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We describe the results of a search for galaxies with large (> 350 km/s) velocity dispersions. The largest systems we have found appear to be the extremes of the early-type galaxy population: compared to other galaxies with similar…
We study galaxy clustering using halo models, where gravitational clustering is described in terms of dark matter halos. At small scales, clustering statistics are dominated by halo density profiles, whereas at large scales, correlations…
A simple way of explaining dark matter without modifying known Standard Model physics is to require the existence of a hidden (dark) sector, which interacts with the visible one predominantly via gravity. We consider a hidden sector…
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic…
We present an analysis of the structures, sizes, star formation rates, and local environmental properties of galaxies at z~4-6, utilising deep Hubble Space Telescope imaging of the Hubble Ultra Deep Field. The galaxies we study are selected…
A perturber may excite a coherent mode in a star cluster or galaxy. If the stellar system is stable, it is commonly assumed that such a mode will be strongly damped and therefore of little practical consequence other than redistributing…
Massive stars are known to have a high multiplicity, with examples of higher order multiples among the nearest and best studied objects. In this paper we study hierarchical multiple systems (an inner binary as a component of a wider binary)…
The dense, clustered environment in which massive stars form can lead to interactions with neighboring stars. It has been hypothesized that collisions and mergers may contribute to the growth of the most massive stars. In this paper we…
We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds.…
Observations show that the underlying rotation curves at intermediate radii in spiral and low-surface brightness galaxies are nearly universal. Further, in these same galaxies, the product of the central density and the core radius…
In this paper we address the question whether star formation is driven by local processes or the large scale environment. To do so, we investigate star formation in collisional debris where the gravitational potential well and velocity…
We use Local Group galaxy counts together with the ELVIS N-body simulations to explore the relationship between the scatter and slope in the stellar mass vs. halo mass relation at low masses, $M_\star \simeq 10^5 - 10^8 M_\odot$. Assuming…
The shapes of individual self-gravitating structures of an ensemble of identical, collisionless particles have remained elusive for decades. In particular, a reason why mass density profiles like the Navarro-Frenk-White or the Einasto…
Recent progress is summarized on the determination of the density distributions of stars and dark matter, stellar kinematics, and stellar population properties, in the extended, low surface brightness halo regions of elliptical galaxies.…
Large galaxies are thought to form hierarchically, from the accretion and disruption of many smaller galaxies. Such a scenario should naturally lead to galactic phase-space distributions containing some degree of substructure. We examine…
High-resolution N-body simulations of dark matter halos indicate that the Milky Way contains numerous subhalos. When a dark matter subhalo passes in front of a star, the light from that star will be deflected by gravitational lensing,…
Observations and cosmological simulations indicate that the early Universe hosted numerous compact, high-density stellar systems, where close encounters and physical collisions between stars were likely common. We develop a bottom-up…
Large-scale sky surveys require companion large volume simulated mock catalogs. To ensure precision cosmology studies are unbiased, the correlations in these mocks between galaxy properties and their large-scale environments must be…
We present the first results from the largest H$\alpha$ survey of star formation and AGN activity in galaxy clusters. Using 9 different narrow band filters, we select $>3000$ H$\alpha$ emitters within $19$ clusters and their larger scale…
We investigate a hypothesis regarding the origin of the scalelength in halos formed in cosmological N-body simulations. This hypothesis can be viewed as an extension of an earlier idea put forth by Merritt and Aguilar. Our findings suggest…