Galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z = 1.58^⋆,⋆⋆

Red-sequence formation, massive galaxy assembly, and central star formation activity

¹ INAF – Osservatorio Astronomico di Roma (OAR), via Frascati 33, 00040 Monteporzio Catone, Italy
e-mail: rene.fassbender@oa-roma.inaf.it
² Max-Planck-Institut für extraterrestrische Physik (MPE), Postfach 1312, Giessenbachstr., 85741 Garching, Germany
³ Institut d’Astrophysique Spatiale, Bâtiment 12, Université Paris-Sud, 91405 Orsay, France
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁵ European Space Astronomy Centre (ESAC), 7828691 Villanueva de la Canada, Madrid, Spain
⁶ Australian Astronomical Observatory, PO BOX 915, North Ryde 1670, Australia
⁷ University of Vienna, Department of Astronomy, Türkenschanzstraße 17, 1180 Vienna, Austria
⁸ Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁹ National Astronomical Observatory of Japan, Mitaka, 181-8588 Tokyo, Japan
¹⁰ Università degli Studi di Ferrara, Via Savonarola 9, 44121 Ferrara, Italy
¹¹ European Southern Observatory (ESO), Karl-Scharzschild-Str. 2, 85748 Garching, Germany
¹² Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306 Santiago 22, Chile
¹³ INAF – Osservatorio Astrofisico, via S.Sofia 78, 95123 Catania, Italy
¹⁴ CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
¹⁵ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia
¹⁶ Department of Physics, Ludwig-Maximilians Universität München, Scheinerstr. 1, 81679 Munich, Germany

Received: 3 April 2014
Accepted: 5 June 2014

Abstract

Context. Recent observational progress has enabled the detection of galaxy clusters and groups out to very high redshifts and for the first time allows detailed studies of galaxy population properties in these densest environments in what was formerly known as the “redshift desert” at z> 1.5.

Aims. We aim to investigate various galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z = 1.58, which constitutes the most extreme currently known matter-density peak at this redshift.

Methods. We analyzed deep VLT/HAWK-I near-infrared data with an image quality of 0.5′′ and limiting Vega magnitudes (50% completeness) of 24.2 in J- and 22.8 in the Ks band, complemented by similarly deep Subaru imaging in i and V, Spitzer observations at 4.5 μm, and new spectroscopic observations with VLT/FORS 2.

Results. We detect a cluster-associated excess population of about 90 galaxies, most of them located within the inner 30′′ (250 kpc) of the X-ray centroid, which follows a centrally peaked, compact NFW galaxy surface-density profile with a concentration of c₂₀₀ ≃ 10. Based on the Spitzer 4.5 μm imaging data, we measure a total enclosed stellar mass of M∗₅₀₀ ≃ (6.3 ± 1.6) × 10¹² M_⊙ and a resulting stellar mass fraction of f_∗,500 = M_∗,500/M₅₀₀ = (3.3 ± 1.4)%, consistent with local values. The total J- and Ks-band galaxy luminosity functions of the core region yield characteristic magnitudes J* and Ks* consistent with expectations from simple z_f = 3 burst models. However, a detailed look at the morphologies and color distributions of the spectroscopically confirmed members reveals that the most massive galaxies are undergoing a very active mass-assembly epoch through merging processes. Consequently, the bright end of the cluster red sequence is not in place, while a red-locus population is present at intermediate magnitudes [Ks*, Ks* + 1.6], which is then sharply truncated at magnitudes fainter than Ks* + 1.6. The dominant cluster-core population comprises post-quenched galaxies transitioning toward the red sequence at intermediate magnitudes, while additionally a significant blue-cloud population of faint star-forming galaxies is present even in the densest central regions. Based on a color−color selection performed to separate different cluster galaxy types, we find that the blue star-forming population is concentrated in clumpy structures and dominates in particular at and beyond the R₅₀₀ radius. On the other hand, the fraction of post-starburst galaxies steadily increases toward the center, while the red-locus population and red-sequence transition galaxies seem to reach their peak fractions already at intermediate cluster-centric radii of about r ~ 200 kpc.

Conclusions. Our observations support the scenario in which the dominant effect of the dense z ≃ 1.6 cluster environment is an accelerated mass-assembly timescale (~1 Gyr or shorter) through merging activity that is responsible for driving core galaxies across the mass-quenching threshold of log (M_∗/M_⊙) ≃ 10.4. Beyond this mass limit, star formation is suppressed on timescales of ~1 Gyr, while the direct environmental quenching process seems to be subdominant and is acting on significantly longer timescales (~2−3 Gyr).