Spiral Galaxy Mass Models using Fabry-Perot Velocity Maps

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Session 6 -- Normal Galaxies: Structure and Dynamics
Display presentation, Monday, 9:20-6:30, Pauley Room

[6.04] Spiral Galaxy Mass Models using Fabry-Perot Velocity Maps

P.Palunas, T.B.Williams (Rutgers University), R.A.Schommer (CTIO)

\def\kms{$\rm {km}~\rm s^{-1}$} We present mass models for a sample of spiral galaxies taken from the southern sky Fabry-Perot Tully-Fisher survey. The survey consists of approximately 200 galaxies, each with $I$-band and either $R$- or $V$-band CCD photometry, and a series of 8-20 narrow-band images spaced at approximately 50 \kms$~$ intervals covering the H$\alpha$ emission line. The broad-band observations, made with the CTIO 0.9m telescope, extend to $\sim$4 disk scale lenths in the I-band. The narrow-band observations were made with the CTIO 1.5m telescope using the Rutgers Imaging Fabry-Perot Interferometer with a resolution of 100 \kms$~$ (FWHM) at H$\alpha$. Fitting the wavelength of the H$\alpha$ line at each spatial resolution element in these images yields 2-d velocity maps out to the same radial scale as the I-band photometry. The velocity precision is $\sim$3 \kms$\;$ in bright HII regions and $\sim$15 \kms$\;$ at the faintest measurable points.

Fitting a tilted ring model to each velocity map yields a rotation curve (in the final fit the kinematic inclination, position angle and center are fixed at their average values). We fit a 2-d photometric model consisting of a concentric deVaucouleurs bulge and an exponential disk to each $I$-band image. The disk and bulge each have four parameters: central surface brightness, major-axis scale length, ellipticity and position angle. Fitting to the full 2-d images allows the models to be seeing corrected and helps constrain the disk-bulge deconvolution by using the information in the different ellipticities and position angles as well as the different radial profiles of the disk and 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. Finally, the photometric model is fit to the rotation curve assuming a maximum disk and constant mass-to-light ratios for each component. The small scale structure in the photometric model is found to reproduce the structure in the rotation curve.

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