Visualization of Numerical
Simulations with YView
Raúl Sevilla (1), Yago Ascasíbar (2) & Gustavo Yepes(1)
(1)
Grupo de Astrofísica. Universidad Autónoma de Madrid
(2) Harvard-Smithsonian Center for Astrophysics
BASICS OF YView
DATA REPRESENTATION
Yview is a FORTRAN -based program intended to interactively visualize and analyze th e results of
numerical simulations. It provides plots in real time through a user -friendly interface, being able to
handle a large number of particles with minimum hardware requirements (a simulation with 3 million
particles requires about 70 Mbytes of memory). It makes use of PGPLOT and BUTTON graphical
libraries, which work in a wide variety of computers and operating systems. The only limitation comes
from the memory available to allocate particle data on your part icular station.
YView can draw arbitrary distributions of
gas, dark matter, gas temperature (either
mass-weighted or X-ray emission -weighted)
and X-Ray luminosity, computed according
to the thermal bremsstrahlung tables of
Sunderland & Dopita (1993). Additional
support for star particles is provided if
appropriate.
The graphical output is divided in 2 regions: the plot region and the menu panels. In the former, images
are represented (using the current color palette) with some information regarding their coordinates,
redshift and number particles. The latter uses the BUTTON library to han dle most of YView's interactive
capabilities.
The program reads 3D-data in GADGET
(Springel et al. 2001) and ART (K ratsov et al.
1999) native formats, and builds three 2-D grids
corresponding to the orthogonal projections
along the main axes. Each grid is generated
from the particle distribution using different
interpolation schemes (NGP, CIC, etc), thus
obtaining a CCD-like image of the numerical
data.
Data representation can be either in color maps or contour
plots, allowing simultaneous plots of two different
magnitudes. Dark matter halos from object identification
algorithms can be plotted on top of the images. Only the
output formats of HOT (Ascasibar et al., in prep.) and
BDM (Klypin et al. 1999) are currently implemented.
UTILITIES
Several utilities are included within the
graphical interface. Box selection is mostly
controlled by clicking on the plot region, while
the rest of the tools are located on the menu
panel: saving to a GIF image, overplotting
halo catalogs, enabling/disabling projection
effects, change color palette settings, etc.
FUTURE IMPROVEMENTS
Enabling projection effects may cause spurious
objects along the line-of-sight to appear in the plot.
Above, we show how disabled (left) and enabled
(right) projections effects and the appearance of an
extra object in one projection.
The choice of a color palette allows custom
visual adjustments. Different regions of interest
can be highlighted with the 6 palettes already
included in Yview. Brightness, contrast and
range can be modified at will in order to achieve
the desired visual effect.
Left panels show the dark matter distribution of two
different galaxy clusters using 5 different palettes.
According to the color palette employed, either the
central region or the substructure is being focused.
For instance, on the upper right corner low-mass
objects around the core are stressed. The middle left
image features the innermost core, whereas the
middle left highlights the filaments.
The CCD-like treatment of images is an advantage for direct comparison between simulations
and observations of real objects. With minor changes in the code, grid resolution can be
adaptable during execution. This will make it possible to obtain mock CCD images of
simulated objects as observed by current X-ray satellites (Gardini et al. 2004). Mock images in
other bands can also be easily obtained from simulations including a star formation
prescription.
Diferent file formats should be incorporated to Yview. Of particular interest is the capability of
recording FITS files, which could be then analyzed with standard astrophysical packages
(IRAF, MIDAS, etc) in a manner entirely analogous to their observational counterparts.
REFERENCES
• Ascasibar et al., in preparation
• BUTTON: http://www.ucm.es/info/Astrof/software/button/button.html
• Gardini A., et al., 2004, MNRAS, 351, 505
• Klypin A.,et al. 1999, ApJ, 516, 530
• Kravtsov A., Klypin A., Khokhlov A. 1997, ApjS, 111, 73
• PGPLOT: http://www.astro.caltech.edu/~tjp/pgplot/
• Sunderland & Dopita, 1993, ApJS, 88, 253
• Springel V., Yoshida N. White S.D.M., 2001, NewA, 6, 79
• YVIEW web page: http://astro.ft.uam.es/YView/