Physics
Scientific paper
Feb 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sgyu.conf...55y&link_type=abstract
Studies of Galaxies in the Young Universe with New Generation Telescope, Proceedings of Japan-German Seminar, held in Sendai, Ja
Physics
1
Scientific paper
The age of elliptical galaxies is very important to reveal their formation. However it has not been determined for a long time because there is age-metallicity degeneracy in galaxy spectra. Old indices for hydrogen Balmer lines (Worthey et al. 1994, Jones & Worthey 1995, Worthey & Ottaviani 1997) cannot measure age without information of metallicity. We use the new index Hγσ (Vazdekis & Arimoto 1999) to determine age of elliptical galaxies. The wavelength definition of this index is appropriate for determination of accurate age taking account of many metallic lines around Hγ and spectral convolution because of velocity dispersion of stars in galaxy. In this study, ages of 15 ellipticals (8 nearby field ellipticals and 7 Virgo cluster ellipticals) are determined by measuring Hγσ index with my SSP model. There is no clear trends between the age and the velocity dispersion σ for these galaxies, they have almost constant old ages (≥ 10 Gyr), though the average age of Virgo ellipticals are slightly larger than that of field ellipticals. Their metallicities are also measured by using metallic lines (Mgb, Fe4383), [Mg/Fe] values of smaller galaxies both in field and in cluster are smaller than that of greater galaxies. These results indicate that the main origin of CM relation is metallicity. However more clear age-σ relation can be seen if dwarf (faint) galaxies are included. i.e. smaller galaxies have younger age than larger. Neither ¡Èmonolithic collapse" nor "hierarchical clustering" can explain the age-σ and the [Mg/Fe]-σ relation for these elliptical galaxies.
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