Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........8h&link_type=abstract
Thesis (PH.D.)--COLUMBIA UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-03, Section: B, page: 1476.
Computer Science
49
Scientific paper
In this thesis I present a multi-wavelength study of five merging disk systems. I directly test the hypothesis that the merger of two atomic gas rich spirals will leave an atomic gas poor elliptical, by measuring the quantities, distribution, and kinematics of the atomic gas along an evolutionary disk-disk merger sequence. These data are supplemented by deep broad band R and narrow band H alpha imaging to completely map the faint stellar distribution and regions of current star formation. I identify several trends along the sequence, the most noteworthy of which are the presence of plumes of ionized gas emanating from the minor-axis in the early stages of merging, and a very low central atomic gas content in the late stage mergers. Overall, large quantities of both gas and starlight are sent to distant radii. Since this material evolves on very long time scales, it may leave observable signatures of the merger for many billions of years. Substructures are found within the expanding tails, with properties which suggested that they might evolve into dwarf-like systems. A complete analysis of one of the systems, the prototypical merger remnant NGC 7252, is presented. A comparison of the gas kinematics and optical and gaseous morphologies suggests that much tidal material remains bound to the system and is presently streaming back into the remnant body. This hypothesis is supported by detailed numerical simulations of the encounter, which successfully reproduce the H scI velocity data. The observations of atomic gas streaming back into the remnant while the remnant body remains atomic gas free, coupled with the fact that this system has photometric properties characteristic of ellipticals, leads us to conclude that some mergers are likely to evolve into elliptical galaxies. The simulation is followed beyond the best fit time to study the future evolution of the merger remnant, and we find that half of the remaining tidal material will fall back towards the remnant within the next few Gigayears. Neutral hydrogen observations should therefore be an effective method for uncovering aged merger remnants. Finally I explore some differences between the archetypical disk-disk mergers and the most luminous infrared galaxies, which are believed to be ongoing mergers. The observations may indicate necessary prerequisites for triggering luminous infrared activity in mergers, such as specific orbital geometries or Hubble types for the progenitors.
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