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Session 67 - ISM in Galaxies.
Display session, Wednesday, January 15
Half of ordinary E and E/S0 galaxies have been claimed as weak detections from IRAS observations at 60\mum and 100\mum, indicating that cold gas is common, although no correlation was found between the optical and far infrared fluxes. We reconsider this issue and after excluding AGNs, peculiar systems, and background contamination, only 15 RSA E and E/S0 galaxies are detected above the 98% confidence level, about 10% of the sample. An unusually high percentage of these 15 galaxies possess cold gas (HI, CO) and optical emission lines (H\alpha), supporting the presence of gas cooler than 10^4 K; the dust temperature lies in the range 23--38 K. We find a correlation between the far IR and B fluxes (and between their luminosities), indicating that opically bright objects are also brighter in the far infrared, although with considerable dispersion. The dust masses inferred from the far IR are an order of magnitude greater than those from extinction observations, except for the recent merger candidate NGC 4125, where they are equal. Most of the results are consistent with a model where the dust comes from stellar mass loss and the heating is by stellar photons, provided that there are large dust grains composed of amorphous carbon plus silicates.
Program listing for Wednesday