Loading Files

Alright, let’s start with some basics. Before we do anything, we will need to load a snapshot. You can do this using the load_sample convenience function. yt will autodetect that you want a tipsy snapshot and download it from the yt hub.

import yt

We will be looking at a fairly low resolution dataset.

This dataset is available for download at https://yt-project.org/data/TipsyGalaxy.tar.gz (10 MB).

ds = yt.load_sample("TipsyGalaxy")

We now have a TipsyDataset object called ds. Let’s see what fields it has.

ds.field_list

[('DarkMatter', 'Coordinates'),
 ('DarkMatter', 'Epsilon'),
 ('DarkMatter', 'FeMassFrac'),
 ('DarkMatter', 'Mass'),
 ('DarkMatter', 'Phi'),
 ('DarkMatter', 'Velocities'),
 ('Gas', 'Coordinates'),
 ('Gas', 'Density'),
 ('Gas', 'Epsilon'),
 ('Gas', 'FeMassFrac'),
 ('Gas', 'Mass'),
 ('Gas', 'Metals'),
 ('Gas', 'Phi'),
 ('Gas', 'Temperature'),
 ('Gas', 'Velocities'),
 ('Gas', 'smoothing_length'),
 ('Stars', 'Coordinates'),
 ('Stars', 'Epsilon'),
 ('Stars', 'FeMassFrac'),
 ('Stars', 'FormationTime'),
 ('Stars', 'Mass'),
 ('Stars', 'Metals'),
 ('Stars', 'Phi'),
 ('Stars', 'Velocities'),
 ('all', 'Coordinates'),
 ('all', 'Epsilon'),
 ('all', 'FeMassFrac'),
 ('all', 'Mass'),
 ('all', 'Phi'),
 ('all', 'Velocities'),
 ('nbody', 'Coordinates'),
 ('nbody', 'Epsilon'),
 ('nbody', 'FeMassFrac'),
 ('nbody', 'Mass'),
 ('nbody', 'Phi'),
 ('nbody', 'Velocities')]

yt also defines so-called “derived” fields. These fields are functions of the on-disk fields that live in the field_list. There is a derived_field_list attribute attached to the Dataset object - let’s take look at the derived fields in this dataset:

