linear_alignments

Compute the terms P_II and P_GI which go into intrinsic aligment calculations

File	intrinsic_alignments/la_model/linear_alignments_interface.py
Attribution	CosmoSIS team
	Donnacha Kirk
URL
Citations	MNRAS 424 3 1647 (2012)
	New J Phys 9 12 444 (2007)

Intrinsic alignment refers to the extent to which galaxies align in the sky, before any alignment induced by gravitational lensing. It is a systematic error contribution to cosmic shear measurements and is predicted here in the form of two power spectra, one for the alignments, P_II, and one for the alignment-shear correlations, P_GI.

In the original Linear Alignment model it was assumed that alignments among galaxies were laid down early in the evolution of structure, and then (on average) did not vary since. The amount of alignment on a given scale was then related to the linear power spectrum at that scale.

The P_II and P_GI power is described in terms of a power spectrum, integrated over with a Limber integral in a similar way to the shear power spectrum. This code does not do that integral, it just calculates P_II and P_GI.

A number of variations to the LA model have been discussed since, and this module implements three of them. The history is a little convoluted as an error was found in early work missing a factor of (1+z), so one of our models is a corrected version of one of the other ones. Our models are:

• Bridle & King

• Bridle & King (corrected)

• Kirk, Rassat, Host, Bridle

See these papers for details of these models.

Assumptions

• Uses one of three models for how matter power is turned into intrinsic alignments

Setup Parameters

Name	Type	Default	Description
method	str		Which model to run. Choice of ‘bk’, ‘bk_corrected’, ‘krhb’,
name	str		If set, save the outputs to sections with the name as a suffix, e.g intrinsic_power_NAME
grid_mode	bool	False	Whether to save the fields b(k,z) and r(k,z) as described in Bridle & King instead of applying directly to P(k)
do_galaxy_intrinsic	bool	False	Compute the matter-IA cross correlation.

Input values

Section	Name	Type	Default	Description
cosmological_parameters	omega_m	real		Density fraction of all matter.
intrinsic_alignment_parameters	A	real		Single parameter scaling power spectra
matter_power_nl	z	real 1d		redshift values of P(k,z) samples
	k_h	real 1d		k values of P(k,z) samples in units of Mpc/h
	P_k	real 2d		non-linear matter power spectrum at samples in (Mpc/h)^{-3}
matter_power_lin	z	real 1d		redshift values of P(k,z) samples
	k_h	real 1d		k values of P(k,z) samples in units of Mpc/h
	P_k	real 2d		linear matter power spectrum at samples in (Mpc/h)^{-3}
matter_galaxy_power	z	real 1d		redshift values of P(k,z) samples (if do_galaxy_intrinsic)
	k_h	real 1d		k values of P(k,z) samples in units of Mpc/h (if do_galaxy_intrinsic)
	P_k	real 2d		Nonlinear matter-galaxy cross power spectrum at samples in (Mpc/h)^{-3} (if do_galaxy_intrinsic)

Output values

Output values

Section	Name	Type	Description
intrinsic_power	z	real 1d	Redshift values of P(k,z) samples (if grid_mode=F, the default)
	k_h	real 1d	Wavenumber k values of P(k,z) samples in units of Mpc/h (if grid_mode=F, the default)
	P_k	real 2d	Spectrum of intrinsic-intrinsic power at samples in (Mpc/h)^{-3} (if grid_mode=F, the default)
matter_intrinsic_power	z	real 1d	Redshift values of P(k,z) samples (if grid_mode=F, the default)
	k_h	real 1d	; k values of P(k,z) samples in units of Mpc/h (if grid_mode=F, the default)
	P_k	real 2d	Spectrum of shear-intrinsic power at samples in (Mpc/h)^{-3} (if grid_mode=F, the default)
intrinsic_alignment_parameters	z	real 1d	Redshift values ofsamples (if grid_mode=F, the default)
	k_h	real 1d	Wavenumber k values of samples in units of Mpc/h (if grid_mode=F, the default)
	b_I	real 2d	The ‘bias’ term described in eqn 27 of Kirk, Rassat, Host Bridle. (if grid_mode=T)
	r_I	real 2d	The cross-correlation ‘bias’ term described in eqn 28 of Kirk, Rassat, Host Bridle. (if grid_mode=T)