572 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
Star formation history and environment of the dwarf galaxy UGCA 92
We present a quantitative star formation history of the nearby dwarf galaxy
UGCA 92. This irregular dwarf is situated in the vicinity of the Local Group of
galaxies in a zone of strong Galactic extinction (IC 342 group of galaxies).
The galaxy was resolved into stars with HST/ACS including old red giant branch.
We have constructed a model of the resolved stellar populations and measured
the star formation rate and metallicity as function of time. The main star
formation activity period occurred about 8 - 14 Gyr ago. These stars are mostly
metal-poor, with a mean metallicity [Fe/H] ~ -1.5 -- -2.0 dex. About 84 per
cent of the total stellar mass was formed during this event. There are also
indications of recent star formation starting about 1.5 Gyr ago and continuing
to the present. The star formation in this event shows moderate enhancement
from ~ 200 Myr to 300 Myr ago. It is very likely that the ongoing star
formation period has higher metallicity of about -0.6 -- -0.3 dex. UGCA 92 is
often considered to be the companion to the starburst galaxy NGC 1569.
Comparing our star formation history of UGCA 92 with that of NGC 1569 reveals
no causal or temporal connection between recent star formation events in these
two galaxies. We suggest that the starburst phenomenon in NGC 1569 is not
related to the galaxy's closest dwarf neighbours and does not affect their star
formation history.Comment: 11 pages, 9 figures, accepted to MNRA
A Molecular Spiral Arm in the Far Outer Galaxy
We have identified a spiral arm lying beyond the Outer Arm in the first
Galactic quadrant ~15 kpc from the Galactic center. After tracing the arm in
existing 21 cm surveys, we searched for molecular gas using the CfA 1.2 meter
telescope and detected CO at 10 of 220 positions. The detections are
distributed along the arm from l = 13 deg, v = -21 km/s to l = 55 deg, v = -84
km/s and coincide with most of the main H I concentrations. One of the
detections was fully mapped to reveal a large molecular cloud with a radius of
47 pc and a molecular mass of ~50,000 Mo. At a mean distance of 21 kpc, the
molecular gas in this arm is the most distant yet detected in the Milky Way.
The new arm appears to be the continuation of the Scutum-Centaurus Arm in the
outer Galaxy, as a symmetric counterpart of the nearby Perseus Arm.Comment: 11 pages, 4 figures, 1 Table, ApJ Letters, in pres
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