ds.derived_field_list

[('DarkMatter', 'Coordinates'),
 ('DarkMatter', 'Epsilon'),
 ('DarkMatter', 'FeMassFrac'),
 ('DarkMatter', 'Fe_fraction'),
 ('DarkMatter', 'Mass'),
 ('DarkMatter', 'Phi'),
 ('DarkMatter', 'Velocities'),
 ('DarkMatter', 'particle_angular_momentum'),
 ('DarkMatter', 'particle_angular_momentum_magnitude'),
 ('DarkMatter', 'particle_angular_momentum_x'),
 ('DarkMatter', 'particle_angular_momentum_y'),
 ('DarkMatter', 'particle_angular_momentum_z'),
 ('DarkMatter', 'particle_mass'),
 ('DarkMatter', 'particle_ones'),
 ('DarkMatter', 'particle_position'),
 ('DarkMatter', 'particle_position_cylindrical_radius'),
 ('DarkMatter', 'particle_position_cylindrical_theta'),
 ('DarkMatter', 'particle_position_cylindrical_z'),
 ('DarkMatter', 'particle_position_relative_x'),
 ('DarkMatter', 'particle_position_relative_y'),
 ('DarkMatter', 'particle_position_relative_z'),
 ('DarkMatter', 'particle_position_spherical_phi'),
 ('DarkMatter', 'particle_position_spherical_radius'),
 ('DarkMatter', 'particle_position_spherical_theta'),
 ('DarkMatter', 'particle_position_x'),
 ('DarkMatter', 'particle_position_y'),
 ('DarkMatter', 'particle_position_z'),
 ('DarkMatter', 'particle_radial_velocity'),
 ('DarkMatter', 'particle_radius'),
 ('DarkMatter', 'particle_specific_angular_momentum'),
 ('DarkMatter', 'particle_specific_angular_momentum_x'),
 ('DarkMatter', 'particle_specific_angular_momentum_y'),
 ('DarkMatter', 'particle_specific_angular_momentum_z'),
 ('DarkMatter', 'particle_velocity'),
 ('DarkMatter', 'particle_velocity_cylindrical_radius'),
 ('DarkMatter', 'particle_velocity_cylindrical_theta'),
 ('DarkMatter', 'particle_velocity_cylindrical_z'),
 ('DarkMatter', 'particle_velocity_magnitude'),
 ('DarkMatter', 'particle_velocity_relative_x'),
 ('DarkMatter', 'particle_velocity_relative_y'),
 ('DarkMatter', 'particle_velocity_relative_z'),
 ('DarkMatter', 'particle_velocity_spherical_phi'),
 ('DarkMatter', 'particle_velocity_spherical_radius'),
 ('DarkMatter', 'particle_velocity_spherical_theta'),
 ('DarkMatter', 'particle_velocity_x'),
 ('DarkMatter', 'particle_velocity_y'),
 ('DarkMatter', 'particle_velocity_z'),
 ('DarkMatter', 'relative_particle_position'),
 ('DarkMatter', 'relative_particle_position_x'),
 ('DarkMatter', 'relative_particle_position_y'),
 ('DarkMatter', 'relative_particle_position_z'),
 ('DarkMatter', 'relative_particle_velocity'),
 ('DarkMatter', 'relative_particle_velocity_x'),
 ('DarkMatter', 'relative_particle_velocity_y'),
 ('DarkMatter', 'relative_particle_velocity_z'),
 ('Gas', 'Coordinates'),
 ('Gas', 'Density'),
 ('Gas', 'Epsilon'),
 ('Gas', 'FeMassFrac'),
 ('Gas', 'Fe_fraction'),
 ('Gas', 'Mass'),
 ('Gas', 'Metals'),
 ('Gas', 'Phi'),
 ('Gas', 'Temperature'),
 ('Gas', 'Velocities'),
 ('Gas', 'angular_momentum'),
 ('Gas', 'angular_momentum_magnitude'),
 ('Gas', 'angular_momentum_x'),
 ('Gas', 'angular_momentum_y'),
 ('Gas', 'angular_momentum_z'),
 ('Gas', 'cylindrical_radius'),
 ('Gas', 'cylindrical_theta'),
 ('Gas', 'cylindrical_z'),
 ('Gas', 'density'),
 ('Gas', 'mass'),
 ('Gas', 'metallicity'),
 ('Gas', 'ones'),
 ('Gas', 'particle_angular_momentum'),
 ('Gas', 'particle_angular_momentum_magnitude'),
 ('Gas', 'particle_angular_momentum_x'),
 ('Gas', 'particle_angular_momentum_y'),
 ('Gas', 'particle_angular_momentum_z'),
 ('Gas', 'particle_mass'),
 ('Gas', 'particle_ones'),
 ('Gas', 'particle_position'),
 ('Gas', 'particle_position_cylindrical_radius'),
 ('Gas', 'particle_position_cylindrical_theta'),
 ('Gas', 'particle_position_cylindrical_z'),
 ('Gas', 'particle_position_relative_x'),
