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BUG: Overgeneration of galaxies #578

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BUG: Overgeneration of galaxies #578

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5450d11
added h0 to number density
Sep 27, 2022
92921f7
Added galaxy fix
Nov 17, 2022
c17d772
Merge pull request #3 from skypyproject/main
Fox-Davidson Nov 17, 2022
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2 changes: 1 addition & 1 deletion skypy/galaxies/redshift.py
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Expand Up @@ -126,7 +126,7 @@ def f(lnx, a):
gam[i], _ = scipy.integrate.quad(f, lnxmin[i], np.inf, args=(alpha[i],))

# comoving number density is normalisation times upper incomplete gamma
density = phi_star*gam
density = phi_star*gam*np.power(cosmology.h, 3)

# sample redshifts from the comoving density
return redshifts_from_comoving_density(redshift=redshift, density=density,
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2 changes: 1 addition & 1 deletion skypy/galaxies/tests/test_redshift.py
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Expand Up @@ -32,7 +32,7 @@ def test_schechter_lf_redshift():
x_min = 10.**(-0.4*(M_lim - M_star))

# density with factor from upper incomplete gamma function
density = phi_star*gamma(alpha+1)*gammaincc(alpha+1, x_min)
density = phi_star*gamma(alpha+1)*gammaincc(alpha+1, x_min)*np.power(cosmo.h, 3)
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I don't think this is the right place to account for h. The parameter phi_star has the same dimension [unit] as the luminosity function, which is 1/V/luminosity [commonly Mpc^-3 mag^-1]. That means phi_star must agree with these dimensions/units.

In your example, you are using the parameters of Tortorelli2020. In this work, they are giving phi_star in units of h_70 = H_0/70. So the input parameter must be corrected by this unit. However, as your defined cosmology includes H_0 = 70, h_70 is equal to 1. Therefore, the number that you have in your config files corresponds to units of Mpc^-3 mag^-1, which are as I said the physical units.

If we, however, want to enable phi_star to be given in units of h_0, we would also need to specify this in the documentation. But in this case, the parameter in your config file has the wrong value.


# turn into galaxies/surface area
density *= (sky_area * cosmo.differential_comoving_volume(z)).to_value('Mpc3')
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