ShearCo

Version 1.1 (07/2020) by Sandra Unruh
Second-order correlation functions with fast-Fourier transforms in C++

Table of contents

• General info
• Install and run
• Configuration file
• Features
• Status
• Acknowledgements
• Contact

General info

ShearCo is a C++-based code that calculates weak lensing two-point correlation functions efficiently. Currently, only shear-matter and convergence-matter correlation functions (galaxy-galaxy lensing signals) can be computed which will be expanded in the near future. It is suitable for large data sets and independent of the survey footprint. This code estimates and/or mitigates weak lensing magnification effects. A detailed account is given in the @PhD thesis (not published yet) and an abridged version can be found in the appendix of @Unruh2020.

Install and run

Dependencies:

• standard C compiler
• @FFTW3

Install:

• go to your desired directory (as of now, there is only one cd shear-matter-corr :P)
• compile with make

Run:

• run as ./bin/shearco
• option -c your_config_file lets you specify a configuration file
• option -k: for calculating the convergence-matter correlation function (or any ther scalar quantity)
• option -o: no output file is generated, the result will be displayed in the terminal
• option -q: shuts up all communication from the running code (including progress, warnings and errors) except missing config files

Input catalogs:

• the form should be [xpos ypos shear1 shear2 weight], where the shear is ignored for lens galaxies
• for source catalogs that contain the convergene [xpos ypos kappa 0 weight]
• the first line can but doesn't need to contain the number of objects (for long files it is recommended though)
• comment lines are allowed with the usual specifiers [#, %, /, //, !]

Output file:

• (header) weighted number of lenses and sources
• (1) linear mean radius in a bin
• (2) logarithmic mean radius in a bin
• (3) tangential shear / convergence
• (4) cross shear
• (5) contribution to tangential shear / convergence that comes from the large-scale structure
• (6) contribution to cross shear that comes from the large-scale structure

Testing the code:

• the folder test contains a lens and a source input catalog, the test config file and the test output file
• run with ./bin/shearco -c test/test_config and compare "tshear.ascii" and "test_tshear.ascii"
• the last two columns should not be identical since a random seed is used to calculate the contribution of the large-scale structure (lss)

Configuration file

The default file is "config". It has to contain the following entries. If you do not give a config file, the terminal will display a dialogue to build one. You can specify a config file using the -c option.

COMPULSORY
variable	type	example	description
input_lens_file	string	./test/cat_lens.ascii	lens galaxy catalogue in format [xpos ypos 0 0 weight]
input_source_file	string	./test/cat_source.ascii	source galaxy catalogue in format [xpos ypos shear1 shear2 weight]
theta_in	double	0.6	inner radius in input catalog units
theta_out	double	17	outer radius in input catalog units
N_annuli	integer	10	number of bins

OPTIONAL
variable	type	default	description
output_data_dir	string	./	output directory
N_pix	integer	4096	number of pixel N_pix^2 that the FFT uses (limits the precision)
bin_type	string	log	logarithmic or linear binning [lin, log]
units_input	string	?	units of xpos/ypos in the input catalog [arcsec, arcmin, deg, rad, Mpc, kpc, ?]
units_output	string	?	units for bins of the output [arcsec, arcmin, deg, rad, Mpc, kpc, ?]

IF angular input -> comoving output:
conv_R2theta	double	0.03	since the conversion from R to theta is cosmology dependent, the factor must be specified here

Features

• calculates the galaxy-shear correlation functions (galaxy-galaxy lensing signal)
• calculates galaxy-[any scalar quantity, like convergence, temperature, ...] correlation functions
• independent of the number of objects
• works with masks
• works on any survey footprint
• binning in angular or comoving coordinates

To-do list:

• magnification effects in galaxy-galaxy lensing (coding complete)
• implement convergence as an alternative to shear
• calculation of shear-shear correlations
• different input formats like .bin, .fits
• optimize to some simulations I already used (Millennium, SLICS)
• go beyond flat sky approximation

Status

Project is: in progress (motto is slowly but steady)
Last Update: July 2020

Acknowledgements

I thank Sven Heydenreich for thoroughly testing the code (aka bug hunting), Peter Schneider, Pierre Burger and Rongchuan Zhao for valuable discussions.

Contact

Created by @SandraUnruh -- feel free to contact me! I am grateful for all kinds of suggestion, criticism, bugs and encouragement as this project emerged from my PhD thesis and my experience is naturally limited.