Transformations of Galaxies. II. Gasdynamics in Merging Disk Galaxies

Abstract

In mergers of disk galaxies, gas plays a role quite out of proportion to its relatively modest contribution to the total mass. To study this behavior, we have included gasdynamics in self-consistent simulations of collisions between equal-mass disk galaxies. The large-scale dynamics of bridge-and tail-making, orbit decay, and merging are not much altered by the inclusion of a gaseous component. However, tidal forces during encounters cause otherwise stable disks to develop bars, and the gas in such barred disks, subjected to strong gravitational torques, Ñows toward the central regions where it may fuel the kiloparsec-scale starbursts seen in some interacting disk systems. Similar torques on the gas during the Ðnal stages of a collision yield massive gas concentrations in the cores of merger remnants, which may be plausibly identiÐed with the molecular complexes seen in objects such as NGC 520 and Arp 220. This result appears insensitive to the detailed microphysics of the gas, provided that radiative cooling is permitted. The inÑowing gas can dramatically alter the stellar morphology of a merger remnant, apparently by deepening the potential well and thereby changing the boundaries between the major orbital families.

Peculiarities and populations in elliptical galaxies

“…5. A merger involving two spirals is necessarily accompanied by a starburst when part of the ISM collapses towards the center of the main object (Barnes & Hernquist 1996;Mihos & Hernquist 1996). Empirical arguments to this effects were found in the CO observations (Dupraz & Casoli 1991;Combes et al 1994) or in the study of the This summary indicates that a large variety of possible mergers involving different progenitors, S, S0 and even E, may produce the morphological peculiarities and the starbursts revealed in the juvenile population.…”

The Fueling and Evolution of AGN: Internal and External Triggers

“…The first challenge in measuring the masses of IMBHs is that the gravitational radii of such BHs are typically too small to be easily resolved even with HST . A second complication is that late-type spirals and dwarf galaxies which might harbor such BHs also tend to host a bright 10 6 -10 7 At many levels, measuring BH masses in local AGN such as Seyferts and LINERS is more challenging than corresponding measurements in massive quiescent galaxies. The bright non-thermal active nucleus in Seyfert galaxies can drown the spectroscopic features from which dynamical measurements are made.…”

Numerical Simulations of KPG 302 (NGC 3893/96)

“…We use a model of galaxy similar to the one described in Barnes & Hernquist (1996). The model considers three types of matter: stars, dark matter, and interstellar gas.…”