Engineering topics

The, Lih Sin

Publications and source records attributed to The, Lih Sin.

4 records

NASA NTRS1990

Is the Coma cluster binary dominated?

It is investigated whether the model of an expanding cluster dominated by a massive binary galaxy, first suggested by Valtonen and Byrd (1979), is consistent with optical data on the surface density and velocity dispersion of the Coma cluster. The evolution of this model is simulated for a wide variety of initial conditions. It is found that galaxy counts in the model can be made to agree with observation, but that the observed velocity dispersion profile cannot be reproduced. A number of other arguments suggest that the central galaxies in Coma cannot be as massive as required by the model. This model is not a viable representation of the Coma cluster.

The, Lih Sin↗

NASA NTRS1988

Modified Newtonian dynamics and the Coma cluster

The consistency of Milgrom's theory of modified Newtonian dynamics is checked against optical and X-ray data for the Coma cluster of galaxies. It is found that viable models for the cluster containing no dark matter can be constructed. They require an extensive gaseous atmosphere through which galaxies move on near-radial orbits. The gas temperature is predicted to have a shallow minimum near the cluster center; this structure may conflict with the best X-ray spectra of the cluster.

The, Lih Sin↗

NASA NTRS1988

Is the core of the Coma cluster more massive than we thought?

The paper investigates how the mass distribution and mass-to-light ratio of the Coma cluster are constrained by optical and X-ray observations. The X-ray data of Cowie et al. (1987) suggest that the mass of the cluster core is higher than optical estimates based on the assumption that galaxies trace the mass. The X-ray data do not strongly constrain the mass distribution beyond 2/h50 Mpc and are consistent both with a low total mass for the cluster and with a mass similar to the standard value. The low-mass model requires galaxies in the outer part of the cluster to be on near-circular orbits.

The, Lih Sin↗

NASA NTRS1986

The mass of the Coma cluster

Mass estimate uncertainties for the Coma cluster in position and velocity data for the galaxies are examined under the assumption that mass and galaxy distribution are parallel, on the one hand, and on the other, that the form of the mass distribution is not constrained. While low mass models have all the mass in the cluster core, and require the galaxies to be on or near circular orbits, high mass models are noted to have weakly concentrated mass distributions and primarily radial orbits. It is concluded that galaxy data alone are unlikely to clearly distinguish between these possibilities.

The, Lih Sin↗