 ('Gas', 'particle_position_relative_y'),
 ('Gas', 'particle_position_relative_z'),
 ('Gas', 'particle_position_spherical_phi'),
 ('Gas', 'particle_position_spherical_radius'),
 ('Gas', 'particle_position_spherical_theta'),
 ('Gas', 'particle_position_x'),
 ('Gas', 'particle_position_y'),
 ('Gas', 'particle_position_z'),
 ('Gas', 'particle_radial_velocity'),
 ('Gas', 'particle_radius'),
 ('Gas', 'particle_specific_angular_momentum'),
 ('Gas', 'particle_specific_angular_momentum_x'),
 ('Gas', 'particle_specific_angular_momentum_y'),
 ('Gas', 'particle_specific_angular_momentum_z'),
 ('Gas', 'particle_velocity'),
 ('Gas', 'particle_velocity_cylindrical_radius'),
 ('Gas', 'particle_velocity_cylindrical_theta'),
 ('Gas', 'particle_velocity_cylindrical_z'),
 ('Gas', 'particle_velocity_magnitude'),
 ('Gas', 'particle_velocity_relative_x'),
 ('Gas', 'particle_velocity_relative_y'),
 ('Gas', 'particle_velocity_relative_z'),
 ('Gas', 'particle_velocity_spherical_phi'),
 ('Gas', 'particle_velocity_spherical_radius'),
 ('Gas', 'particle_velocity_spherical_theta'),
 ('Gas', 'particle_velocity_x'),
 ('Gas', 'particle_velocity_y'),
 ('Gas', 'particle_velocity_z'),
 ('Gas', 'position'),
 ('Gas', 'radial_velocity'),
 ('Gas', 'radius'),
 ('Gas', 'relative_particle_position'),
 ('Gas', 'relative_particle_position_x'),
 ('Gas', 'relative_particle_position_y'),
 ('Gas', 'relative_particle_position_z'),
 ('Gas', 'relative_particle_velocity'),
 ('Gas', 'relative_particle_velocity_x'),
 ('Gas', 'relative_particle_velocity_y'),
 ('Gas', 'relative_particle_velocity_z'),
 ('Gas', 'relative_x'),
 ('Gas', 'relative_y'),
 ('Gas', 'relative_z'),
 ('Gas', 'smoothing_length'),
 ('Gas', 'specific_angular_momentum'),
 ('Gas', 'specific_angular_momentum_x'),
 ('Gas', 'specific_angular_momentum_y'),
 ('Gas', 'specific_angular_momentum_z'),
 ('Gas', 'spherical_phi'),
 ('Gas', 'spherical_radius'),
 ('Gas', 'spherical_theta'),
 ('Gas', 'temperature'),
 ('Gas', 'velocity'),
 ('Gas', 'velocity_cylindrical_radius'),
 ('Gas', 'velocity_cylindrical_theta'),
 ('Gas', 'velocity_cylindrical_z'),
 ('Gas', 'velocity_magnitude'),
 ('Gas', 'velocity_relative_x'),
 ('Gas', 'velocity_relative_y'),
 ('Gas', 'velocity_relative_z'),
 ('Gas', 'velocity_spherical_phi'),
 ('Gas', 'velocity_spherical_radius'),
 ('Gas', 'velocity_spherical_theta'),
 ('Gas', 'velocity_x'),
 ('Gas', 'velocity_y'),
 ('Gas', 'velocity_z'),
 ('Gas', 'x'),
 ('Gas', 'y'),
 ('Gas', 'z'),
 ('Stars', 'Coordinates'),
 ('Stars', 'Epsilon'),
 ('Stars', 'FeMassFrac'),
 ('Stars', 'Fe_fraction'),
 ('Stars', 'FormationTime'),
 ('Stars', 'Mass'),
 ('Stars', 'Metals'),
 ('Stars', 'Phi'),
 ('Stars', 'Velocities'),
 ('Stars', 'creation_time'),
 ('Stars', 'metallicity'),
 ('Stars', 'particle_angular_momentum'),
 ('Stars', 'particle_angular_momentum_magnitude'),
 ('Stars', 'particle_angular_momentum_x'),
 ('Stars', 'particle_angular_momentum_y'),
 ('Stars', 'particle_angular_momentum_z'),
 ('Stars', 'particle_mass'),
 ('Stars', 'particle_ones'),
 ('Stars', 'particle_position'),
 ('Stars', 'particle_position_cylindrical_radius'),
 ('Stars', 'particle_position_cylindrical_theta'),
 ('Stars', 'particle_position_cylindrical_z'),
 ('Stars', 'particle_position_relative_x'),
 ('Stars', 'particle_position_relative_y'),
 ('Stars', 'particle_position_relative_z'),
 ('Stars', 'particle_position_spherical_phi'),
 ('Stars', 'particle_position_spherical_radius'),
 ('Stars', 'particle_position_spherical_theta'),
 ('Stars', 'particle_position_x'),
 ('Stars', 'particle_position_y'),
 ('Stars', 'particle_position_z'),
 ('Stars', 'particle_radial_velocity'),
