The mass of the Coma cluster

The authors examine the uncertainties in mass estimates for the Coma cluster derived from position and velocity data for the galaxies. If the mass distribution is assumed to parallel the galaxy distribution, the total mass within 5.4h₅₀⁻¹ Mpc is 1.9×10¹⁵h₅₀⁻¹M_sun; to an accuracy of about 30% (for H₀ = 50 h₅₀ km/s/Mpc). However, if the form of the mass distribution is not constrained, the total mass in this region can range between 6×10¹⁴h₅₀⁻¹ M_sun; and 5×10¹⁵h₅₀⁻¹ M_sun;. Low-mass models have all the mass in the cluster core and require the galaxies to be on near circular orbits. High-mass models have weakly concentrated mass distributions and primarily radial orbits. Galaxy data alone are unlikely to be able to distinguish between these possibilities.