Testing a simple recipe for estimating galaxy masses from minimal observational data

Abstract

The accuracy and robustness of a simple method to estimate the total mass profile of a galaxy are tested using a sample of 65 cosmological zoom simulations of individual galaxies. The method only requires information on the optical surface brightness and the projected velocity dispersion profiles, and therefore can be applied even in the case of poor observational data. In the simulated sample, massive galaxies (σ≃ 200-400kms-1) at redshift z= 0 have almost isothermal rotation curves for broad range of radii (rms ≃ 5per cent for the circular speed deviations from a constant value over 0.5Reff < r < 3Reff). For such galaxies, the method recovers the unbiased value of the circular speed. The sample-averaged deviation from the true circular speed is less than ∼1per cent with the scatter of ≃5-8per cent (rms) up to R≃ 5Reff. Circular speed estimates of massive non-rotating simulated galaxies at higher redshifts (z= 1 and 2) are also almost unbiased and with the same scatter. For the least massive galaxies in the sample (σ < 150 kms-1) at z= 0, the rms deviation is ≃7-9per cent and the mean deviation is biased low by about 1-2per cent. We also derive the circular velocity profile from the hydrostatic equilibrium (HE) equation for hot gas in the simulated galaxies. The accuracy (rms) of this estimate is about 4-5per cent for massive objects (M > 6.5 × 1012M⊙) and the HE estimate is biased low by ≃ 3-4per cent, which can be traced to the presence of gas motions. This implies that the simple mass estimate can be used to determine the mass of observed massive elliptical galaxies to an accuracy of 5-8per cent and can be very useful for galaxy surveys. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.