The Radial Variation of Color and Line Indices in NGC~4654 and NGC~3338: Mixed-Aged Stellar Populations
Session 109 -- Stellar Populations
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [109.02] The Radial Variation of Color and Line Indices in NGC~4654 and NGC~3338: Mixed-Aged Stellar Populations

Roger Rouse (Arizona State University)

\parindent 0pt \def\Dnsig{\ ${\rm D_n-\sigma}$\ } \def\B-H{\ ${\rm B_{T}-H_{-0.5}}$\ } \def\2by180{\ $\rm 2'' \times 180''$\ } The galaxies NGC~4654 and NGC~3338 are part of a sample of 10 spiral galaxies paired in \B-H color. The ten have been observed with the MMT Red Channel Spectrograph (with D. Burstein, A.S.U.), the NICMOS 256x256 IR array at the Catalina Observatory's 61$''$ (with M. Reike, U. of A.) and the MDM RCA CCD at the McGraw Hill Observatory (with G. Wegner, Dartmouth). The spectra were taken using a \2by180 slit at two position angles at both 3.2${\rm \AA/pixel}$ and 1.6${\rm \AA/pixel}$. The IR imaging was done in JHK and the optical imaging in BVRI (1992, BAAS 24, 1183). Presented here are line indices on the Lick system, optical-IR colors, and surface brightness profiles. Along with radial variations, any observed correlations between line indices and colors will be discussed, as well as differential radial variations in stellar populations. The accuracy to which line strengths from spectra can be matched to galaxy colors from direct images will be quantitatively assessed. These data are on the Lick system of color and line indices and can be directly compared to the synthetic stellar population models of G. Worthey (1992,Ph.D. thesis), which span a wide range of age and metallicity, as well as to analogous existing observations of elliptical galaxies. The data from the {\it whole} sample of 10 galaxies are being used to determine what kinds of stellar populations exist in the disks of spiral galaxies and will form a library of spectra and colors for stellar populations known to consist of subpopulations of various ages, 0.5-4 Gyr. This study should reveal the degree to which integrated colors of spiral galaxies, such as \B-H, are correlated with age or metallicity in these mixed-aged stellar populations. Other questions this thesis can address are: How do the stellar populations of disks compare to those of recent mergers? Will the data give insight to the physical cause of the Tully-Fisher relation? Is there a correlation between stellar populations in the disks of spirals and the environments of the host galaxies? Is it possible to use this library as a local standard for comparison to spiral galaxies of non-negligible redshift?
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