Intrinsic Shapes of Molecular Cloud Cores

We conduct an analysis of the shapes of molecular cloud cores using recently compiled catalogs of observed axis ratios of individual cores mapped in ammonia or through optical selection. We apply both analytical and statistical techniques to deproject the observed axis ratios in order to determine the true distribution of cloud core shapes. We find that neither pure oblate nor pure prolate cores can account for the observed distribution of core shapes. Intrinsically triaxial cores produce distributions which agree with observations. The best-fit triaxial distribution contains cores which are more nearly oblate than prolate.Comment: 20 pages, 10 figures. To appear in ApJ (2001 April 1). Color figures available at http://www.astro.uwo.ca/~cjones/ or http://www.astro.uwo.ca/~basu/pub.htm

Using tidal tails to probe dark matter halos

We use simulations of merging galaxies to explore the sensitivity of the morphology of tidal tails to variations of the halo mass distributions in the parent galaxies. Our goal is to constrain the mass of dark halos in well-known merging pairs. We concentrate on prograde encounters between equal mass galaxies which represent the best cases for creating tidal tails, but also look at systems with different relative orientations, orbital energies and mass ratios. As the mass and extent of the dark halo increase in the model galaxies, the resulting tidal tails become shorter and less massive, even under the most favorable conditions for producing these features. Our simulations imply that the observed merging galaxies with long tidal tails (\sim 50-100 kpc) such as NGC 4038/39 (the Antennae) and NGC 7252 probably have halo:disk+bulge mass ratios less than 10:1. These results conflict with the favored values of the dark halo mass of the Milky Way derived from satellite kinematics and the timing argument which give a halo:disk+bulge mass ratio of \sim 30:1. However, the lower bound of the estimated dark halo mass in the Milky Way (mass ratio \sim 10:1) is still consistent with the inferred tidal tail galaxy masses. Our results also conflict with the expectations of \Omega=1 cosmologies such as CDM which predict much more massive and extended dark halos

A multi-particle model of the 3C 48 host

The first successful multi-particle model for the host of the well-known quasi-stellar object (QSO) 3C 48 is reported. It shows that the morphology and the stellar velocity field of the 3C 48 host can be reproduced by the merger of two disk galaxies. The conditions of the interaction are similar to those used for interpreting the appearance of the ''Antennae'' (NGC 4038/39) but seen from a different viewing angle. The model supports the controversial hypothesis that 3C 48A is the second nucleus of a merging galaxy, and it suggests a simple solution for the problem of the missing counter tidal tail.Comment: 5 pages, 5 figures, accepted for publication in A&

The warp of the Galaxy and the Large Magellanic Cloud

We study the possibility that the Galactic warp is caused by the tides of the Magellanic clouds. Using a specialized N-body particle+ring code we investigate the role of extra torques on the disc induced by gravitational wakes in the dark halo created by the Large Magellanic Cloud. We find that neither the amplitude nor the orientation of the resulting warp agrees with observations

The Origin of the Brightest Cluster Galaxies

Most clusters and groups of galaxies contain a giant elliptical galaxy in their centres which far outshines and outweighs normal ellipticals. The origin of these brightest cluster galaxies is intimately related to the collapse and formation of the cluster. Using an N-body simulation of a cluster of galaxies in a hierarchical cosmological model, we show that galaxy merging naturally produces a massive, central galaxy with surface brightness and velocity dispersion profiles similar to observed BCG's. To enhance the resolution of the simulation, 100 dark halos at $z=2$ are replaced with self-consistent disk+bulge+halo galaxy models following a Tully-Fisher relation using 100000 particles for the 20 largest galaxies and 10000 particles for the remaining ones. This technique allows us to analyze the stellar and dark matter components independently. The central galaxy forms through the merger of several massive galaxies along a filament early in the cluster's history. Galactic cannibalism of smaller galaxies through dynamical friction over a Hubble time only accounts for a small fraction of the accreted mass. The galaxy is a flattened, triaxial object whose long axis aligns with the primordial filament and the long axis of the cluster galaxy distribution agreeing with observed trends for galaxy-cluster alignment.Comment: Revised and accepted in ApJ, 25 pages, 10 figures, online version available at http://www.cita.utoronto.ca/~dubinski/bcg