Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-06-23
Astronomy and Astrophysics
Astrophysics
To appear in the Astrophysical Journal. Figure 1 appears as a separate jpg figure
Scientific paper
10.1086/317119
Four IRAS-detected early type galaxies were observed with ISO. With the exception of the 15 micron image of NGC1052, the mid-IR emission from NGC1052, NGC1155, NGC5866 and NGC6958 at 4.5, 7 and 15 microns show extended emission. Mid-IR emission from NGC1052, NGC1155, and NGC6958 follows a de Vaucouleurs profile. The ratio of 15/7 micron flux decreases with radius in these galaxies, approaching the values empirically observed for purely stellar systems. In NGC5866, the 7 and 15 micron emission is concentrated in the edge-on dust lane. All the galaxies are detected in the [CII] line, and the S0s NGC1155 and NGC5866 are detected in the [OI] line as well. The ISO-LWS observations of the [CII] line are more sensitive measures of cool, neutral ISM than HI and CO by about a factor of 10-100. Three of four early type galaxies, namely NGC1052, NGC6958 and NGC5866, have low ratio FIR/Blue and show a lower [CII]/FIR, which is due to a softer radiation field from old stellar populations. The low [CII]/CO ratio in NGC5866 ([CII]/CO(1-0) < 570) confirms this scenario. We estimate the UV radiation expected from the old stellar populations in these galaxies and compare it to that needed to heat the gas to account for the cooling observed [CII] and [OI] lines. In three out of four galaxies, NGC1052, NGC5866 and NGC6958, the predicted UV radiation falls short by a factor of 2-3. In view of the observed intrinsic scatter in the "UV-upturn" in elliptical galaxies and its great sensitivity to age and metallicity effects, this is not significant. However, the much larger difference (about a factor of 20) between the UV radiation from old stars and that needed to produce the FIR lines for NGC 1155 is strong evidence for the presence of young stars, in NGC1155.
Dale Daniel
Dinerstein Harriet
Helou George
Hollenbach David
Hunter Deidre
No associations
LandOfFree
Probing the Interstellar Medium in Early type galaxies with ISO observations does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Probing the Interstellar Medium in Early type galaxies with ISO observations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Probing the Interstellar Medium in Early type galaxies with ISO observations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-95538