Galaxy Collisions and Star Formation

In this review, I present the case for how massive stars may form through stellar collisions. This mechanism requires very high stellar densities, up to 4 orders of magnitude higher than are observed in the cores of dense young clusters. In this model, the required stellar densities arise due to gas accretion onto stars in the cluster core, including the precursers of the massive stars. This forces the core to contract until the stellar densities are sufficiently high for col...

We utilize magnetohydrodynamic (MHD) simulations to develop a numerical model for GMC-GMC collisions between nearly magnetically critical clouds. The goal is to determine if, and under what circumstances, cloud collisions can cause pre-existing magnetically subcritical clumps to become supercritical and undergo gravitational collapse. We first develop and implement new photodissociation region (PDR) based heating and cooling functions that span the atomic to molecular transit...

We review the physics of star formation, and its links with the state of the ISM in galaxies. Current obervations indicate that the preferred mode of star formation is clustered. Given that OB associations provide the dominant energy input into the ISM, deep links exist between the ISM and star formation. We present a multi-scale discussion of star formation, and attempt to create an integrated vision of these processes.

In this paper we demonstrate for the first time the connection between the spatial and temporal progression of star formation and the changing locations of the very dense regions in the gas of a massive disk galaxy (NGC 1144) in the aftermath of its collision with a massive elliptical (NGC 1143). These two galaxies form the combined object Arp 118, a collisional ring galaxy system. The results of 3D, time-dependent, numerical simulations of the behavior of the gas, stars, and...

Modelling global disc galaxies is a difficult task which has previously resulted in the small scale physics of the interstellar medium being greatly simplified. In this talk, I compare simulations of galaxies with different ISM properties to determine the importance of the ISM structure in the star formation properties of the disc.

Using N-body and SPH modeling we perform 3D numerical simulations of head-on collisions between gas rich disk galaxies, including collisions between counter-rotating disks and off-center collisions. Pure stellar intruders do not produce gaseous plumes similar to those seen in the Cartwheel and VII Zw466 complexes of interacting galaxies; the presence of gas in an intruder galaxy and radiative cooling are important for the formation of a gaseous plume extending from the disk o...

Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectivel...

The strong tidal force in a supermassive black hole's (SMBH) vicinity, coupled with a higher stellar density at the center of a galaxy, make it an ideal location to study the interaction between stars and black holes. Two stars moving near the SMBH could collide at a very high speed, which can result in a high energy flare. The resulting debris can then accrete onto the SMBH, which could be observed as a separate event. We simulate the light curves resulting from the fallback...

Centers of galaxies host both a supermassive black hole and a dense stellar cluster. Such an environment should lead to stellar collisions, possibly at very high velocities so that the total energy involved is of the same order as supernovae explosions. We present a simplified numerical analysis of the destructive stellar collision rate in a cluster similar to that of the Milky Way. The analysis includes an effective average two-body relaxation Monte-Carlo scheme and general ...

We demonstrate that single and binary star clusters can be formed during cloud-cloud collisions triggered by the tidal interaction between the Large and Small Magellanic clouds. We run two different sets of self-consistent numerical simulations which show that compact, bound star clusters can be formed within the centers of two colliding clouds due to strong gaseous shocks, compression, and dissipation, providing the clouds have moderately large relative velocities (10-60 km ...