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import matplotlib.pyplot as plt
import yt
# Load the dataset.
ds = yt.load("IsolatedGalaxy/galaxy0030/galaxy0030")
# Create a sphere of radius 1 Mpc centered on the max density location.
sp = ds.sphere("max", (1, "Mpc"))
# Calculate and store the bulk velocity for the sphere.
bulk_velocity = sp.quantities.bulk_velocity()
sp.set_field_parameter("bulk_velocity", bulk_velocity)
# Create a 1D profile object for profiles over radius
# and add a velocity profile.
prof = yt.create_profile(
sp,
"radius",
("gas", "velocity_magnitude"),
units={"radius": "kpc"},
extrema={"radius": ((0.1, "kpc"), (1000.0, "kpc"))},
weight_field=("gas", "mass"),
)
# Create arrays to plot.
radius = prof.x
mean = prof["gas", "velocity_magnitude"]
std = prof.standard_deviation["gas", "velocity_magnitude"]
# Plot the average velocity magnitude.
plt.loglog(radius, mean, label="Mean")
# Plot the standard deviation of the velocity magnitude.
plt.loglog(radius, std, label="Standard Deviation")
plt.xlabel("r [kpc]")
plt.ylabel("v [cm/s]")
plt.legend()
plt.savefig("velocity_profiles.png")
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