Keck/MOSFIRE spectroscopic confirmation of a virgo-like cluster ancestor at z=2.095

Tiantian Yuan*, Themiya Nanayakkara, Glenn G. Kacprzak, Kim-Vy H. Tran, Karl Glazebrook, Lisa J. Kewley, Lee R. Spitler, Gregory B. Poole, Ivo Labbé, Caroline M. S. Straatman, Adam R. Tomczak

*Corresponding author for this work

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    We present spectroscopic confirmation of a galaxy cluster at z = 2.095 in the COSMOS field. This galaxy cluster was first reported in the ZFOURGE survey as harboring evolved massive galaxies using photometric redshifts derived with deep near-infrared (NIR) medium-band filters. We obtain medium-resolution (R ∼ 3600) NIR spectroscopy with MOSFIRE on the Keck 1 telescope and secure 180 redshifts in a 12′ x 12′ region. We find a prominent spike of 57 galaxies at z = 2.095 corresponding to the galaxy cluster. The cluster velocity dispersion is measured to be σv1D = 552 ± 52 km s-1. This is the first study of a galaxy cluster in this redshift range (z ≳ 2.0) with the combination of spectral resolution (∼26 km s-1) and the number of confirmed members (>50) needed to impose a meaningful constraint on the cluster velocity dispersion and map its members over a large field of view. Our ΛCDM cosmological simulation suggests that this cluster will most likely evolve into a Virgo-like cluster with Mvir = 1014.4±0.3 M (68% confidence) at z ∼ 0. The theoretical probability of finding such a cluster is ∼4%. Our results demonstrate the feasibility of studying galaxy clusters at z > 2 in the same detailed manner using multi-object NIR spectrographs as has been done in the optical in lower-redshift clusters.

    Original languageEnglish
    Article numberL20
    Pages (from-to)1-6
    Number of pages6
    JournalAstrophysical Journal Letters
    Issue number1
    Publication statusPublished - 1 Nov 2014

    Bibliographical note

    Copyright the American Astronomical Society. First published in Astrophysical journal letters, volume 795, issue 1, article L20. The original publication is available at, published by IOP Publishing. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


    • galaxies: clusters: general
    • galaxies: high-redshift
    • large-scale structure of universe


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