Merging Scenario Research Articles

Magnetization of the Intergalactic Medium by Primeval Galaxies

We review what has recently been learned from starburst-driven superwinds, galaxy-scale outflows, dwarf galaxy surveys, and evidence for early-universe merging scenarios. We apply this knowledge to simplified model populations of dwarf galaxies in the primeval galaxy era to demonstrate how a substantial fraction of the intergalactic medium can be permeated with magnetic fields by dwarf galaxy outflow winds in the volcanic early Mechanisms of both magnetic field regeneration and diffusion are discussed as they apply to galaxies at both primeval and later epochs of the universe. We propose that, in the past, magnetic field strengths in outflow superbubbles and halos were stronger than those now prevailing in the disks of current-epoch galaxies such as the Milky Way. We also show how subsequent acausal diffusion of magnetic fields (which we have not modeled) can propagate the fields over great distances in the universe within a Hubble time. We conclude that dwarf galaxies can effectively seed the intergalactic medium with magnetic fields for a wide range of outflow and galaxy density parameters. If the first galaxies form at or before z~10 in a bottom-up hierarchical merging scenario, a substantial fraction of the intergalactic medium will become permeated with a magnetic field at the present epoch. This intergalactic field seeding is largely accomplished by z~6.

Microscopic Simulation Analysis for Automated Highway System Merging Process

The automated highway system (AHS) concept with dedicated lanes is not designed as a stand-alone transportation facility. Drivers will by necessity need to drive from their origins to the AHS entrance and from the AHS exit to their final destinations. Therefore, the AHS will affect other transportation facilities and will need to be integrated with all other facilities in the transportation system. Interfaces create much of the congestion for today’s transportation systems. AHS interfaces may cause similar problems, as a result of either AHS interactions with conventional systems or internal limitations from AHS merging capabilities. If these problems exist, either the AHS or the conventional road network cannot function properly. Then the system as a whole will break down, and the AHS could prove a detriment to the overall transportation system. Clearly not enough is known about the automated merging process to determine what conditions would lead to congestion at interface points. Current macroscopic techniques assume parameters that are not applicable to an AHS, and no detailed AHS merging models have been developed and validated. The AHS to conventional roadway interface problem is addressed by presenting a microscopic simulation model for one scenario of the automated merging maneuver. Some numerical results are presented for this merging scenario.

Early versus late type galaxies in compact groups

AbstractWe find a strong correlation between the effective radius of the largest early‐type galaxies in compact groups of galaxies and the velocity dispersion of the groups. The lack of a similar correlation for late type galaxies is supportive of the so called second generation merging scenario which predicts that ellipticals should dominate the internal dynamics of the groups, while late‐type galaxies are mainly recent interlopers which are still in an early stage of interaction with the group potential.

After NAFTA: Western hemisphere trade liberalization and alternative paths to integration

Several alternative paths have been proposed for extending the current system of Western Hemisphere sub-regional trade agreements into a more comprehensive scheme of hemispheric integration. The scenarios of NAFTA accession, hub-and-spoke arrangements and trade agreement merging, are analyzed, including incentives for and barriers to each path. Patterns of recent negotiation activity, as well as the strong requirements for NAFTA accession, imply that trade agreement merging is currently the most probable scenario.

Dust and infrared imaging of polar ring galaxies

We have derived surface photometry for a sample of five polar ring (PR) galaxies in the optical (B and R bands) and in the near-IR (K band). Our preliminary results show that the morphology of these objects is heavily perturbed by dart, which sometimes completely hides the real distribution of the older stellar population. The analysis of the colour profiles and of the integrated colours of the host galaxy and polar ring in these systems indicates that (1) the ring and the central galaxy appear to have different stellar populations, which supports the accretion /merging scenario for these objects, and (2) although the host galaxies have an early-type morphology, their integrated colours are close to those of spirals, with a strong blueward colour gradient from the centre outward.

Modelling evolution of stellar emission of galaxies for the nir surveys

Recent observational results in the near-IR on distant galaxies and interacting galaxies are clues for modelling evolution of galaxy counts and for testing theories of galaxy formation. Spectrophotometric models, developed in the ultraviolet and visible, were tools essential for such interpretations. So we hereafter present their extension to the near-infrared and preliminary results on radiogalaxies, starbursts and faint counts. The two fundamental objectives are to confirm a merging scenario and to determine the age of the first stellar generation.

Galaxy mergers and gravitational lens statistics

We investigate the impact of hierarchical galaxy merging on the statistics of gravitational lensing of distant sources. Since no definite theoretical predictions for the merging history of luminous galaxies exist, we adopt a parametrized prescription, which allows us to adjust the expected number of pieces comprising a typical present galaxy at z=0.65. The existence of global parameter relations for elliptical galaxies and constraints on the evolution of the phase space density in dissipationless mergers, allow us to limit the possible evolution of galaxy lens properties under merging. We draw two lessons from implementing this lens evolution into statistical lens calculations: (1) The total optical depth to multiple imaging (e.g. of quasars) is quite insensitive to merging. (2) Merging leads to a smaller mean separation of observed multiple images. Because merging does not reduce drastically the expected lensing frequency it cannot make $\lambda$-dominated cosmologies compatible with the existing lensing observations. A comparison with the data from the HST Snapshot Survey shows that models with little or no evolution of the lens population are statistically favored over strong merging scenarios. The specific merging scenario proposed by Toomre (1977) can be rejected (95\% level) by such a comparison. Some versions of the scenario proposed by Broadhurst, Ellis \& Glazebrook (1992), are statistically acceptable.

Can elliptical galaxies be formed by merging of spirals?

Summary It is shown, on the basis of the mixing theorem, that normal elliptical galaxies cannot form through dissipationless merging of pure stellar discs, but that the inclusion of a modest bulge component in the disc galaxy models overcomes the problem with respect to phase space density constraints. The bulge-to-disc ratios required are found to be in the range 0.1—0.5; the smaller the systems, the higher the bulge-to-disc ratio needed. We stress that not only phase space density, but also space density constraints, are of relevance in the dissipationless merging scenario.

Alignment of cD-Galaxies with their Surroundings

AbstractFor a sample of 122 rich Abell clusters we find a strong correlation of the position angle (orientation) of the first-ranked galaxy and its parent cluster. This alignment effect is strongest for cD-galaxies. Formation scenarios for cD galaxies, like the merging scenario, must produce such a strong alignment effect. We show some N-body simulations done for this purpose.