Euclid preparation. XX. The Complete Calibration of the Color-Redshift Relation survey: LBT observations and data release

Euclid Collaboration; Saglia, R.; De Nicola, S.; Fabricius, M.; Guglielmo, V.; Snigula, J.; Zöller, R.; Bender, R.; Heidt, J.; Masters, D.; Stern, D.; Paltani, S.; Amara, A.; Auricchio, N.; Baldi, M.; Bodendorf, C.; Bonino, D.; Branchini, E.; Brescia, M.; Brinchmann, J.; Camera, S.; Capobianco, V.; Carbone, C.; Carretero, J.; Castellano, M.; Cavuoti, S.; Cledassou, R.; Congedo, G.; Conselice, C. J.; Conversi, L.; Copin, Y.; Corcione, L.; Courbin, F.; Cropper, M.; Da Silva, A.; Degaudenzi, H.; Douspis, M.; Dubath, F.; Duncan, C. A. J.; Dupac, X.; Dusini, S.; Farrens, S.; Frailis, M.; Franceschi, E.; Galeotta, S.; Garilli, B.; Gillard, W.; Gillis, B.; Giocoli, C.; Grazian, A.; Grupp, F.; Haugan, S. V. H.; Hoekstra, H.; Holmes, W.; Hormuth, F.; Hornstrup, A.; Jahnke, K.; Kümmel, M.; Kermiche, S.; Kiessling, A.; Kunz, M.; Kurki-Suonio, H.; Laureijs, R.; Ligori, S.; Lilje, P. B.; Lloro, I.; Maiorano, E.; Marggraf, O.; Markovic, K.; Marulli, F.; Massey, R.; McCracken, H. J.; Melchior, M.; Meylan, G.; Moresco, M.; Moscardini, L.; Munari, E.; Niemi, S. M.; Padilla, C.; Pasian, F.; Pedersen, K.; Percival, W. J.; Pettorino, V.; Pires, S.; Poncet, M.; Popa, L.; Pozzetti, L.; Raison, F.; Renzi, A.; Rhodes, J.; Riccio, G.; Romelli, E.; Rossetti, E.; Sapone, D.; Sartoris, B.; Schneider, P.; Secroun, A.; Seidel, G.; Sirignano, C.; Sirri, G. et al.
Bibliographical reference

Astronomy and Astrophysics

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The Complete Calibration of the Color-Redshift Relation survey (C3R2) is a spectroscopic program designed to empirically calibrate the galaxy color-redshift relation to the Euclid depth (IE = 24.5), a key ingredient for the success of Stage IV dark energy projects based on weak lensing cosmology. A spectroscopic calibration sample that is as representative as possible of the galaxies in the Euclid weak lensing sample is being collected, selecting galaxies from a self-organizing map (SOM) representation of the galaxy color space. Here, we present the results of a near-infrared H- and K-band spectroscopic campaign carried out using the LUCI instruments at the LBT. For a total of 251 galaxies, we present new highly reliable redshifts in the 1.3 ≤ z ≤ 1.7 and 2 ≤ z ≤ 2.7 ranges. The newly-determined redshifts populate 49 SOM cells that previously contained no spectroscopic measurements and almost twice the occupation numbers of an additional 153 SOM cells. A final optical ground-based observational effort is needed to calibrate the missing cells, in particular in the redshift range 1.7 ≤ z ≤ 2.7, which lack spectroscopic calibration. In the end, Euclid itself will deliver telluric-free near-IR spectra that can complete the calibration.

The LBT is an international collaboration among institutions in the United States, Italy, and Germany. The LBT Corporation partners are: LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.