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Session 105 - Galaxies: Counts & Kinematics.
Display session, Saturday, January 10
Exhibit Hall,
The Tully-Fisher (TF) relation between rotation velocity and luminosity is one of the strongest correlations for disk galaxies. Consequently, the TF relation has great potential as a tool for measuring galaxy evolution, namely to trace changes in the total M/L of disk galaxies with look-back time. Because of the steep slope in the TF relation, however, small errors in measured velocity result in large uncertainties in the inferred luminosity. We present estimates of the amplitude of random and systematic errors in measured optical rotation velocities of distant galaxies based on HII-region line emission (e.g. H\alpha). Our simulations use realistic kinematic galaxy models with emission distributed non-uniformly, i.e. with concentrations in spiral arms and star-forming knots. The simulations include the effects of finite slit widths, image blur, random noise, and position angle and centroid uncertainties. The resulting analysis yields an estimate for a substantial component of the Tully-Fisher error-budget as applied to distant galaxy observations. Other components of the error budget involve inclination and extinction corrections, and the quality of the template sample used to define a fiducial relation. Here, we estimate the amplitude of the errors in inferred luminosity due velocity measurements alone, and compare them to the expected changes in luminosity with look-back time due to varying cosmologies and passive evolution.
