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Astron. Astrophys. 341, 69-73 (1999)

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Dust in the wheel: The Cartwheel galaxy in the Mid-IR *

V. Charmandaris 1,2, O. Laurent 2, I.F. Mirabel 2, P. Gallais 2, M. Sauvage 2, L. Vigroux 2, C. Cesarsky 2 and P.N. Appleton 3

1 Observatoire de Paris, DEMIRM, 61 Av. de l'Observatoire, F-75014 Paris, France
2 Service d'Astrophysique, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex, France
3 Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA

Received 9 July 1998 / Accepted 13 October 1998


We present mid-infrared images at [FORMULA] and [FORMULA] of "The Cartwheel" (AM 0035-33), the prototypical collisional ring galaxy. The observations, taken with ISOCAM, reveal the distribution of hot dust in the galaxy and its two companions in the north-east. The intensity of the Mid-IR emission from the outer star forming ring of the Cartwheel shows considerable azimuthal variation and peaks at the most active H[FORMULA] region of the ring. The 15 [FORMULA] to 6.7 [FORMULA] flux ratio of 5.2 is the highest among all the galaxies of our sample. A surprising result of our observations is the discovery of significant emission from the inner regions of the galaxy, including the inner ring, spokes and nucleus, where previously only low level H[FORMULA] emission had been reported. At 6.7 [FORMULA], this emission is stronger than the one from the outer star forming ring, and at 15 [FORMULA], it represents 40% of the emission from the outer ring. The H[FORMULA] to Mid-IR flux ratios from the inner regions are consistent with the heating of grains from weak star formation activity.

Key words: infrared: ISM: continuum – galaxies: starbust – galaxies: interactions – galaxies: individual: The Cartwheel – stars: formation

* 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 United Kingdom) with the participation of ISAS and NASA.

Send offprint requests to: V. Charmandaris (v.charmandaris@obspm.fr)

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© European Southern Observatory (ESO) 1999

Online publication: November 26, 1998