 ('Stars', 'particle_radius'),
 ('Stars', 'particle_specific_angular_momentum'),
 ('Stars', 'particle_specific_angular_momentum_x'),
 ('Stars', 'particle_specific_angular_momentum_y'),
 ('Stars', 'particle_specific_angular_momentum_z'),
 ('Stars', 'particle_velocity'),
 ('Stars', 'particle_velocity_cylindrical_radius'),
 ('Stars', 'particle_velocity_cylindrical_theta'),
 ('Stars', 'particle_velocity_cylindrical_z'),
 ('Stars', 'particle_velocity_magnitude'),
 ('Stars', 'particle_velocity_relative_x'),
 ('Stars', 'particle_velocity_relative_y'),
 ('Stars', 'particle_velocity_relative_z'),
 ('Stars', 'particle_velocity_spherical_phi'),
 ('Stars', 'particle_velocity_spherical_radius'),
 ('Stars', 'particle_velocity_spherical_theta'),
 ('Stars', 'particle_velocity_x'),
 ('Stars', 'particle_velocity_y'),
 ('Stars', 'particle_velocity_z'),
 ('Stars', 'relative_particle_position'),
 ('Stars', 'relative_particle_position_x'),
 ('Stars', 'relative_particle_position_y'),
 ('Stars', 'relative_particle_position_z'),
 ('Stars', 'relative_particle_velocity'),
 ('Stars', 'relative_particle_velocity_x'),
 ('Stars', 'relative_particle_velocity_y'),
 ('Stars', 'relative_particle_velocity_z'),
 ('all', 'Coordinates'),
 ('all', 'Epsilon'),
 ('all', 'FeMassFrac'),
 ('all', 'Fe_fraction'),
 ('all', 'Mass'),
 ('all', 'Phi'),
 ('all', 'Velocities'),
 ('all', 'particle_angular_momentum'),
 ('all', 'particle_angular_momentum_magnitude'),
 ('all', 'particle_angular_momentum_x'),
 ('all', 'particle_angular_momentum_y'),
 ('all', 'particle_angular_momentum_z'),
 ('all', 'particle_mass'),
 ('all', 'particle_ones'),
 ('all', 'particle_position'),
 ('all', 'particle_position_cylindrical_radius'),
 ('all', 'particle_position_cylindrical_theta'),
 ('all', 'particle_position_cylindrical_z'),
 ('all', 'particle_position_relative_x'),
 ('all', 'particle_position_relative_y'),
 ('all', 'particle_position_relative_z'),
 ('all', 'particle_position_spherical_phi'),
 ('all', 'particle_position_spherical_radius'),
 ('all', 'particle_position_spherical_theta'),
 ('all', 'particle_position_x'),
 ('all', 'particle_position_y'),
 ('all', 'particle_position_z'),
 ('all', 'particle_radial_velocity'),
 ('all', 'particle_radius'),
 ('all', 'particle_specific_angular_momentum'),
 ('all', 'particle_specific_angular_momentum_x'),
 ('all', 'particle_specific_angular_momentum_y'),
 ('all', 'particle_specific_angular_momentum_z'),
 ('all', 'particle_velocity'),
 ('all', 'particle_velocity_cylindrical_radius'),
 ('all', 'particle_velocity_cylindrical_theta'),
 ('all', 'particle_velocity_cylindrical_z'),
 ('all', 'particle_velocity_magnitude'),
 ('all', 'particle_velocity_relative_x'),
 ('all', 'particle_velocity_relative_y'),
 ('all', 'particle_velocity_relative_z'),
 ('all', 'particle_velocity_spherical_phi'),
 ('all', 'particle_velocity_spherical_radius'),
 ('all', 'particle_velocity_spherical_theta'),
 ('all', 'particle_velocity_x'),
 ('all', 'particle_velocity_y'),
 ('all', 'particle_velocity_z'),
 ('all', 'relative_particle_position'),
 ('all', 'relative_particle_position_x'),
 ('all', 'relative_particle_position_y'),
 ('all', 'relative_particle_position_z'),
 ('all', 'relative_particle_velocity'),
 ('all', 'relative_particle_velocity_x'),
 ('all', 'relative_particle_velocity_y'),
 ('all', 'relative_particle_velocity_z'),
 ('deposit', 'DarkMatter_cic'),
 ('deposit', 'DarkMatter_cic_velocity_x'),
 ('deposit', 'DarkMatter_cic_velocity_y'),
 ('deposit', 'DarkMatter_cic_velocity_z'),
 ('deposit', 'DarkMatter_count'),
 ('deposit', 'DarkMatter_density'),
