pygedm.pygedm

Python API to YMW16, NE2001, and YT2020 Galactic electron density models

References

[1] Cordes, J. M., & Lazio, T. J. W. (2002), NE2001.I. A New Model for the Galactic Distribution of Free Electrons and its Fluctuations, arXiv e-prints, astro-ph/0207156.

[2] Cordes, J. M., & Lazio, T. J. W. (2003), NE2001. II. Using Radio Propagation Data to Construct a Model for the Galactic Distribution of Free Electrons, arXiv e-prints, astro-ph/0301598.

[3] Yao, J. M., Manchester, R. N., & Wang, N. (2017), A New Electron-density Model for Estimation of Pulsar and FRB Distances, ApJ, 835, 29.

[4] Yamasaki S, Totani T (2020), The Galactic Halo Contribution to the Dispersion Measure of Extragalactic Fast Radio Bursts The Astrophysical Journal, Volume 888, Issue 2, id.105

pygedm.pygedm.calculate_electron_density_lbr(gl, gb, dist, method='ymw16')

Calculate electron density at a point with Galactic coords (ga, gl) at given distance

Parameters:

gl (float, Angle, or Quantity) – Galatic longitude in degrees (or astropy Angle)
gb (float, Angle, or Quantity) – Galactic latitude in degrees (or astropy Angle)
dist (float or Quantity) – Distance in pc

Returns:

electron density in cm^-3

Return type:

N_e (astropy.Quantity)

pygedm.pygedm.calculate_electron_density_xyz(x, y, z, method='ymw16')

Calculate electron density at a point with galactocentric coords (x, y, z)

Parameters:

x (float or Quantity) – galactocentric X coordinate in pc
y (float or Quantity) – galactocentric Y coordinate in pc
z (float or Quantity) – galactocentric Z coordinate in pc

Returns:

electron density in cm^-3

Return type:

N_e (astropy.quantity)

pygedm.pygedm.calculate_halo_dm(gl, gb, method='yt2020', component='both')

Compute halo DM

Parameters:

gl (float, Angle, or Quantity) – Galatic latitude in degrees (or astropy Angle)
gb (float, Angle, or Quantity) – Galactic latitude in degrees (or astropy Angle)
method (str) – one of ‘yt2020’ (only YT2020 supported currently)
component (str) – Compute ‘spherical’ component of halo, ‘disk’, or ‘both’ components.

Returns:

Dispersion measure in (pc/cm3)

Return type:

DM (float)

pygedm.pygedm.convert_lbr_to_xyz(gl, gb, dist, method='ymw16')

Convert Galactic (l,b,r) coords to Galactocentric (x,y,z) coords

Parameters:

gl (float, Angle, or Quantity) – Galatic longitude in degrees (or astropy Angle)
gb (float, Angle, or Quantity) – Galactic latitude in degrees (or astropy Angle)
dist (float or Quantity) – Distance in pc
method (str) – one of ‘ymw16’, ‘ne2001’, or ‘astropy’

Returns:

Galactocentric X, Y, Z coordinates

Return type:

xyz (tuple)

Notes

For transform, the Sun is located at (x=0, y=R_sun, z=z_sun) YMW16 uses R_sun of 8300 pc and z_sun of 6.0 pc NE2001 uses R_sun of 8500 pc and z_sun of 0.0 pc Both of these do a basic spherical to cartesian conversion.

astropy does a much more complicated conversion, see https://astropy.readthedocs.io/en/latest/coordinates/galactocentric.html This is the ‘proper’ coordinate system, but note that it is NOT COMPATIBLE WITH NE2001 OR YMW16! (!SEE EXAMPLE OUTPUT BELOW!)

Example output:

pygedm.convert_lbr_to_xyz(0, 0, 0, method='ymw16')
(<Quantity 0. pc>, <Quantity 8300. pc>, <Quantity 6. pc>)

pygedm.convert_lbr_to_xyz(0, 0, 0, method='ne2001')
(<Quantity 0. pc>, <Quantity 8500. pc>, <Quantity 0. pc>)

pygedm.convert_lbr_to_xyz(0, 0, 0, method='astropy')
(<Quantity -8499.95711754 pc>, <Quantity 0. pc>, <Quantity 27. pc>)

pygedm.pygedm.dist_to_dm(gl, gb, dist, mode='gal', method='ymw16', nu=1.0)

Convert a distance to a DM

Parameters:

gl (float in deg or astropy.Angle) – galactic longitude
gb (float in deg or astropy.Angle) – galactic latitude
dist (float or astropy.Quantity) – distance to source (pc) or if in mode IGM use (Mpc)
method (str) – choose electron density model, either ‘ymw16’ or ‘ne2001’
mode (str) – Gal, MC, or IGM (for YMW16 only)
nu (float in GHz or astropy.Quantity) – observing frequency (GHz)

Returns:

Dispersion measure (pc / cm3), scattering timescale at 1 GHz (s)

Return type:

dm (astropy.Quantity), tau_sc (astropy.Quantity)

pygedm.pygedm.dm_to_dist(gl, gb, dm, dm_host=0, mode='gal', method='ymw16', nu=1.0)

Convert a DM to a distance

Parameters:

gl (float in deg or astropy.Angle) – galactic longitude
gb (float in deg or astropy.Angle) – galactic latitude
dm (float in pc/cm3 or astropy.Quantity) – dispersion measure (pc cm^-3)
method (str) – choose electron density model, either ‘ymw16’ or ‘ne2001’
mode (str) – Gal, MC, or IGM (for YMW16 only)
nu (float in GHz or astropy.Quantity) – observing frequency (GHz)

Returns:

Distance (pc), scattering timescale at 1 GHz (s)

Return type:

dist (astropy.Quantity), tau_sc (astropy.Quantity)

pygedm.pygedm.generate_healpix_dm_map(dist=1, nside=64, method='ymw16')

Generate an all-sky healpix map for a given distance.

Parameters:

dist (float or Quantity) – Distance to integrate EDM out to. 30 kpc will go to edge
nside (int) – The NSIDE parameter for the healpix map (power of 2, larger => higher resolution)
method (str) – one of ‘ymw16’, ‘ne2001’, ‘ne2025’, ‘yt2020’ or ‘yt2020_analytic’

Notes

This method takes a fair amount of time to run – tens of seconds for NSIDE=32. YT2020 method is even slower, consider using yt2020_analytic

Returns:: Healpix map as a numpy array (1D), which can be viewed using the healpy.mollview() method
Return type:: hmap (np.array)