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Session 67 - ISM in Galaxies.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[67.02] Mid-Infrared Spectroscopy of Normal Galaxies

N. Y. Lu, G. Helou, C. A. Beichman (IPAC/Caltech), H. L. Dinerstein (U. Texas), D. J. Hollenbach, R. H. Rubin (NASA/Ames), D. A. Hunter (Lowell Obs.), K. Y. Lo (U. Illinois), S. Lord, S. Malhotra, N. Silbermann (IPAC/Caltech), G. Stacey (Cornell U.), H. Thronson (U. Wyoming), M. W. Werner (JPL)

We are using the PHT-S spectrometer on board the Infrared Space Observatory (ISO) to obtain mid-infrared spectra from 2.5 to 5\,\mum and from 6 to 12\,\mum on a broad sample of about 50 star-forming galaxies. The spectra we have obtained so far show prominent emission features centered at 6.2, 7.7, 8.6 and 11.3\,\mum, presumably from the so-called Polycyclic Aromatic Hydrocarbons (PAH) molecules. But the PAH feature at 3.3\,\mum, which have been detected in Galactic sources and some external galaxies, are generally not detected in our galaxies. Except in a few cases, the relative strengths among the detected PAH features vary moderately from galaxy to galaxy. We will show the PHT-S spectra; characterize the variation of PAH relative strengths and its correlation with other galaxy properties including the mid-infrared color data from ISO-CAM images; and report the tentative detection of a continuum in the 3-to-5\,\muu range, whose origin remains unclear.

ISO (the Infrared Space Observatory) is an ESA mission with participation by NASA and ESA. The PHT (ISO Photometer) was built by Lemke et al (1996, Aamp;A Letters, Nov. 10 issue).

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Program listing for Wednesday