 ('deposit', 'DarkMatter_mass'),
 ('deposit', 'DarkMatter_nn_velocity_x'),
 ('deposit', 'DarkMatter_nn_velocity_y'),
 ('deposit', 'DarkMatter_nn_velocity_z'),
 ('deposit', 'Gas_cic'),
 ('deposit', 'Gas_cic_velocity_x'),
 ('deposit', 'Gas_cic_velocity_y'),
 ('deposit', 'Gas_cic_velocity_z'),
 ('deposit', 'Gas_count'),
 ('deposit', 'Gas_density'),
 ('deposit', 'Gas_mass'),
 ('deposit', 'Gas_nn_velocity_x'),
 ('deposit', 'Gas_nn_velocity_y'),
 ('deposit', 'Gas_nn_velocity_z'),
 ('deposit', 'Stars_cic'),
 ('deposit', 'Stars_cic_velocity_x'),
 ('deposit', 'Stars_cic_velocity_y'),
 ('deposit', 'Stars_cic_velocity_z'),
 ('deposit', 'Stars_count'),
 ('deposit', 'Stars_density'),
 ('deposit', 'Stars_mass'),
 ('deposit', 'Stars_nn_velocity_x'),
 ('deposit', 'Stars_nn_velocity_y'),
 ('deposit', 'Stars_nn_velocity_z'),
 ('deposit', 'all_cic'),
 ('deposit', 'all_cic_velocity_x'),
 ('deposit', 'all_cic_velocity_y'),
 ('deposit', 'all_cic_velocity_z'),
 ('deposit', 'all_count'),
 ('deposit', 'all_density'),
 ('deposit', 'all_mass'),
 ('deposit', 'all_nn_velocity_x'),
 ('deposit', 'all_nn_velocity_y'),
 ('deposit', 'all_nn_velocity_z'),
 ('deposit', 'nbody_cic'),
 ('deposit', 'nbody_cic_velocity_x'),
 ('deposit', 'nbody_cic_velocity_y'),
 ('deposit', 'nbody_cic_velocity_z'),
 ('deposit', 'nbody_count'),
 ('deposit', 'nbody_density'),
 ('deposit', 'nbody_mass'),
 ('deposit', 'nbody_nn_velocity_x'),
 ('deposit', 'nbody_nn_velocity_y'),
 ('deposit', 'nbody_nn_velocity_z'),
 ('gas', 'Fe_fraction'),
 ('gas', 'angular_momentum'),
 ('gas', 'angular_momentum_magnitude'),
 ('gas', 'angular_momentum_x'),
 ('gas', 'angular_momentum_y'),
 ('gas', 'angular_momentum_z'),
 ('gas', 'cutting_plane_velocity_x'),
 ('gas', 'cutting_plane_velocity_y'),
 ('gas', 'cutting_plane_velocity_z'),
 ('gas', 'cylindrical_radius'),
 ('gas', 'cylindrical_theta'),
 ('gas', 'cylindrical_z'),
 ('gas', 'density'),
 ('gas', 'dynamical_time'),
 ('gas', 'four_velocity_magnitude'),
 ('gas', 'four_velocity_t'),
 ('gas', 'four_velocity_x'),
 ('gas', 'four_velocity_y'),
 ('gas', 'four_velocity_z'),
 ('gas', 'jeans_mass'),
 ('gas', 'kT'),
 ('gas', 'kinetic_energy_density'),
 ('gas', 'lorentz_factor'),
 ('gas', 'mass'),
 ('gas', 'mean_molecular_weight'),
 ('gas', 'metal_mass'),
 ('gas', 'metallicity'),
 ('gas', 'momentum_density_x'),
 ('gas', 'momentum_density_y'),
 ('gas', 'momentum_density_z'),
 ('gas', 'momentum_x'),
 ('gas', 'momentum_y'),
 ('gas', 'momentum_z'),
 ('gas', 'number_density'),
 ('gas', 'ones'),
 ('gas', 'particle_mass'),
 ('gas', 'particle_position'),
 ('gas', 'particle_position_cylindrical_radius'),
 ('gas', 'particle_position_cylindrical_theta'),
 ('gas', 'particle_position_cylindrical_z'),
 ('gas', 'particle_position_relative_x'),
 ('gas', 'particle_position_relative_y'),
 ('gas', 'particle_position_relative_z'),
 ('gas', 'particle_position_spherical_phi'),
 ('gas', 'particle_position_spherical_radius'),
 ('gas', 'particle_position_spherical_theta'),
 ('gas', 'particle_position_x'),
 ('gas', 'particle_position_y'),
 ('gas', 'particle_position_z'),
 ('gas', 'position'),
 ('gas', 'radial_velocity'),
 ('gas', 'radial_velocity_absolute'),
 ('gas', 'radius'),
 ('gas', 'relative_velocity_x'),
 ('gas', 'relative_velocity_y'),
 ('gas', 'relative_velocity_z'),
 ('gas', 'relative_x'),
 ('gas', 'relative_y'),
 ('gas', 'relative_z'),
 ('gas', 'smoothing_length'),
 ('gas', 'specific_angular_momentum'),
 ('gas', 'specific_angular_momentum_magnitude'),
 ('gas', 'specific_angular_momentum_x'),
 ('gas', 'specific_angular_momentum_y'),
 ('gas', 'specific_angular_momentum_z'),
 ('gas', 'spherical_phi'),
