105 research outputs found
Vigorous star formation hidden by dust in a galaxy at
Near-infrared surveys have revealed a substantial population of enigmatic
faint galaxies with extremely red optical-to-near-infrared colours and with a
sky surface density comparable to that of faint quasars. There are two
scenarios for these extreme colours: (i) these distant galaxies have formed
virtually all their stars at very high redshifts and, due to the absence of
recently formed stars, the colours are extremely red and (ii) these distant
galaxies contain large amounts of dust, severely reddening the rest-frame
UV--optical spectrum. HR10 () is considered the archetype of the
extremely red galaxies. Here we report the detection of the continuum emission
from HR10 at 850m and at 1250m, demonstrating that HR10 is a very
dusty galaxy undergoing a major episode of star formation. Our result provides
a clear example of a high-redshift galaxy where the star formation rate
inferred from the ultraviolet luminosity would be underestimated by a factor up
to 1000, and shows that great caution should be used to infer the global star
formation history of the Universe from optical observations only.Comment: 12 pages, 1 figure, Nature, in press (30 April 1998
The Role of Grains in Molecular Chemical Evolution
Wetensch. publicati
Interstellar Dust Close to the Sun
The low density interstellar medium (ISM) close to the Sun and inside of the
heliosphere provides a unique laboratory for studying interstellar dust grains.
Grain characteristics in the nearby ISM are obtained from observations of
interstellar gas and dust inside of the heliosphere and the interstellar gas
towards nearby stars. Comparison between the gas composition and solar
abundances suggests that grains are dominated by olivines and possibly some
form of iron oxide. Measurements of the interstellar Ne/O ratio by the
Interstellar Boundary Explorer spacecraft indicate that a high fraction of
interstellar oxygen in the ISM must be depleted onto dust grains. Local
interstellar abundances are consistent with grain destruction in ~150 km/s
interstellar shocks, provided that the carbonaceous component is hydrogenated
amorphous carbon and carbon abundances are correct. Variations in relative
abundances of refractories in gas suggest variations in the history of grain
destruction in nearby ISM. The large observed grains, > 1 micron, may indicate
a nearby reservoir of denser ISM. Theoretical three-dimensional models of the
interaction between interstellar dust grains and the solar wind predict that
plumes of about 0.18 micron dust grains form around the heliosphere.Comment: 2011 AGOS Taiwan meeting; accepted for publication in Earth, Planets
and Spac
A supernova origin for dust in a high-redshift quasar
Interstellar dust plays a crucial role in the evolution of the Universe by
assisting the formation of molecules, by triggering the formation of the first
low-mass stars, and by absorbing stellar ultraviolet-optical light and
subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought
to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass
stars. This picture has, however, recently been brought into question by the
discovery of large masses of dust in the host galaxies of quasars at redshift
z>6, when the age of the Universe was less than 1 Gyr. Theoretical studies,
corroborated by observations of nearby supernova remnants, have suggested that
supernovae provide a fast and efficient dust formation environment in the early
Universe. Here we report infrared observations of a quasar at redshift 6.2,
which are used to obtain directly its dust extinction curve. We then show that
such a curve is in excellent agreement with supernova dust models. This result
demonstrates a supernova origin for dust in this high-redshift quasar, from
which we infer that most of the dust at high redshifts has probably the same
origin.Comment: To Appear in Nature, September 30, 200
Interstellar Grains: Effect of Inclusions on Extinction
A composite dust grain model which simultaneously explains the observed
interstellar extinction, polarization, IR emission and the abundance
constraints, is required. We present a composite grain model, which is made up
of a host silicate oblate spheroid and graphite inclusions. The interstellar
extinction curve is evaluated in the spectral region 3.4-0.1 using the
extinction efficiencies of the composite spheroidal grains for three axial
ratios. Extinction curves are computed using the discrete dipole approximation
(DDA). The model curves are subsequently compared with the average observed
interstellar extinction curve and with an extinction curve derived from the IUE
catalogue data.Comment: 10 pages, 3 figure
Grain Alignment in Molecular Clouds
One of the most informative techniques of studying magnetic fields in
molecular clouds is based on the use of starlight polarization and polarized
emission arising from aligned dust. How reliable the interpretation of the
polarization maps in terms of magnetic fields is the issue that the grain
alignment theory addresses.
I briefly review basic physical processes involved in grain alignment.Comment: 8 papes, 1 figures, to appear in Zermatt proceeding
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