Local Group timing argument and virial theorem mass estimators from cosmological simulations
Abstract
We identify Local Group (LG) analogues in the IllustrisTNG cosmological simulation, and use these to study twomass estimators for the LG: One based on the timing argument (TA) and one based on the virial theorem (VT). Including updated measurements of the Milky WayM31 tangential velocity and the cosmological constant, we show that the TA mass estimator slightly overestimates the true median LGmass, though the ratio of the TA to the true mass is consistent at the approximate 90 per cent c.l.. These are in broad agreement with previous results using dark matteronly simulations. We show that the VT estimator better estimates the true LGmass, though there is a larger scatter in the virial mass to true mass ratio relative to the corresponding ratio for the TA. We attribute the broader scatter in the VT estimator to several factors, including the predominantly radial orbits for LG satellite galaxies, which differs from the VT assumption of isotropic orbits. With the systematic uncertainties we derive, the updated measurements of the LG mass at 90 per cent c.l. are $4.75_{2.41}^{+2.22} \times 10^{12}$ M_{⊙} from the TA and $2.0_{1.5}^{+2.1} \times 10^{12}$ M_{⊙} from the VT. We consider the LMC's effect on the TA and VT LG mass estimates, and do not find exact LMCMWM31 analogues in the Illustris simulations. However, in LG simulations with satellite companions as massive as the LMC, we find that the effect on the TA and VT estimators is small, though we need further studies on a larger sample of LMCMWM31 systems to confirm these results.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2022
 DOI:
 10.1093/mnras/stac413
 arXiv:
 arXiv:2107.11490
 Bibcode:
 2022MNRAS.511.6193H
 Keywords:

 galaxies: kinematics and dynamics;
 (galaxies:) Local Group;
 (cosmology:) dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 12 pages, 6 figures, Accepted for publication in MNRAS