load_nz_fits module

Load a number density n(z) from a FITS file

Name: load_nz_fits

File: cosmosis-standard-library/number_density/load_nz_fits/load_nz_fits.py

Version: 1

Author(s):

CosmoSIS Team

URL:

Cite:

Rules:

If you use a file from a particular survey you should cite that survey

Assumptions:

Data is provided in FITS extensions NZ_{NAME}
There are various subtleties to do with the sampling and form of the n(z) data

Explanation

This module is designed to work with the number density part of the FITS
files described in:
http://github.com/joezuntz/2point/

High-precision analyses of two-point measurements require knowing precisely what
is meant by a given n(z) analysis. Most of the CosmoSIS standard library modules
downstream of this one assume that the n(z) specifies sample points in a smooth
curve, since that seems most physical. Most photo-z codes, on the other hand,
provide data in the form of histograms, with small bins in z having a constant
assumed n(z) within them.

The actual difference between these two forms is
usually well within the systematic errors associated with photometric
redshift estimation, so if you're doing a realistic analysis the difference should
be washed out. But for code comparison exercises where you are trying to ensure
0.1% level differences they are very large.

The parameter 'upsampling' in this module is designed to address this. Higher upsampling
values add new sample points in between the existing ones, so that the two forms
look much closer.

A proper solution to this, where we use splines the parts of the code that actually
use the n(z) that understand the histogram form, is in our roadmap.

##Parameters

These parameters can be set in the module's section in the ini parameter file.
If no default is specified then the parameter is required.

Parameter	Description
nz_file	String; absolute or relative path to an n(z) file
data_sets	String, space separated names of the extensions from the FITS files to load and save to the block
prefix_extension	Bool, default=T. Add the prefix NZ_ to the names in data_sets when looking in the FITS file
prefix_section	Bool, default=T. Add the same NZ_ prefix to the section names used in the block.
upsampling	Integer, default=1. The number of sample points output for each one in the file. n(z) is assumed flat between them. See notes above.

##Inputs

These parameters and data are inputs to the module, either supplied as parameters by the sampler or computed by some previous module. They are loaded from the data block.

Section	Parameter	Description

##Outputs

These parameters and data are computed as outputs from the module

Section	Parameter	Description
wl_number_density	nz	Integer; number of redshift samples
	nbin	Integer; number of bins
	z	Real vector; redshift sample values
	bin_	Real vector; n(z) at redshift sample values. bin_1, bin_2, ...

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cosmosis / default_modules / load_nz_fits_1

load_nz_fits module

Load a number density n(z) from a FITS file