Issue |
A&A
Volume 414, Number 2, February I 2004
|
|
---|---|---|
Page(s) | 475 - 486 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20031636 | |
Published online | 19 January 2004 |
Cold dust in a selected sample of nearby galaxies
I. The interacting galaxy NGC 4631
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2
SMTO, Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, Arizona 85721, USA
Corresponding author: M. Dumke, mdumke@mpifr-bonn.mpg.de
Received:
14
April
2003
Accepted:
17
October
2003
We have observed the continuum emission of the interacting galaxy
NGC 4631 at 870 μm and 1.23 mm using the
Heinrich-Hertz-Telescope on Mt. Graham and the IRAM 30-m telescope
on Pico Veleta. We have obtained fully sampled maps which cover the
optical emission out to a radius of about
at both wavelengths.
For a detailed analysis, we carefully subtracted the
line contributions and synchrotron and free-free emission from the data,
which added up to 6% at 1.23 mm and 10% at 0.87 mm.
We combined the flux densities with FIR data to obtain dust spectra and
calculate dust temperatures, absorption cross sections, and masses.
Assuming a “standard” dust model, which consists of two populations of
big grains at moderate and warm temperatures, we obtained temperatures
of 18 K and 50 K for the both components.
However, such a model suffers from an excess of the radiation at
mm, and the dust absorption cross section seems
to be enhanced by a factor 3 compared to previous results and theoretical
expectations. At large galactocentric radii, where the galaxy shows
disturbances as a result of gravitational interaction, this effect seems to
be even stronger.
Some possibilities to resolve these problems are discussed.
The data could be explained by a very cold dust component at a
temperature of 4–6 K, an increased abundance of very small grains,
or a component of grains with unusual optical properties. We favour
the latter possibility, since the first two lead to inconsistencies
Key words: galaxies: ISM / radio continuum: galaxies / galaxies: individual: NGC 4631
© ESO, 2004
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