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VI/76     Simulation Atlas of Tidal Features in Galaxies     (Howard+ 1993)

A Simulation Atlas of Tidal Features in Galaxies Howard S., Keel W.C., Byrd G.G., Burkey J. <Astrophys. J. 417, 502 (1993)> =1993ApJ...417..502H
ADC_Keywords: Morphology; Galaxies, peculiar; Models Abstract: The simulation survey of tidally perturbed galaxies provides images of 84 different encounters that vary orbit tilt of companion orbit, perigalacticon distance ratio of primary galaxy mass to companion mass, and the amount of inert matter in the primary galaxy. In total 1764 galaxy images are available in the survey. This data set contains 84 separate simulations, each simulation is run for 1000 time steps, producing image output of the star particles and gas particles separately every 50 time steps. The first 21 images represent the "gas", and the second 21 images represent the "stars". Time steps for matching "gas" and "stars" are the same. There are [256,256] grid points on a Cartesian coordinate system. The renormalized densities are stored as 8-bit floating point numbers. The data have been put into FITS. Each header specifies the parameters for that simulation. Introduction: The simulation atlas provides an image dictionary of simulations that span several encounter parameters with fine morphological resolution and includes the effects of self-gravitation. Observers and theorists can then search the dictionary for the parameters that best match a particular observed morphology. The survey uses a self-gravitating, 180,000 particle, two-component ("stars" and "gas") disk with an inert halo. The companion follows a fully 3D self-gravitating orbit. The disk is constrained to two dimensions. The "star" data and the "gas" data are stored as separate images. The n-body code has a polar-coordinate grid especially well suited to simulate disk galaxies. The grid is exponentially spaced in the radial direction and provides increasing resolution from edge to center. Each bin has a constant angular size as seen from the origin. There are 24 radial and 36 azimutal bins which give an effective resolution that matches a 720x720 Cartesian grid. The code combines the speed of a particle mesh code with tree aspects for fine tuned handling of the companion orbit. The code is stable against intrinsic small perturbations. The initial potential for the disk is a finite Mestel (1963) disk which produces a flat rotation curve. The halo is represented by an inert potential set to match the value of the Mestel potential in the disk. The contribution of this potential is either equal to the potential of one disk mass or ten times the potential of one disk mass. Of the 180,00 particles, 126,000 of the are "stars", each having a velocity dispersion in the disk plane that ensures stability against axisymmetric perturbations. The remaining 54,000 "gas" particles have an initial velocity dispersion of 0.0. The particles are not allowed to collide. The initial velocity of the companion is set to match a zero energy orbit. The initial position is far enough away to assure a clean passage. The companion is treated as a point mass. Each simulation runs for 1000 time steps. With 50 steps per crossing time (one crossing time is the time a particle takes to travel a distance of one disk radius traveling at the initial circular orbital speed), there are 314 time steps for one galactic rotation. Assuming a typical disk radius of 20kpc, and a disk orbital speed of 200 km/s, one time step corresponds to about 1.5 million years. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file params.dat 30 168 Summary of models, see "Introduction" section above fits/* 0 168 FITS files (21 images per file) with the models
Byte-by-byte Description of file: params.dat
Bytes Format Units Label Explanations
1- 11 A11 --- FileName *Name of file, in "fits" subdirectory 14- 15 I2 --- N3 *[21] Number of images in the simulation 17- 18 I2 deg i *Inclination angle of the companion's orbit 20- 22 F3.1 --- Mratio *Mass ratio of companion to primary 24 I1 --- Rad *[1,2] Closest approach of companion 26- 27 I2 --- Mhalo [1,2] Halo to disk mass ratio (dark matter) 30 A1 --- Rot [PR] Pro- or Retro-grade rotation
Note on FileName: there are two files for each of the 84 models, one starting by 'g' for the gas contents, and another one starting by 's' for the stellar contents; see the "Introduction" section above. Note on N3: each image corresponding to a time increase of about 1.5Myr, see the "Introduction" section above. Note on i: the values are 0, 30, 60, 89 degrees. Note on Mratio: the values are 0.1, 0.5, 1.0 Note on Rad: distance of closest approach of companion in terms of galaxy disk radius Ren/Rg: 1=grazing encounter, 2=distant encounter
Content of the Atlas: The original Atlas contains 86 separate simulations. The 2 simulations with no companion present that were used for testing the stability of the code are absent in this distribution. Each simulation is run for 1000 time steps, producing image output (an image of the star particles and an image of the gas particles) every 50 time steps. The code stores the gas particles and the star particles separately. This data set does not combine them. Therefore, each simulation contains 21 "gas" images and 21 "star" images. The time steps for matching "gas" and "star" images are the same. Each image is stored as a floating point array [256,256]. Each cell contains a scaled floating point number that represents the number of particles in that cell. The data are written as FITS files. The scaling algorithm was chosen to maximize contrast for image display units. The cell containing the companion is set to 35,000 always. Where the zero count is zero, the cell contains the number 0.0. Where the count is non-zero, the cell contains a value of Value = N*64000/(max cell count for that image) + 2048, where N is the particle count for that cell. The files are listed in the File Summary above. The file name start by the letter "s" or "g" as appropriate and the letter i followed by the inclination of the companion orbit (in degrees) followed by a running letter. When the letter "r" follows that letter, the rotation is a retrograde orbit. When there is no letter "r" the simulation follows a prograde passage of the companion. The parameter ranges are: - the companion orbit has inclinations of 0, 30, 60, 89 deg. - ratio of halo mass to disk mass (dark matter test) = 1 and 10 - distance of closest approach of companion = 1 and 2 (in terms of galaxy disk radius Ren/Rg 1=grazing encounter, 2=distant encounter) - ratio of companion mass to primary mass = 0.1, 0.5, 1.0 The parameter ranges are listed in the file "params.dat" References: Mestel, L. 1993, Mon. Not. R. Astron. Soc. V. 126, p. 553. =1963MNRAS.126..553M The data were also published on the second ApJ video edition accompanying the published paper.
(End) N. Paul M. Kuin [NASA/NSSDC/ADC] 1995-01-31
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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