Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........10h&link_type=abstract
Thesis (PH.D.)--THE OHIO STATE UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-06, Section: B, page: 3
Computer Science
12
Virgo, Baade'S Window, Coma Cluster
Scientific paper
Red (6800-9200 A) and near-infrared (K-band) spectra have been obtained for 34 early-type galaxies in the Virgo cluster, the Coma cluster and the field. The strengths of the Ca II triplet (lambdalambda 8498, 8542, 8662 A), the Na I doublet ( lambdalambda8183, 8195 A), the Mg I lambda8807 A line, and molecular bands of TiO and VO were measured from the red spectra. Absorption due to the CO band with bandhead at 2.29 mu m was measured from the near-infrared spectra. The behavior of the spectral indices was examined for the Virgo galaxy nuclei as functions of luminosity and color. Overall, the CO, TiO and Na I indices were found to be stronger in redder and brighter galaxies. The Mg I and the Ca II triplet lines did not vary significantly among galaxies of different color or brightness. These trends are consistent with a change in chemical composition producing the well-known color-magnitude relation for early -type galaxies. No significant differences were detected among galaxies of similar luminosity in the Virgo cluster, the Coma cluster and the field. To simulate the stellar population changes implied by the radial color gradients observed in early-type galaxies, models were constructed to represent the integrated light of the Galactic bulge as a function of latitude. A field in Baade's Window (BW) was studied first and the stellar population there was found to be quite inhomogeneous. The BW model indicated that the integrated light of BW is giant -dominated, and the BW spectral energy distribution is very similar to that of the nucleus of a low-luminosity early -type galaxy. From models of BW and a field at b = -8^circ, radial gradients were estimated for the Galactic bulge and compared to the changes which occur along a luminosity sequence of early -type galaxies in the Virgo cluster. This comparison showed that: (1) the Na I and I(8197) indices increase steeply with redder colors in the Virgo galaxies but appear to decrease with color in the Galactic bulge; this effect is not understood but may be caused by some deficiency in the modelling; and (2) differences in the slopes of the TiO-color trends in E/S0 galaxies and in the Galactic bulge may indicate that the (Ti/Fe) ratio is changing differently in these two instances.
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