Removing Imaging Systematics from Galaxy Clustering Measurements with Obiwan : Application to the SDSS-IV extended Baryon Oscillation Spectroscopic Survey Emission Line Galaxy Sample

TL;DR

This paper introduces Obiwan, a simulation-based tool that models imaging systematics in galaxy surveys to improve the accuracy of large-scale structure measurements, validated on SDSS-IV eBOSS ELG data.

Contribution

Obiwan is a novel forward-modeling tool that simulates the galaxy detection process to identify and correct imaging systematics in galaxy clustering analyses.

Findings

Systematic biases in imaging data are effectively identified and removed.

Clustering results using Obiwan are consistent with traditional map-based methods.

Validation on SDSS-IV eBOSS ELG sample confirms the reliability of the approach.

Abstract

This work presents the application of a new tool, Obiwan , which uses image simulations to determine the selection function of a galaxy redshift survey and calculate 3-dimensional (3D) clustering statistics. This is a forward model of the process by which images of the night sky are transformed into a 3D large--scale structure catalog. The photometric pipeline automatically detects and models galaxies and then generates a catalog of such galaxies with detailed information for each one of them, including their location, redshift and so on. Systematic biases in the imaging data are therefore imparted into the catalogs and must be accounted for in any scientific analysis of their information content. Obiwan simulates this process for samples selected from the Legacy Surveys imaging data. This imaging data will be used to select target samples for the next-generation Dark Energy Spectroscopic Instrument (DESI) experiment. Here, we apply Obiwan to a portion of the SDSS-IV extend Baryon Oscillation Spectroscopic Survey Emission Line Galaxies (ELG) sample. Systematic biases in the data are clearly identified and removed. We compare the 3D clustering results to those obtained by the map--based approach applied to the full eBOSS sample. We find the results are consistent, thereby validating the eBOSS ELG catalogs, presented in Raichoor(2020), used to obtain cosmological results.