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Astron. Astrophys. 333, L1-L4 (1998)

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Letter to the Editor

The dark side of star formation in the Antennae galaxies

I.F. , Mirabel 1, L. , Vigroux 1, V. , Charmandaris 1, M. , Sauvage 1, P. , Gallais 1, D. , Tran 1, C. , Cesarsky 1, S.C. , Madden 1, P.-A. and Duc 2

1 CEA/DSM/DAPNIA Service d'Astrophysique F-91191 Gif-sur-Yvette, France
2 ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany

Received 18 December 1997 / Accepted 3 February 1998


We compare mid-infrared images of the Antennae galaxies (NGC 4038/39) from the Infrared Space Observatory, with optical images from the Hubble Space Telescope. The mid-infrared observations show that the most intense starburst in this colliding system of galaxies takes place in an off-nucleus region that is inconspicuous at optical wavelengths. The analyses of the mid-infrared spectra indicate that the most massive stars are being formed in an optically obscured knot of 50 pc radius, which produces about 15% of the total luminosity from the Antennae galaxies between 12.5 µm and 18 µm. The mid-infrared observations reported here demonstrate that the interpretation of star formation properties in colliding/merging systems based on visible wavelengths alone can be profoundly biased due to dust obscuration. The multiwavelength view of this nearby prototype merging system suggests caution in deriving scenarios of early evolution of high redshift galaxies using only observations in the narrow rest-frame ultraviolet wavelength range.

Key words: galaxies: individual: NGC 4038/39 – galaxies: individual: Antennae galaxies – infrared: interstellar: continuum – stars: formation

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© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998