Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/176374 [Full text of this article is not available in the UHRA]High-resolution H I observations taken at the VLA of the interacting pair of galaxies NGC 2207 and IC 2163 are presented, compared with optical and radio continuum images, and analyzed with detailed computer simulations (in Paper II) in order to determine the orbits and study the effects of in-plane and out-of-plane tidal forcing during a recent, close, nonmerging encounter between galaxies of comparable mass. IC 2163 has an ocular shape (an eye-shaped central oval with a sharp apex at each end) and a double- parallel arm structure on the side opposite NGC 2207. Our observations of IC 2163 find (1) an intrinsically oval shape to the disk, (2) large streaming motions along the oval, (3) H I tidal arms located symmetrically on opposite sides of the nucleus (even though one side is obscured by NGC 2207 at optical wavelengths), and (4) a line-of-sight velocity difference of 70-100 km s-1 between the two components of the double-parallel arm. Optical surface photometry of IC 2163 indicates that most of the stars in the interarm region have been cleared away and put into the central oval and tidal arms. The kinematic and structural anomalies of IC 2163 are consistent with the predictions of N-body galaxy encounter simulations if NGC 2207 moved approximately in the plane of IC 2163 in a prograde sense. The companion, NGC 2207, shows different types of disturbances. The main body of H I gas in NGC 2207 forms a broad, clumpy ring that contains relatively thin stellar arms and corresponds to a plateau in the radial distribution of optical light. The most massive H I clouds in the ring do not always coincide with the stellar arms. The ring is broken in the south, and a filamentary pool of H I extends 40 kpc farther south. The velocity field in the main disk of NGC 2207 is highly distorted with isovelocity contours that are shaped like an open trailing spiral, and the H I line profiles in this region are very broad with Gaussian dispersions of 40-50 km s-1. The kinematic disturbances in NGC 2207 suggest that the main tidal force on NGC 2207 was perpendicular to its disk. The companion side of the H I ring is unusually bright in ??20 cm radio continuum emission, perhaps indicating a shock front. There is no significant excess of star formation in these galaxies, but there are several 108 Msun gas clouds in each disk, some of which may eventually become detached dwarf galaxies
Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/176375 [Full text of this article is not available in the UHRA]Observations of the disturbed morphologies and internal velocity distributions, and of the relative positions, orientations, and centroid velocities of the interacting spiral galaxies IC 2163 and NGC 2207, are reproduced by computer simulations of each galaxy. The ocular morphology of IC 2163, consisting of a bright oval with pointed apices and a double-parallel structure in the tidal arm, as well as the streaming motions along the oval and the arms and the nearly perpendicular alignment of the kinematic and photometric minor axes, are fitted to a model in which IC 2163 is reacting to an in-plane, prograde encounter with NGC 2207 that had a closest approach ??4 ?? 107 yr ago. In NGC 2207, strong velocity anomalies consisting of a global distortion of the velocity distribution into an S shape and a 40 misalignment of the kinematic and photometric minor axes are fitted by a dynamical model in which the companion, IC 2163, moved in a plane perpendicular to the disk of NGC 2207 with the same relative orbit as in the IC 2163 model. The resulting out-of-plane tidal forces are producing a warp of the disk of NGC 2207 with present z-displacements as large as 9 kpc and present z-velocities up to 100 km s-1. The large southern extension of NGC 2207 observed in H I and in optical images is probably a tidal remnant from the time, ??2.4 ?? 108 yr ago, when IC 2163 crossed the western extrapolated plane of NGC 2207 from the near side to the far side, prior to perigalacticon on the far side. The high resolution of both the observations and the models gives an unprecedented view of the dynamics of strong tidal interactions between galaxies
No abstract
One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to define since the bar can change stellar orbits. Many disc galaxies, including the Milky Way, are barred galaxies. The stars in the bar move in a number of fairly complicated orbits. However, the bar will also influence the orbits of stars in the whole galaxy. Stars passing close to the bar can either gain or lose angular momentum, due to a positive or negative torque by the bar. Some stars will therefore be captured by the bar while some stars eventually may reach the escape velocity from the galaxy. The bar will hence be able to relocate stars, and stars with low or high metallicity could be found far away from their original orbits. The ordinary evolution of a bar is to grow in length out to the co-rotation radius for the pattern speed of the bar. As the galaxy ages, and the bar grows in length, the bar will influence a larger part of the galaxy. The effect of moving stars inwards or outwards is greatest just outside the bar, and this region can eventually lose a high percentage of the stars.
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