photoz_distortion

Apply photometric redshift systematic biases to n(z) distributions

File	number_density/photoz_distortion/photoz_distortion.py
Attribution	CosmoSIS Team
URL

This module applies systematic biases to photometric redshift n(z) distributions to model the effects of photo-z estimation errors. It can apply three types of distortions:

1. Additive bias: Shift in mean redshift (delta_z offset)

2. Broadening: Increase in redshift scatter around the mean

3. Skewness: Asymmetric redistribution toward higher redshifts

The module can also add a population of catastrophic outliers using either a Gaussian ‘island’ or uniform distribution model. Biases can be applied globally or per-bin.

Assumptions

• Photo-z systematics can be modeled as shifts, broadening, and skewness

• Input n(z) distributions are well-sampled

Setup Parameters

Name	Type	Default	Description
mean	bool		Whether to apply additive bias (mean shift)
width	bool		Whether to apply broadening (width increase)
tail	bool		Whether to apply skewness (tail asymmetry)
bias_per_bin	bool		Whether biases are specified per bin or globally
sample	str		Name of the section containing n(z) to be modified
catastrophic_outliers	str		Model for catastrophic outliers (‘island’ or ‘uniform’)

Input values

Section	Name	Type	Default	Description
sample_section	nzbin	int		Number of redshift bins
	z	real 1d		Redshift sample values
	bin_{i}	real 1d		n(z) values for bin i to be modified
	bias_{i}	real		Additive bias for bin i (if mean=true and bias_per_bin=true)
	bias_1	real		Global additive bias (if mean=true and bias_per_bin=false)
	S_z_{i}	real		Broadening parameter for bin i (if width=true and bias_per_bin=true)
	S_z_1	real		Global broadening parameter (if width=true and bias_per_bin=false)
	T_z_{i}	real		Skewness parameter for bin i (if tail=true and bias_per_bin=true)
	T_z_1	real		Global skewness parameter (if tail=true and bias_per_bin=false)
	method	str		Catastrophic outlier method (‘island’ or ‘uniform’)
	fcat	real		Fraction of catastrophic outliers
	dzcat	real		Redshift range for catastrophic outliers
	zcat0	real		Central redshift for catastrophic outlier region
	zcat	real		Central redshift for catastrophic outlier distribution
	sigcat	real		Width of catastrophic outlier Gaussian (if method=’island’)

Output values

Output values

Section	Name	Type	Description
sample_section	z	real 1d	Extended redshift grid including padding
	bin_{i}	real 1d	Modified n(z) values for bin i with applied systematics