KECK/MOSFIRE SPECTROSCOPIC CONFIRMATION OF A VIRGO-LIKE CLUSTER ANCESTOR AT z = 2.095

Abstract

We present the 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 ′ × 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 σ v1D = 552 ± 52 km/s. 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) 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 M vir =10 14.4±0.3 M ⊙ (68% confidence) at z ∼ 0. The theoretical expectation 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.

Passive galaxies as tracers of cluster environments atz~ 2

“…An overdensity at a consistent position and redshift is also visible in Scoville et al (2013) density maps. We also note the proximity (a few to 14 Mpc) of confirmed/candidate structures at similar redshift (Diener et al 2014;Castignani et al 2014;Chiang et al 2014;Yuan et al 2014). …”

A GIANT LYα NEBULA IN THE CORE OF AN X-Ray CLUSTER AT Z = 1.99: IMPLICATIONS FOR EARLY ENERGY INJECTION

“…We note that CL1449+0856 is not anomalous in terms of star formation activity with respect to potentially similar structures at comparable redshift (i.e., Tran et al 2010;Yuan et al 2014;Gobat et al 2015;Santos et al 2015) and it is globally consistent with the tracks reported in Figure 9 based on the model by Béthermin et al (2013). The instantaneous energy input from AGN corresponds only to L 0.05 bol AGN , a factor of three timeslower than typically assumed in simulations (Section 4.3), supporting the estimate of the mass outflow rates reported in Section 4.1, while from star formation it is just L 0.003 bol SFGs .…”

Z-FIRE: ISM PROPERTIES OF THEz= 2.095 COSMOS CLUSTER

“…With this technique, the COSMOS cluster was revealed with photometric redshifts z 2.2 (Spitler et al 2012). Subsequent Keck observations revealed 57 spectroscopically confirmed cluster members within a projected radius of ∼5 Mpc at z = 2.095 (Yuan et al 2014). We compare the ISM properties of the COSMOS cluster with two comparison field samples.…”