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arXiv · 0906.4489

Witnessing the assembly at z=1.6 of a galaxy cluster (GMASS ultradeep spectroscopy of galaxies at z~2 - V)

J. Kurk·A. Cimatti·G. Zamorani·C. Halliday·M. Mignoli·L. Pozzetti·E. Daddi·P. Rosati·M. Dickinson·M. Bolzonella·P. Cassata·A. Renzini·A. Franceschini·G. Rodighiero·S. Berta
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Abstract

We present a study of a galaxy overdensity at z=1.6, Cl 0332-2742, uncovered in the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). We conservatively estimate the overdensity in redshift space for the spike, containing 42 galaxies at z=1.6, to be 8.3+/-1.5 and find a velocity dispersion of 500 km/s. A map of the surface density of galaxies at z=1.6 in the GMASS field shows that its structure is irregular. The differences in the physical properties of Cl 0332-2742 member and field galaxies agree with the latest hierarchical galaxy formation models: for overdensity members, the star formation rate (SFR), and specific SFR, is approximately 50% lower than for the field galaxies; overdensity galaxies are twice the age, on average, of field galaxies; and there is a higher proportion of both massive (M>10^{10.7} M_sol), and early-type galaxies, inside Cl 0332-2742 than in the field. Among the 42 members, 7 have spectra consistent with being passively evolving, massive galaxies. In a z-J colour-magnitude diagram, the photometric data of these early-type galaxies are in close agreement with a theoretical red sequence of a galaxy cluster at redshift z=1.6, which formed most of its stars in a short burst of star formation at z~3. We conclude that the redshift spike at z=1.6 in the GMASS field represents a sheet-like structure in the cosmic web and the area with the highest surface density within this structure, containing already seven passively evolving galaxies, will evolve into a cluster of galaxies at a later time.

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J. Kurk, A. Cimatti, G. Zamorani, C. Halliday, M. Mignoli, L. Pozzetti, E. Daddi, P. Rosati, M. Dickinson, M. Bolzonella, P. Cassata, A. Renzini, A. Franceschini, G. Rodighiero, S. Berta. 2009-06-24. Witnessing the assembly at z=1.6 of a galaxy cluster (GMASS ultradeep spectroscopy of galaxies at z~2 - V). https://doi.org/10.1051/0004-6361%2F200809964

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