 ('gas', 'spherical_radius'),
 ('gas', 'spherical_theta'),
 ('gas', 'tangential_over_velocity_magnitude'),
 ('gas', 'tangential_velocity'),
 ('gas', 'temperature'),
 ('gas', 'velocity'),
 ('gas', 'velocity_cylindrical_radius'),
 ('gas', 'velocity_cylindrical_theta'),
 ('gas', 'velocity_cylindrical_z'),
 ('gas', 'velocity_los'),
 ('gas', 'velocity_magnitude'),
 ('gas', 'velocity_relative_x'),
 ('gas', 'velocity_relative_y'),
 ('gas', 'velocity_relative_z'),
 ('gas', 'velocity_spherical_phi'),
 ('gas', 'velocity_spherical_radius'),
 ('gas', 'velocity_spherical_theta'),
 ('gas', 'velocity_x'),
 ('gas', 'velocity_y'),
 ('gas', 'velocity_z'),
 ('gas', 'x'),
 ('gas', 'y'),
 ('gas', 'z'),
 ('index', 'cell_volume'),
 ('index', 'cylindrical_radius'),
 ('index', 'cylindrical_theta'),
 ('index', 'cylindrical_z'),
 ('index', 'dx'),
 ('index', 'dy'),
 ('index', 'dz'),
 ('index', 'grid_indices'),
 ('index', 'grid_level'),
 ('index', 'morton_index'),
 ('index', 'ones'),
 ('index', 'ones_over_dx'),
 ('index', 'path_element_x'),
 ('index', 'path_element_y'),
 ('index', 'path_element_z'),
 ('index', 'radius'),
 ('index', 'spherical_phi'),
 ('index', 'spherical_radius'),
 ('index', 'spherical_theta'),
 ('index', 'virial_radius_fraction'),
 ('index', 'volume'),
 ('index', 'x'),
 ('index', 'y'),
 ('index', 'z'),
 ('index', 'zeros'),
 ('nbody', 'Coordinates'),
 ('nbody', 'Epsilon'),
 ('nbody', 'FeMassFrac'),
 ('nbody', 'Fe_fraction'),
 ('nbody', 'Mass'),
 ('nbody', 'Phi'),
 ('nbody', 'Velocities'),
 ('nbody', 'particle_angular_momentum'),
 ('nbody', 'particle_angular_momentum_magnitude'),
 ('nbody', 'particle_angular_momentum_x'),
 ('nbody', 'particle_angular_momentum_y'),
 ('nbody', 'particle_angular_momentum_z'),
 ('nbody', 'particle_mass'),
 ('nbody', 'particle_ones'),
 ('nbody', 'particle_position'),
 ('nbody', 'particle_position_cylindrical_radius'),
 ('nbody', 'particle_position_cylindrical_theta'),
 ('nbody', 'particle_position_cylindrical_z'),
 ('nbody', 'particle_position_relative_x'),
 ('nbody', 'particle_position_relative_y'),
 ('nbody', 'particle_position_relative_z'),
 ('nbody', 'particle_position_spherical_phi'),
 ('nbody', 'particle_position_spherical_radius'),
 ('nbody', 'particle_position_spherical_theta'),
 ('nbody', 'particle_position_x'),
 ('nbody', 'particle_position_y'),
 ('nbody', 'particle_position_z'),
 ('nbody', 'particle_radial_velocity'),
 ('nbody', 'particle_radius'),
 ('nbody', 'particle_specific_angular_momentum'),
 ('nbody', 'particle_specific_angular_momentum_x'),
 ('nbody', 'particle_specific_angular_momentum_y'),
 ('nbody', 'particle_specific_angular_momentum_z'),
 ('nbody', 'particle_velocity'),
 ('nbody', 'particle_velocity_cylindrical_radius'),
 ('nbody', 'particle_velocity_cylindrical_theta'),
 ('nbody', 'particle_velocity_cylindrical_z'),
 ('nbody', 'particle_velocity_magnitude'),
 ('nbody', 'particle_velocity_relative_x'),
 ('nbody', 'particle_velocity_relative_y'),
 ('nbody', 'particle_velocity_relative_z'),
 ('nbody', 'particle_velocity_spherical_phi'),
 ('nbody', 'particle_velocity_spherical_radius'),
 ('nbody', 'particle_velocity_spherical_theta'),
 ('nbody', 'particle_velocity_x'),
 ('nbody', 'particle_velocity_y'),
 ('nbody', 'particle_velocity_z'),
 ('nbody', 'relative_particle_position'),
 ('nbody', 'relative_particle_position_x'),
 ('nbody', 'relative_particle_position_y'),
 ('nbody', 'relative_particle_position_z'),
 ('nbody', 'relative_particle_velocity'),
 ('nbody', 'relative_particle_velocity_x'),
 ('nbody', 'relative_particle_velocity_y'),
 ('nbody', 'relative_particle_velocity_z')]

