Weighing the galactic disc using the Jeans equation: lessons from simulations

Candlish, G. N.; Smith, R.; Moni Bidin, C.; Gibson, B. K.

Abstract

Using three-dimensional stellar kinematic data from simulated galaxies, we examine the efficacy of a Jeans equation analysis in reconstructing the total disk surface density, including the dark matter, at the ‘Solar’ radius. Our simulation data set includes galaxies formed in a cosmological context using state-of-the-art high-resolution cosmological zoom simulations, and other idealized models. The cosmologically formed galaxies have been demonstrated to lie on many of the observed scaling relations for late-type spirals, and thus offer an interesting surrogate for real galaxies with the obvious advantage that all the kinematical data are known perfectly. We show that the vertical velocity dispersion is typically the dominant kinematic quantity in the analysis, and that the traditional method of using only the vertical force is reasonably effective at low heights above the disk plane. At higher heights the inclusion of the radial force becomes increasingly important. We also show that the method is sensitive to uncertainties in the measured disk parameters, particularly the scalelengths of the assumed double exponential density distribution, and the scalelength of the radial velocity dispersion. In addition, we show that disk structure and low number statistics can lead to significant errors in the calculated surface densities. Finally, we examine the implications of our results for previous studies of this sort, suggesting that more accurate measurements of the scalelengths may help reconcile conflicting estimates of the local dark matter density in the literature.

Citation

Candlish, G. N., Smith, R., Moni Bidin, C., & Gibson, B. K. (2016). Weighing the galactic disc using the Jeans equation: lessons from simulations. Monthly notices of the Royal Astronomical Society, 456(4), 3456-3474. https://doi.org/10.1093/mnras/stv2792

• Journal Article Type: Article
• Acceptance Date: Nov 25, 2015
• Online Publication Date: Jan 14, 2016
• Publication Date: Mar 11, 2016
• Deposit Date: Apr 1, 2016
• Publicly Available Date: Nov 23, 2017
• Journal: Monthly notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 456
• Issue: 4
• Pages: 3456-3474
• DOI: https://doi.org/10.1093/mnras/stv2792
• Keywords: Gravitation -- methods; Numerical -- galaxies; Kinematics and dynamics
• Public URL: https://hull-repository.worktribe.com/output/434577
• Publisher URL: http://mnras.oxfordjournals.org/content/456/4/3456
• Additional Information: Copy of article first published in: Monthly notices of the Royal Astronomical Society, 2016, v.456, issue 4