Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990nascp3084..120w&link_type=abstract
In NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers p 120-122 (SEE N91-
Astronomy and Astrophysics
Astronomy
Cosmic Dust, Elliptical Galaxies, Far Infrared Radiation, Infrared Astronomy Satellite, Infrared Radiation, Luminosity, Neutral Gases, Nonthermal Radiation, Radiation Distribution, Color, Distortion, Estimating, Flux Density, Hydrogen, Isophotes, Ratios, Sensitivity, Signatures, Spectra
Scientific paper
The incidence of dust lanes in elliptical galaxies has been estimated at approx. 40 percent by Sadler and Gerhard (1985), although the observed fraction is lower because of inclination effects. A similar percentage of ellipticals has been detected by the Infrared Astronomy Satellite (IRAS) at 100 microns (Knapp et al. 1989); these have far-infrared colors expected for emission from cool dust (S60 micron/S100 micron approx. 1/3). For the far-infrared detected galaxies, neither L100 microns/LB nor L60 microns/L100 microns are very dependent on dust content, suggesting that the source of the infrared luminosity is the same in both cases; and hence that dust is responsible even when not detected optically. Despite this indication, L100 microns does not prove to be a good indicator of the quantity of cool interstellar matter in elliptical galaxies, as measured by the mass of neutral hydrogen. There even exist several examples of ellipticals with dust, strong 100 micron flux density and sensitive limits on HI mass (Walsh et al. in preparation). Chief reasons for the lack of correlation include the existence of other important sources of far-IR power in ellipticals, such as nonthermal continuum emission extending from longer wavelengths in flat spectrum radio sources (Golombek, Miley and Neugebauer 1988); and the fact that far-infrared luminosity per unit dust mass is extremely sensitive to the temperature of the ambient radiation field, which is not accurately known. In addition to having their appearance distorted by dust, several ellipticals also show such features as shells, box-shaped isophotes or inner disks. These may be signatures of past mergers, which could also add to the ISM content of the system.
Knapp Jill
Walsh Duncan
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