Abstract

Contributed Talk - Splinter 4MOST   (MW-0337)

4C3R2 in 4MOST Survey Verification (SPV): early lessons for Stage-IV redshift calibration

Luca Tortorelli, Daniel Gruen
LMU Munich

Redshift calibration remains one of the dominant observational systematics for Stage IV large scale structure cosmology. The 4MOST community survey 4C3R2 (4MOST Complete Calibration of the Colour Redshift Relation, Gruen+23) is designed to address this challenge by obtaining spectroscopic redshifts for a sample of galaxies that is representative of the colour space spanned by Stage IV photometric surveys, such as Euclid and Rubin-LSST. As project scientist, I will report on the current status of 4C3R2 with a focus on the 4MOST SPV phase, for which I serve as 4C3R2 responsible, describing the motivation behind our target selection and the process of nightly quality validation of SPV spectra for our survey science case. The lessons learned from this early dataset will inform what can be expected from the future of Stage IV redshift calibration with 4MOST, as the chosen SPV targets are among the hardest ones to get a redshift for. SPV data will also provide the unique opportunity to calibrate and improve the realism of our spectra simulator USpec (Tortorelli+26, public by the time of the meeting) and to perform controlled simulation-data comparisons by selecting mock SPV targets from our forward-modelling framework GaSBI-SPS (Tortorelli+25).