ryden04

skypy.galaxy.ellipticity.ryden04(mu_gamma, sigma_gamma, mu, sigma, size=None)

Ellipticity distribution of Ryden (2004).

The ellipticity is sampled by randomly projecting a 3D ellipsoid with principal axes \(A > B > C\) [1]. The distribution of the axis ratio \(\gamma = C/A\) is a truncated normal with mean \(\mu_\gamma\) and standard deviation \(\sigma_\gamma\). The distribution of \(\epsilon = \log(1 - B/A)\) is truncated normal with mean \(\mu\) and standard deviation \(\sigma\).

Parameters

mu_gammaarray_like

Mean of the truncated Gaussian for \(\gamma\).

sigma_gammaarray_like

Standard deviation for \(\gamma\).

muarray_like

Mean of the truncated Gaussian for \(\epsilon\).

sigmaarray_like

Standard deviation for \(\epsilon\).

sizeint or tuple of ints or None

Size of the sample. If None the size is inferred from the parameters.

References

1

Ryden B. S., 2004, ApJ, 601, 214

Examples

Sample 10000 random variates from the Ryden (2004) model with parameters \(\mu_\gamma = 0.222\), \(\sigma_\gamma = 0.056\), \(\mu = -1.85\), and \(\sigma = 0.89\).

>>> from skypy.galaxy.ellipticity import ryden04
>>> ellipticity = ryden04(0.222, 0.056, -1.85, 0.89, size=10000)