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Far-Infrared Emission From E and E/S0 Galaxies
Studies of cold material through IRAS 60um and 100um observations indicated
that half of ordinary E and E/S0 galaxies were detected above the 3 sigma
level, indicating that cold gas is common, although no correlation was found
between the optical and far- infrared fluxes. Most detections were near the
instrumental threshold, and given an improved understanding of detection
confidence, we reconsider the 60um and 100um detection rate. After excluding
active galactic nuclei, peculiar systems, and background contamination, only 15
non-peculiar E and E/S0 galaxies from the RSA catalog are detected above the
98% confidence level, about 12% of the sample. An unusually high percentage of
these 15 galaxies possess cold gas (HI, CO) and optical emission lines
(Halpha), supporting the presence of gas cooler than 10E4 K. The 60um to 100um
flux ratios imply a median dust temperature for the sample of 30 K, with a
range of 23-38 K.
These detections define the upper envelope of the optical to far-infrared
relationship, F_fir propto F_B^0.24+/-0.08, showing that optically bright
objects are also brighter in the infrared, although with considerable
dispersion. A luminosity correlation is present with L_fir propto
L_B^1.65+/-0.28, but the dust temperature is uncorrelated with luminosity.
Models that contain large dust grains composed of amorphous carbon plus
silicates come close to reproducing the typical 60um to 100um flux ratios, the
far-infrared luminosity, and the L_fir - L_B relationship.Comment: 10 postscript pages, 2 tables, and 2 figure