Fabricant, Daniel, Chilingarian, Igor, Seong Hwang, Ho, Kurtz, Michael J., Geller, Margaret J., Del''Antonio, Ian P., and Rines, Kenneth J. 2013. "Measuring Galaxy Velocity Dispersions with Hectospec." Publications of the Astronomical Society of the Pacific 125:1362-1369. https://doi.org/10.1086/673499
We describe a robust technique based on the ULySS IDL code for measuring velocity dispersions of galaxies observed with the MMT''s fiber-fed spectrograph, Hectospec. This procedure is applicable to all Hectospec spectra having a signal-to-noise ratio ≳5 and weak emission lines. We estimate the internal error in the Hectospec velocity dispersion measurements by comparing duplicate measurements of 171 galaxies. For a sample of 984 galaxies with a median z = 0.10, we compare velocity dispersions measured by Hectospec through a 1.5″ diameter optical fiber with those measured by the Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectral Survey (BOSS) through 3″ and 2″ diameter optical fibers, respectively. The systematic differences between the Hectospec and the SDSS/BOSS measurements are -1; the differences are no larger than the differences among the three BOSS velocity dispersion reductions. We analyze the scatter about the fundamental plane and find no significant redshift-dependent systematics in our velocity dispersion measurements to z ˜ 0.6. This analysis also confirms our estimation of the measurement errors. In 1 hr in good conditions, we demonstrate that we achieve 30 km s-1 velocity dispersion errors for galaxies with an SDSS r fiber magnitude of 21.