Disentangling the Effects of Dust, Age, and Metallicity in Stellar Populations
Session 77 -- Spirals II
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

## [77.01] Disentangling the Effects of Dust, Age, and Metallicity in Stellar Populations

Roger Rouse (Arizona State University)

\def\aaccent{${\rm\acute{a}}$} \parindent 0pt One of the most confounding conspiracies in nature is the fact that differences in dust content, in metallicity, and/or in age have similar effects on the integrated light of a stellar population. The data available for separating these effects consist of observations of 10 spiral galaxies with longslit optical spectra and BVRIJHK imaging. The spectra were taken at the MMT with the Red Channel spectrograph in collaboration with D. Burstein. The optical imaging was done at the MDM 1.5m courtesy, G. Wegner. The IR imaging was done at the Steward Observatory's 61$''$ in collaboration with M. Reike. In each galaxy the longslit is placed over two bright points in the galaxy, with one taken as the galaxy center so that the slit falls along a radius. The galaxies are of moderate size ($\approx 3'$), permitting the slit to sample stellar populations in both the bulge and disks of these galaxies. Spectra were obtained at each of two slit positions and at each of two dispersions.

The position and width of the slit (2$''$) are superimposed on the optical and infrared images, permitting one to form optical-infrared colors at points along the slit corresponding to the extracted spectra. From the spectra line indices have been measured on the Lick system, which permit easy comparison to the existing models of Worthey (Ph.D. 1992, UC Santa Cruz) and similar data on elliptical galaxies (Gonz\aaccent lez 1993, UC Santa Cruz). The principle age/metallicity discriminant in the Lick system as found by Worthey and Gonz\aaccent lez, $\rm H\beta$ vs. $\rm \log (MgFe)$, is used to separate age and metallicity effects in the stellar populations. Reddening is separated from stellar population differences by combining colors and line strengths. For this poster, this analysis will be applied in full to one of the galaxies, NGC 4654; the completed Ph.D. thesis will contain similar analyses for all 10 galaxies.