Other
Scientific paper
Mar 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..813m&link_type=abstract
The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 813
Other
2
Elliptical Galaxies, Mid-Ir, Far-Ir Spectroscopy, Ism
Scientific paper
Three IRAS-detected elliptical galaxies were observed with ISO-LWS and PHT, and two of them were observed with CAM. The mid-IR images of NGC 1155 and NGC 6958 at 7 and 15 μ m show extended emission which follows a de Vaucouleurs profile. The ratio of 15/7 μ m flux decreases with radius in both galaxies, approaching the values empirically observed for purely stellar systems. All three galaxies are detected in the [CII](158 μ m) line, and NGC 1155 in the [OI] (63 μ m) line. The ISO-LWS observations of the [CII] line are more sensitive measures of cool ISM than HI and CO; the only previous detection of cool gas was of HI in NGC 1052/LFIR ratio in ellipticals follows the same trends seen in other (spiral and irregular) galaxies wherein L[CII]/LFIR decreases with increasing Fν(60 μ m)/Fν(100 μ m). These trends indicate similar local physical conditions in the ISM in spirals and ellipticals. The UV radiation from old stellar populations is insufficient, by a factor of 2-30, to produce enough photoelectric heating of gas to account for the cooling via the [CII] and [OI] lines. Heating by X-rays is also insufficient in NGC 6958 and NGC 1155. Given the observed variations in the optical-UV colors and the uncertainties in modelling the UV from old stellar populations, we can make a clear case for young stellar populations in NGC 1155.
Dale Daniel
Dinerstein Harriet
Helou George
Hollenbach David
Hunter Deidre Ann
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