EDP Sciences
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Volume 391, Number 2, August IV 2002
Page(s) 429 - 440
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020879

A&A 391, 429-440 (2002)
DOI: 10.1051/0004-6361:20020879

Mid-infrared observations of the ultraluminous galaxies IRAS 14348-1447 , IRAS 19254-7245 , and IRAS 23128-5919

V. Charmandaris1, O. Laurent2, 3, E. Le Floc'h2, I. F. Mirabel2, 4, M. Sauvage2, S. C. Madden2, P. Gallais2, L. Vigroux2 and C. J. Cesarsky5

1  Cornell University, Astronomy Department, Ithaca, NY 14853, USA
2  CEA/DSM/DAPNIA Service d'Astrophysique, 91191 Gif-sur-Yvette, France
3  Max Planck Institut für extraterrestrische Physik, PO Box 1312, 85740 Garching, Germany
4  Instituto de Astronomía y Física del Espacio, Conicet, cc 67, suc 28. 1428 Buenos Aires, Argentina
5  European Southern Observatory, Karl-Schwarzschild-Str, 85748 Garching bei München, Germany

(Received 1 March 2002 / Accepted 30 May 2002)

We present a study of the three ultraluminous infrared galaxies IRAS 14348-1447, IRAS 19254-7245, and IRAS 23128-5919, based on mid-infrared (MIR) spectro-imaging (5-18 $\mu$m) observations performed with ISOCAM. We find that the MIR emission from each system, which consists of a pair of interacting late type galaxies, is principally confined to the nuclear regions with diameters of 1-2 kpc and can account for more than 95% of their IRAS 12 $\mu$m flux. In each interacting system, the galaxy hosting an active galactic nucleus (AGN) dominates the total spectrum and shows stronger dust continuum (12-16 $\mu$m) relative to the Unidentified Infrared Band (UIB) emission (6-9 $\mu$m), suggestive of its enhanced radiation field. The MIR dominant galaxy also exhibits elevated 15 $\mu$m/H $\alpha$ and 15 $\mu$m/K ratios which trace the high extinction due to the large quantities of molecular gas and dust present in its central regions. Using only diagnostics based on our mid-infrared spectra, we can establish that the Seyfert galaxy IRAS 19254-7245 exhibits MIR spectral features of an AGN while the MIR spectrum of the Seyfert (or LINER) member of IRAS 23128-5919 is characteristic of dust emission principally heated by star forming regions.

Key words: galaxies: active -- galaxies: individual: IRAS 14348-1447 -- galaxies: individual: IRAS 19254-7245 -- galaxies: individual: IRAS 23128-5919 -- galaxies: interactions -- infrared: galaxies

Offprint request: V. Charmandaris, vassilis@astro.cornell.edu

© ESO 2002