| Issue |
A&A
Volume 365, Number 3, January IV 2001
|
|
|---|---|---|
| Page(s) | 598 - 611 | |
| Section | The Sun | |
| DOI | https://doi.org/10.1051/0004-6361:20000052 | |
| Published online | 15 January 2001 | |
Infrared dark clouds from the ISOGAL survey *
Constraints on the interstellar extinction curve
1
Laboratoire de Radioastronomie Millimétrique, UMR 8540 du CNRS, École Normale Supérieure et Observatoire de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
2
Physical Research Laboratory, Navarangpura, Ahmedabad 380009, India
Corresponding author: M. Pérault, This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
28
July
2000
Accepted:
24
October
2000
Abstract
The ISO galactic survey provides images of the inner disk in two broad
filters (around 7 and 15 μm) over some 15 square degrees, away
from the brightest star forming regions.
A multiresolution analysis of the images leads to a catalogue of infrared dark
clouds, most of which are condensed cores of large molecular clouds,
several kpc away from the Sun, seen in absorption in front of the
diffuse galactic emission. The longitude distributions of the
background emission and of the dark clouds correlate with known
tracers of young population components.
We analyse the morphology of the dark clouds and the intensity
fluctuations within the cloud boundaries at the two wavelengths.
The 7 to 15 μm contrast ratio is 
for the clouds
located away from the Galactic Centre (
) and 
for the clouds closest to
the Galactic Centre (
).
Using a simple absorption model, we derive a 7 to 15 μm opacity ratio
equal to 
for the clouds located away from the Galactic Centre
and estimate the opacity, τ, of a few objects at 15 μm
in the range 1 to 4.
Several explanations for the variation of the contrast ratio,
including absorption along the line of sight and local
variations of the extinction curve are discussed.
Key words: ISM: clouds, dust, structure / Galaxy: structure / infrared: general
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA. The images have been obtained and processed by the ISOGAL collaboration.
© ESO, 2001
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