Computer Science – Numerical Analysis
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...280..383m&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 280, no. 2, p. 383-399
Computer Science
Numerical Analysis
21
Astronomical Models, Dynamic Characteristics, Interacting Galaxies, Kinematics, Numerical Analysis, Observation, Radio Jets (Astronomy), Velocity Distribution, Energy Distribution, Luminosity, Mass Distribution, Mathematical Models, Morphology, Perturbation, Star Distribution, Velocity Measurement
Scientific paper
We have investigated a number of self-consistent numerical experiments of encounters of spherical and isotropic, non-rotating model galaxies using Superbox, an extension of the conventional particle-mesh technique. Each model galaxy consists of 50,000 stars and has initially an r0.25 luminosity profile. A special high-velocity hyperbolic and deeply interpenetrating encounter (Vmax/sigma = 4.8, bmin = 0.56 Re) which under oblique view yields the best agreement with the observational data on NGC 4782/3, is selected and investigated in detail. Stars are most strongly distributed on that side of either galaxy where the other galaxy center passes. When these stars reach the other, far side, they have much higher kinetic energy than they would have in the unperturbed case. Thus the velocity distribution after closest approach on the far side is much broader than before, perturbing the initially spherical mass distribution. During the phase of interpenetration of the two galaxies, the centers and envelopes see different time-varying mass distributions, so that the centers are displaced relative to their envelopes. From the time required for the displaced centers to return to their original central positions, the efficiency of dynamical friction is estimated. The luminosity profiles develop on local dynamical timescales and thus allow an accurate estimate of the time elapsed since closest approach. During the encounter 31% of initial orbital energy of the galaxies is transferred into internal energy. Mass loss is estimated to 1/7 of the initial mass with most escaping stars coming from regions outside 2 Re. The number of stars exchanged between the two galaxies is negligible (below 1%). For this encounter the peculiar morphology of NGC 4782/3 is well reproduced 0.5 crossing times or, when scaled to the observational data, 13.5 Myr after closest approach, with the line of sight inclined by 50 deg with respect to the orbital plane. Radially increasing velocity dispersion is found and a map is constructed, in good agreement with the earlier presented velocity dispersion map of NGC 4782/3. However, in a simple scenario based on the above conventional numerical experiments, the origin of the peculiar morphology of the bending east radio jet of 3C 278 (NGC 4782) remains controversial.
Bien Reinhold
Madejsky Rainer
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