CLI Examples

Velocity Dispersion

  • To compute the directional projection statistics for all stars in a snapshot named snapshot_file_name

    $ gsnap snapshot_file_name
  • To compute directional velocity dispersion statistics on an arbitrary combination of particle types:

    $ gsnap -t ###### snapshot_file_name

    where the ###### is a six-character type specification string. Place a ’1′ in the specification string to specify that you want to include. The meaning of each of the 6 entries are:

    0: gas / SPH particles
    1: dark matter particles
    2: disk particles
    3: bulge particles
    4: new star particles
    5: black hole particles

    For example, to specify all stellar particles, we would use,

    $ gsnap -t 001110 snapshot_file_name

    and to specify dark matter only, we would use

    $ gsnap -t 010000 snapshot_file_name

  • To compute the velocity dispersion of stars younger than T time units…


    $ gsnap -a T file_name
    where T > 0

  • To compute the velocity dispersion of stars older than T time units…


    $ gsnap -a T file_name
    where T < 0

  • To compute the velocity dispersion of stars between the ages of T_1 and T_2 time units…


    $ gsnap --age_bin T_1 T_2 file_name

  • To center velocity dispersion measurements on the first black hole listed in the snapshot file, rather than focusing on the center of mass of the system:


    $ gsnap -n file_name

    Since the black hole is typically in the nucleus of a galaxy, this is a nucleus-centered velocity dispersion.

Viewing

  • To view the snapshot along the z axis,


    $ gsnap --view -t ###### snapshot_file_name

    This creates an image file named snapshot_file_name.png. For example, to view all star particles in the simulation snapshot named snapshot_505 from the z-direction, we would use:

    $ gsnap --view p -t 001110 snapshot_505

    and the output file would be snapshot_505.png.

  • To preview the snapshot interactively (without saving the image to disk), use the --iview flag:


    $ gsnap --view i -t ###### snapshot_file_name

    Using this window, you can interactively rotate and zoom the snapshot visualization and change the scaling of the pixel brightness by changing the gamma value.

  • To create an image of the gas component using a volume rendering / ray casting scheme,


    $ gsnap --view gas file_name

The output will be an image named file_name.png

  • To create a volume rendering of the of the stellar component with no dust attenuation,

    $ gsnap --view flux file_name

    The output will be an image named file_name.png

  • To create a volume rendering of the of the stellar component with dust attenuation,


    $ gsnap --view flux -t 101110 file_name

    The output will be an image named file_name.png

Note: For all viewing options, you should probably use a parameter file because the default values are not likely what you will want to use.

Interpolation

  • To interpolate between the snapshots file_1 and file_2 to create N intermediate snapshots named inter.1, inter.2, inter.3,…, inter.N


    $ gsnap -i --frames N --beg file_1 --end file_2 --out inter

  • To create interpolated images rather than interpolated snapshots:


    $ gsnap -Ig --frames N --beg file_1 --end file_2 --out inter

    This will create volume renderings of the gas component named inter.1.png, inter.2.png, inter.3.png,…,inter.N.png

    $ gsnap -It 101110 --view flux --frames N --beg file_1 --end file_2 --out inter

    This will create volume renderings of the stellar component with dust extinction. As above, the images will be named inter.1.png, inter.2.png, inter.3.png,…,inter.N.png