Spiral Galaxy Mass Models and the Distance Scale

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Session 79 -- Structure of Galaxies
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[79.01] Spiral Galaxy Mass Models and the Distance Scale

P.Palunas, T.B.Williams (Rutgers University)

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We present mass models for a sample of Freeman Type I spiral galaxies taken from the southern sky Fabry-Perot Tully-Fisher survey(Schommer \etal 1993, Bothun \etal 1992). We fit two component, bulge and disk, photometric models directly to $I$- and $R$-band images. The bulge model is a series expansion of Gaussians (a Gabor expansion): each Gaussian in the series has a common center, ellipticity and position angle. The position angle is fixed to be the same as that of the disk. We have found that a deVaucouleurs law does not give a good fit to the bulges of many disk galaxies. The disk model is an exponential with the same center as the bulge. Small-scale radial structure is included in the disk mass model by azimuthally averaging the residuals of the analytic fit in annuli with the same ellipticity and position angle of the disk. Fitting to the full 2-d images helps constrain the disk-bulge deconvolution by using the information in the different ellipticities well as the different radial profiles of the disk and bulge. The photometric model is fitted to the rotation curve assuming a maximum disk and constant mass-to-light ratios for disk and bulge components. The small scale structure in the photometric models is found to reproduce the structure in the rotation curve in many galaxies. We find approximately 15 percent rms scatter in the $I$-band mass-to-light ratios, as well as correlations to the detailed properties of the kinematics indicating that mass-to-light ratios may be useful in reducing the scatter in the Tully-Fisher relation.

\vskip .5truecm \refp{Bothun, G.D., Schommer, R.A., Williams, T.B., Mould J.R., Huchra, J.P.,1992}{Ap. J.}{388}{253} \refp{Schommer, R.A., Bothun, G.D., Williams, T.B., Mould J.R. 1993}{A. J.}{105}{97}

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