Module distance

Stellar galactic density function.

Galactic coordinate z: self-gravitating isothermal disk plus a Gaussian halo

See, e.g., Maiz-Apellaniz, Alfaro and Sota 2007/2008 (Poster)

Other values we found in the literature:

z_sun,hd,sigma,f = 24.7,34.2,1.62e-3,0.058

Parameters:

• z (array or float) - galactic coordinate z (parsec)
• z_sun (float) - Sun's distance above the Galactic plane (20.0 +/- 2.9 pc)
• hd (float) - disk scale height (31.8+/-1.6 pc)
• hh (float) - halo half width (490+/-170 pc)
• sigma (float) - number of stars per square parsec (total surface number density) (1.91e-3+/-0.11e-3)
• f (float) - fraction of stars in the halo population (0.039+/-0.015)

Returns: 3-tuple

halo+disk,halo and disk density function

Compute the probability for an object to be at distance r (pc), given its parallax (mas) and error on the parallax (mas) and a constant density function.

Unnormalised!

To obtain the probabilty, multiply with a stellar galactic density function.

Parameters:

• r (float/array) - distance (pc)
• plx (float/array) - parallax (mas)
• e_plx (float/array) - error on parallax (mas)

Returns:

probability function

Compute the probability for an object to be located at a distance r (pc), given its parallax and galactic lattitude.

theta in degrees plx is a tuple!

returns (unnormalised) probability density function.