DESI Complete Calibration of the Color-Redshift Relation (DC3R2)
Credit: D. Schlegel/Berkeley Lab using data from DESI

Disentangling galaxy evolution from galaxy distance requires us to catalog hundreds of thousands of galaxies spectroscopically as well as by color.

McCullough et al. 2024

Abstract

We present initial results from the Dark Energy Spectroscopic Instrument (DESI) Complete Calibration of the Color-Redshift Relation (DC3R2) secondary target survey. Our analysis uses 230k galaxies that overlap with KiDS-VIKING ugriZYHJKs photometry to calibrate the color-redshift relation and to inform photometric redshift (photo-z) inference methods of future weak lensing surveys. Together with Emission Line Galaxies (ELGs), Luminous Red Galaxies (LRGs), and the Bright Galaxy Survey (BGS) that provide samples of complementary color, the DC3R2 targets help DESI to span 56% of the color space visible to Euclid and LSST with high confidence spectroscopic redshifts. The effects of spectroscopic completeness and quality are explored, as well as systematic uncertainties introduced with the use of common Self Organizing Maps trained on different photometry than the analysis sample. We further examine the dependence of redshift on magnitude at fixed color, important for the use of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy sample. We find that noise in the KiDS-VIKING photometry introduces a dominant, apparent magnitude dependence of redshift at fixed color, which indicates a need for carefully chosen deep drilling fields, and survey simulation to model this effect for future weak lensing surveys.

Available data products

  • Read the paper: arxiv, MNRAS
  • The Astrobites overview, put together by Katherine Lee
  • The LMU press release, A Cosmic Wrestling Match, also available on Science Daily
  • To reproduce the figures in the paper, see the data and jupyter notebook available on Zenodo
  • For spectroscopy access: See DESI’s Early Data Release

    Data visualization widgets

    Explore the data set in your browser to understand how color, redshift, and SED type are related, alongside exposure times and the effects of bias on photometric redshift inference. Note that this runs best in full screen and may take a moment to load on first viewing.