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The MUSE Hubble Ultra Deep Field Survey
II. Spectroscopic redshifts and comparisons to color selections of high-redshift galaxies

H. Inami, R. Bacon, J. Brinchmann, J. Richard, T. Contini, S. Conseil, S. Hamer, M. Akhlaghi, N. F. Bouché, B. Clement, G. Desprez, A. Drake, T. Hashimoto, F. Leclercq, M. V. Maseda, L. Michel-Dansac, M. Paalvast, L. Tresse, E. Ventou, W. Kollatschny, L. A. Boogaard, H. Finley, R. A. Marino, J. Schaye, L. Wisotzki

Abstract
We have conducted a two-layered spectroscopic survey (1′ × 1′ ultra deep and 3′ × 3′ deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for Hubble Space Telescope (HST) continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond > 3 and to HST/F775W magnitudes as faint as ≈ 30 mag (AB, 1σ). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [O II] at z < 1.5 (473 objects) and Lyα at 2.9 < < 6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains ≳ 20% up to 28–29 mag and ≈ 27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ≈ 80% of the targeted z ~ 2.7 galaxies. However, for higher redshift selections (F435WF606W, and F775W dropouts), the success rates decrease to ≈ 20–40%. We empirically redefine the selection boundaries to make an attempt to improve them to ≈ 60%. The revised boundaries allow bluer colors that capture Lyα emitters with high Lyα equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.

Keywords
galaxies: high-redshift; galaxies: formation; galaxies: evolution; catalogs; surveys; Astrophysics - Astrophysics of Galaxies

Astronomy & Astrophysics
Volume 608, Article Number A2, Number of pages 26
2017 December

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia