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Post Info TOPIC: JKCS041
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Title: JKCS041: a Coma cluster progenitor at z=1.803
Author: S. Andreon, A. B. Newman, G. Trinchieri, A. Raichoor, R. S. Ellis, T. Treu

Using deep two-color near-infrared HST imaging and unbiased grism spectroscopy we present a detailed study of the z=1.803 JKCS041 cluster. Uniquely, for a high redshift cluster, we confirm a mass of logM=14.2 in solar units using four different techniques based on the X-ray temperature, the X-ray luminosity and the cluster richness. JKCS041 is thus a progenitor of a local system like the Coma cluster. Our rich dataset and the abundant population of 14 spectroscopically-confirmed red sequence galaxies allows us to explore the past star formation history of this system in unprecedented detail. Remarkably, we find a prominent red sequence down to stellar masses as low as logM=9.8, corresponding to a mass range of 2 dex. These quiescent galaxies are concentrated around the cluster center with a core radius of 330 kpc. Blue members are few and avoid the cluster center. In JKCS041 quenching was therefore largely completed by a look-back time of 10 Gyr and we can constrain the epoch at which this occurred via spectroscopic age-dating of the individual galaxies. Most galaxies were quenched about 1.1 Gyr prior to the epoch of observation. The less massive quiescent galaxies are somewhat younger, corresponding to a decrease in age of 650 Myr per mass dex, but the scatter in age at fixed mass is only 380 Myr (at logM=11). The size-mass relation of quiescent galaxies in JKCS041 is consistent with that observed for local clusters within our uncertainties. Comparing our data on JKCS041 with 41 clusters at lower redshift, we find that the form of the mass function of red sequence galaxies has hardly evolved in the past 10 Gyr, both in terms of its faint end slope and characteristic mass. Despite observing JKCS041 soon after its quenching and the three fold expected increase in mass in the next 10 Gyr, it is already remarkably similar to present-day clusters.

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A group of galaxies has been seen at a record distance from Earth thanks to the assistance of Bristol scientists.
The cluster, named JKCS041, is 10.2 billion light-years away - a billion light-years further away than the current record holder.
Nasa's Chandra X-Ray Observatory made the discovery with other telescopes.

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JKCS041: Galaxy Cluster Smashes Distance Record

* The most distant galaxy cluster yet has been discovered using Chandra and optical and infrared telescopes.
* At some 10.2 billion light years away, the galaxy cluster is seen when the Universe was only one quarter of its current age.
* This object, known as JKCS041, may help scientists better understand how the Universe developed at this crucial stage.

JKCS041 was originally detected in 2006 with infrared observations from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii telescope in Hawaii and NASA's Spitzer Space Telescope. However, scientists were not sure if it was a true galaxy cluster, rather than one that has been caught in the act of forming. The shape and extent of the X-ray emission in the Chandra data, however, provided the definitive evidence that showed that JKCS041 was, indeed, a galaxy cluster. The Chandra data also allowed scientists to rule out other possible explanations for the data, including a group of galaxies, or a filament of galaxies seen along the line of sight.

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Blobrana


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Scientists discover cluster 10.2bn light years from Earth
A galaxy cluster some 10.2 billion light years away has been named as the furthest from Earth ever found.
The group of galaxies, known as JKCS041, beats the previous record holder by around a billion light years. It appears as it was when Earth was only a quarter of its present age.
The bunch, containing hundreds of galaxies, was analysed by combining data from Nasa's Chandra X-Ray Observatory with data from optical and infrared telescopes.

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JKCS041: a colour-detected galaxy cluster at z=1.9 with deep potential well as confirmed by X-ray data.

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Title: JKCS041: a colour-detected galaxy cluster at z=1.9 with deep potential well as confirmed by X-ray data
Authors: S. Andreon, B. Maughan, G. Trinchieri, J. Kurk

We report the discovery of JKCS041, a massive near-infrared selected cluster of galaxies z=1.9. The cluster was originally discovered using a modified red-sequence method and was also detected in follow-up Chandra data as extended X-ray source. Optical and near-infrared imaging data alone allow us to show that the detection of JKCS041 is as secure as the detections of clusters in the REFLEX survey. JKCS041 is also detected using an SED fitting technique, based on photometry in eleven bands. We investigate the possibility that JKCS041 is not a discrete galaxy cluster at z=1.9, and find other explanations to be unlikely. The X-ray detection and statistical arguments rule out the hypothesis that JKCS041 is actually a blend of groups along the line of sight, and we find that the X-ray emitting gas is too hot and dense to be a filament projected along the line of sight. The absence of a central radio source and the extent and morphology of the X-ray emission argue against the possibility that the X-ray emission is due to inverse Compton scattering of CMB photons by a radio plasma. The cluster has an X-ray core radius of 36.6 arcsec (about 300 kpc), an X-ray temperature of 7.6 keV, a bolometric X-ray luminosity within R500 of 7.6 10^44 erg/s, an estimated mass of M500=2.9 10^14 Msol, the latter derived under the usual (and strong) assumptions. The cluster is composed of 16.4 galaxies within 1.5 arcmin (750 kpc) brighter than K~20.7 mag. The high redshift of JKCS041 is determined from the colour of the red sequence, from the detection of the cluster in a galaxy sample formed by zphot>1.6 galaxies, and from SED fitting with z=1.9 red galaxies. Therefore, JKCS041 is a cluster of galaxies at z=1.9 with deep potential well, making it the most distant cluster with extended X-ray emission known.

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