MultiBand_ImSim

A pipeline designed to generate multi-band images and create joint redshift-shear mock catalogues.

It contains 8 modules labelled as

• taskID 1: simulate images
• taskID 2: swarp images
• taskID 3: detect objects
• taskID 4: measure photometry
• taskID 5: estimate photo-z
• taskID 6_1: model PSF
• taskID 6_2: measure shapes
• taskID 7: create a combined catalogue

For usage instructions, run

`python modules/Run.py --help`

For sample test scripts, refer to the scripts directory.

Link to the input catalogues

• SURFS-based galaxies
• Trilegal stars

Link to the SKiLLS output catalogues

SKiLLS: SURFS-based KiDS-Legacy-Like Simulations

The post-processing codes can be found in the post_processing directory.

The catalogues can be download here

NOTE: These catalogues include all objects detected by SExtractor, encompassing false detections and stars. However, they also feature flag columns for applying KiDS-like photometry and lensfit selections. For more details, please refer to the readme.txt file within the shared folder.

AlphaRecal for lensfit measurements

The raw measurements from lensfit exhibit biases, primarily resulting from PSF anisotropy. We address these PSF-related distortions using an empirical approach, as elaborated in Section 4 of Li et al. (2023).

The relevant codes can be found in the alphaRecalPlus repository.

SDSS filters to KiDS/VIKING filters

After generating the images, we discovered that our SURFS-based galaxies possess photometry derived from SDSS filters, which differ slightly from the KiDS/VIKING filters. Consequently, we applied an empirical correction to the photometry measured from the simulated images to account for the filter discrepancies.

A comprehensive explanation is available in Appendix C of Li et al. (2023), and the pertinent codes can be found in the change_filters repository.

Shear calibration

Our shear calibration contains two main steps:

1. Estimate shear biases using constant shear image simulations, adhering to previous KiDS conventions, and apply data reweighting based on the lensfit-reported model signal-to-noise ratio and object resolution to accommodate potential discrepancies between simulations and data. Further information is provided in Section 5.1 of Li et al. (2023), with the associated codes located in the biasEstimation repository.

2. Refine the shear biases from constant shear image simulations to address high-order effects stemming from the 'shear-interplay' effect and PSF modeling uncertainties. Further information can be found in Sections 5.2 and 5.3 of Li et al. (2023), with the corresponding codes located in the correction_varShear_PSFmodelling repository.

Reference

Should the code or catalogues prove beneficial to your projects, please consider citing our paper: Li et al. 2023.