All of the field in the field_list are arrays containing the values for the associated particles. These haven’t been smoothed or gridded in any way. We can grab the array-data for these particles using ds.all_data(). For example, let’s take a look at a temperature-colored scatterplot of the gas particles in this output.

%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np

ad = ds.all_data()
xcoord = ad["Gas", "Coordinates"][:, 0].v
ycoord = ad["Gas", "Coordinates"][:, 1].v
logT = np.log10(ad["Gas", "Temperature"])
plt.scatter(
    xcoord, ycoord, c=logT, s=2 * logT, marker="o", edgecolor="none", vmin=2, vmax=6
)
plt.xlim(-20, 20)
plt.ylim(-20, 20)
cb = plt.colorbar()
cb.set_label(r"$\log_{10}$ Temperature")
plt.gcf().set_size_inches(15, 10)

Making Smoothed Images

yt will automatically generate smoothed versions of these fields that you can use to plot. Let’s make a temperature slice and a density projection.

yt.SlicePlot(ds, "z", ("gas", "density"), width=(40, "kpc"), center="m")

yt.ProjectionPlot(ds, "z", ("gas", "density"), width=(40, "kpc"), center="m")

Not only are the values in the tipsy snapshot read and automatically smoothed, the auxiliary files that have physical significance are also smoothed. Let’s look at a slice of Iron mass fraction.

yt.SlicePlot(ds, "z", ("gas", "Fe_fraction"), width=(40, "kpc"), center="m")