated with G18.93. We
use GRS 13CO and IRAM 30m H13CO+ data to disentangle the spatial structure of
the region. From ATLASGAL submm data we calculate the gas mass, while we use
the H13CO+ line width to estimate its virial mass. Using HERSCHEL data we
produce temperature maps from fitting the SED. With the MAGPIS 20cm and
SuperCOSMOS Halpha data we trace the ionized gas, and the VGPS HI survey
provides information on the atomic hydrogen gas. We show that the bubble is
spatially associated with G18.93, located at a kinematic near distance of
3.6kpc. With 280Msun, the most massive clump within G18.93 is G18.93/m. The
virial analysis shows that it may be gravitationally bound and has neither
Spitzer young stellar objects nor mid-IR point sources within. Fitting the SED
reveals a temperature distribution that decreases towards its center, but
heating from the ionizing source puts it above the general ISM temperature. We
find that the bubble is filled by HII gas, ionized by an O8.5 star. Between the
ionizing source and the IR dark clump G18.93/m we find a layered structure,
from ionized to atomic to molecular hydrogen, revealing a PDR. Furthermore, we
identify an additional velocity component within the bubble's 8mu emission rim
at the edge of the infrared dark cloud and speculate that it might be shock
induced by the expanding HII region. While the elevated temperature allows for
the build-up of larger fragments, and the shock induced velocity component may
lead to additional turbulent support, we do not find conclusive evidence that
the massive clump G18.93/m is prone to collapse because of the expanding HII
region.Comment: Accepted for publication in A&
- …