pidgey 1.0.0

Description:

pidgey 1.0.0

pidgey







A python interface for dynamics of galaxies, using existing galactic dynamics libraries in Python (galpy, gala and agama) as backends.
This is currently used in the commensurability library.
Table of Contents

Installation
Usage

With agama
With gala
With galpy



Installation
Install this package via pip:
python -m pip install pidgey

Usage
Get the points from an orbit integration stored in an astropy.coordinates.SkyCoord object by calling the compute_orbit method of a backend. The backend can generally be obtained from the potential used for the orbit integration with the get_backend_from function.
import astropy.coordinates as c
import astropy.units as u

from pidgey import get_backend_from

def calculate_orbit(ic: c.SkyCoord,
potential: Any
) -> c.SkyCoord:
backend = get_backend_from(potential)
orbit = backend.compute_orbit(ic, potential, dt=0.01 * u.Gyr, steps=1000)
return orbit

With agama
import agama

bar_par = dict(
type="Ferrers",
mass=1e9,
scaleRadius=1.0,
axisRatioY=0.5,
axisratioz=0.4,
cutoffStrength=2.0,
patternSpeed=30,
)
disk_par = dict(type="Disk", mass=5e10, scaleRadius=3, scaleHeight=0.4)
bulge_par = dict(type="Sersic", mass=1e10, scaleRadius=1, axisRatioZ=0.6)
halo_par = dict(type="NFW", mass=1e12, scaleRadius=20, axisRatioZ=0.8)
potgal = agama.Potential(disk_par, bulge_par, halo_par, bar_par)

ic = c.SkyCoord(
x=6 * u.kpc,
y=0 * u.kpc,
z=2 * u.kpc,
v_x=0 * u.km / u.s,
v_y=150 * u.km / u.s,
v_z=0 * u.km / u.s,
frame="galactocentric",
representation_type="cartesian",
)
orbit = calculate_orbit(ic, potential)

With gala
import gala.potential as gp
from gala.units import galactic

disk = gp.MiyamotoNagaiPotential(m=6e10 * u.Msun, a=3.5 * u.kpc, b=280 * u.pc, units=galactic)
halo = gp.NFWPotential(m=6e11 * u.Msun, r_s=20.0 * u.kpc, units=galactic)
bar = gp.LongMuraliBarPotential(
m=1e10 * u.Msun,
a=4 * u.kpc,
b=0.8 * u.kpc,
c=0.25 * u.kpc,
alpha=25 * u.degree,
units=galactic,
)
pot = gp.CCompositePotential()
pot["disk"] = disk
pot["halo"] = halo
pot["bar"] = bar

frame = gp.ConstantRotatingFrame(Omega=[0, 0, 30] * u.km / u.s / u.kpc, units=galactic)
hamiltonian = gp.Hamiltonian(pot, frame=frame)
# this hamiltonian is pidgey's "potential"
# since it has an orbit integration method

ic = c.SkyCoord(
x=6 * u.kpc,
y=0 * u.kpc,
z=2 * u.kpc,
v_x=0 * u.km / u.s,
v_y=150 * u.km / u.s,
v_z=0 * u.km / u.s,
frame="galactocentric",
representation_type="cartesian",
)
orbit = calculate_orbit(ic, hamiltonian)

With galpy
import galpy.potential as gp

omega = 30 * u.km / u.s / u.kpc
halo = gp.NFWPotential(conc=10, mvir=1)
disc = gp.MiyamotoNagaiPotential(amp=5e10 * u.solMass, a=3 * u.kpc, b=0.1 * u.kpc)
bar = gp.SoftenedNeedleBarPotential(
amp=1e9 * u.solMass, a=1.5 * u.kpc, b=0 * u.kpc, c=0.5 * u.kpc, omegab=omega
)
potential = [halo, disc, bar]

ic = c.SkyCoord(
x=6 * u.kpc,
y=0 * u.kpc,
z=2 * u.kpc,
v_x=0 * u.km / u.s,
v_y=150 * u.km / u.s,
v_z=0 * u.km / u.s,
frame="galactocentric",
representation_type="cartesian",
)
orbit = calculate_orbit(ic, potential)