Radio Weak Lensing measurement in the Visibility Domain
This is a complete version of RadioLensfit.
Three tools are provided.
1. Catalog
Simulation of a real galaxy catalog ordered by flux within a given field of view (arcmin). According to the related distributions (see papers), it randomly generates: position l,m (RAD) in a disk area flux (uJy) FWHM/scalelength (arcsec), ellipticity components e1, e2
Distribution parameters can be modified changing the default_params.h
Usage: Catalog (number of sources) (effective field of view) (minimum flux) Output: text file where each line corresponds to a SF galaxy.
2. Simulate
Simulation of a radio weak lensing observation with a given reduced cosmic shear and a given source catalog of SF galaxies. The source catalog is a text file containing for each source (row) l,m position (rad), flux (uJy), fwhm/scalelength (arcsec), ellipticity components e1,e2. Source can be modelled either according to the Gaussian profile or Exponential profile (Sersic index 1). Radio telescope configuration must be provided in a Measurement Set. The effect of the input reduced cosmic shear is applied to galaxies ellipticity. The instrumental gaussian noise variance is computed based on the antenna SEFD of the radiotelescope and time and frequency sampling interval. Signal-to-noise (SNR) is also computed. The corresponding simulated visibilities observed by the radio telescope are written in the DATA column of the same Measurement Set (I stokes component). The input catalog is updated with the SNR values, the new file hathe same namewith "_SNR" added at the end.
Usage: Simulate (filename MS) (source catalog filename) (number of sources) (shear coord_1) (shear coord_2)
MPI version is also available.
3. RadioLensfit2
Measurement of star forming galaxy ellipticies from a radio weak lensing observation. Data visibilities and observation configuration must be provided in a Measurement Set (MS). If the MS contains 4 polarizations, I stokes is computed from them, otherwise a single polarization is expected to contain I stokes. The number of galaxies and the corresponding source catalog (ordered by decreasing flux or SNR) containing at least source SNR, position and flux must be provided (size is optional but highly recommended). Source position and flux (and scale factor) are used for source visibilities extraction, then shape measurement is performed according to RadioLensfit methodology: a single model fitting approach where the likelihood is marginalised over position, flux and scalelength source parameters. The list of galaxies with the measured ellipticities is written in a text file called "ellipticities_(nprocs)IF-(Nchannels)ch.txt".
Serial version usage: RadioLensfit2 (source catalog filename) (number of sources) (filename MS)
MPI version usage: RadioLensfit2-mpi (source catalog filename) (number of sources) (filename MSs prefix)
Before running the code:
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For the MPI versions, the MS must be split in individual spectral windows. All MSs must have the same name ending with the number of the spectral window and extension ".ms". Filename prefix consists in the common part of all the MS name, i.e. (without the final number and extension).
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Check/change default parameters (prior distributions, faceting, ....) in the default_params.h file.
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Default PSF weighting scheme is uniform. But other user weighting scheme functions can be defined and used in the gridding phase (file: evaluate_uv_grid.c), e.g. a tukey_tapering function is implemented (file: tukey_tapering.c).
Requirements:
- CASACORE library for Measurement Set I/O
- GSL library
- MPI library (for the parallel version)
Edit the Makefile:
- enable/disable OpenMP (default: enabled)
- enable/disable MPI (default: enabled)
- enable/disable FACET (default: enabled, mandatory if MPI is enabled)
- default source shape model is exponential, other models allowed are GAUSSIAN or MATCH_EXP (Galsim Exponential matched Gaussian FWHM)
- enable/disable reading of fwhm/scalelength from the galaxy catalog (default: SCALELENGTH_ON)
- update CASACORE include and library path
- set the compiler and compilation flags you want to use (default: GNU)
make all
If you use RadioLensfit2 and find it useful, please consider citing the related paper:
Rivi M., Miller L., RadioLensfit: an HPC Tool for Accurate Galaxy Shape Measurement with SKA, 2022, Astronomy & Computing,39,100574 - arXiv:2203.14071
Astrophysics Source Code Library ID ascl:2208.019 (https://ascl.net/2208.019.)