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Register a new userDiffuse light in the young cluster of galaxies CL J1449+0856 at z=2.07
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Cluster properties do not seem to be changing significantly during their mature evolution phase, for example they do not seem to show strong dynamical evolution at least up to z~0.5, their galaxy red sequence is already in place at least up to z$sim$1.2, and their diffuse light content remains stable up to z~0.8. The question is now to know if cluster properties can evolve more significantly at redshifts notably higher than 1. We propose here to see how the properties of the intracluster light (ICL) evolve with redshift by detecting and analysing the ICL in the X-ray cluster CL J1449+0856 at z=2.07 (discovered by Gobat et al. 2011), based on deep HST NICMOS H band exposures.We used the same wavelet-based method as that applied to 10 clusters between z=0.4 and 0.8 by Guennou et al. (2012). We detect three diffuse light sources with respective total magnitudes of H=24.8, 25.5, and 25.9, plus a more compact object with a magnitude H=25.3. We discuss the significance of our detections and show that they are robust. The three sources of diffuse light indicate an elongation along a north-east south-west axis, similar to that of the distribution of the central galaxies and to the X-ray elongation. This strongly suggests a history of merging events along this direction. While Guennou et al. (2012) found a roughly constant amount of diffuse light for clusters between z~0 and 0.8, we put in evidence at least a 1.5 magnitude increase between z~0.8 and 2. If we assume that the amount of diffuse light is directly linked to the infall activity on the cluster, this implies that CL J1449+0856 is still undergoing strong merging events.
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We present Atacama Large Millimetre Array and Atacama Compact Array observations of the Sunyaev-Zeldovich effect in the z = 2 galaxy cluster Cl J1449+0856, an X-ray-detected progenitor of typical massive clusters in the present day Universe. While in a cleaned but otherwise untouched 92 GHz map of this cluster, little to no negative signal is visible, careful subtraction of known sub-millimetre emitters in the uv plane reveals a decrement at 5$sigma$ significance. The total signal is -190$pm$36 $mu$Jy, with a peak offset by 5-9 ($sim$50 kpc) from both the X-ray centroid and the still-forming brightest cluster galaxy. A comparison of the recovered uv-amplitude profile of the decrement with different pressure models allows us to derive total mass constraints consistent with the $sim$6$times$10$^{13}$ M$_{odot}$ estimated from X-ray data. Moreover, we find no strong evidence for a deviation of the pressure profile with respect to local galaxy clusters, although a slight tension at small-to-intermediate spatial scales suggests a flattened central profile, opposite to what seen in a cool core and possibly an AGN-related effect. This analysis of the lowest mass single SZ detection so far illustrates the importance of interferometers when observing the SZ effect in high-redshift clusters, the cores of which cannot be considered quiescent, such that careful subtraction of galaxy emission is necessary.
We use HST/WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z=2, one of the few bona-fide established clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest that the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterising the inner cluster core with respect to lower density environments. On the other hand, the color-magnitude diagram of this cluster is definitely different from that of lower-redshift (z<1) clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the proto-cluster and established lower-redshift cluster regimes.
We perform a morphological study of 124 spectroscopically confirmed cluster galaxies in the z=0.84 galaxy cluster RX J0152.7-1357. Our classification scheme includes color information, visual morphology, and 1-component and 2-component light profile fitting derived from Hubble Space Telescope riz imaging. We adopt a modified version of a detailed classification scheme previously used in studies of field galaxies and found to be correlated with kinematic features of those galaxies. We compare our cluster galaxy morphologies to those of field galaxies at similar redshift. We also compare galaxy morphologies in regions of the cluster with different dark-matter density as determined by weak-lensing maps. We find an early-type fraction for the cluster population as a whole of 47%, about 2.8 times higher than the field, and similar to the dynamically young cluster MS 1054 at similar redshift. We find the most drastic change in morphology distribution between the low and intermediate dark matter density regions within the cluster, with the early type fraction doubling and the peculiar fraction dropping by nearly half. The peculiar fraction drops more drastically than the spiral fraction going from the outskirts to the intermediate-density regions. This suggests that many galaxies falling into clusters at z~0.8 may evolve directly from peculiar, merging, and compact systems into early-type galaxies, without having the chance to first evolve into a regular spiral galaxy.
We present SCUBA-2 450$mu$m and 850$mu$m data of the mature redshift 2 cluster CLJ1449. We combine this with archival Herschel data to explore the star forming properties of CLJ1449. Using high resolution ALMA and JVLA data we identify potentially confused galaxies, and use the Bayesian inference tool XID+ to estimate fluxes for them. Using archival optical and near infrared data with the energy-balance code CIGALE we calculate star formation rates, and stellar masses for all our cluster members, and find the star formation rate varies between 20-1600M$_{odot}$yr$^{-1}$ over the entire 3Mpc radial range. The central 0.5Mpc region itself has a total star formation rate of 800$pm$200M$_{odot}$yr$^{-1}$, which corresponds to a star formation rate density of (1.2$pm$0.3)$times$10$^{4}$M$_{odot}$yr$^{-1}$Mpc$^{-3}$, which is approximately five orders of magnitude greater than expected field values. When comparing this cluster to those at lower redshifts we find that there is an increase in star formation rate per unit volume towards the centre of the cluster. This indicates that there is indeed a reversal in the star formation/density relation in CLJ1449. Based on the radial star-formation rate density profile, we see evidence for an elevation in the star formation rate density, even out to radii of 3Mpc. At these radii the elevation could be an order of magnitude greater than field values, but the exact number cannot be determined due to ambiguity in the redshift associations. If this is the case it would imply that this cluster is still accreting material which is possibly interacting and undergoing vigorous star-formation.
We present a detailed high-resolution weak-lensing (WL) study of SPT-CL J2106-5844 at z=1.132, claimed to be the most massive system discovered at z > 1 in the South Pole Telescope Sunyaev-Zeldovich (SPT-SZ) survey. Based on the deep imaging data from the Advanced Camera for Surveys and Wide Field Camera 3 on-board the Hubble Space Telescope, we find that the cluster mass distribution is asymmetric, composed of a main clump and a subclump ~640 kpc west thereof. The central clump is further resolved into two smaller northwestern and southeastern substructures separated by ~150 kpc. We show that this rather complex mass distribution is more consistent with the cluster galaxy distribution than a unimodal distribution as previously presented. The northwestern substructure coincides with the BCG and X-ray peak while the southeastern one agrees with the location of the number density peak. These morphological features and the comparison with the X-ray emission suggest that the cluster might be a merging system. We estimate the virial mass of the cluster to be $M_{200c} = (10.4^{+3.3}_{-3.0}pm1.0)~times~10^{14}~M_{odot}$, where the second error bar is the systematic uncertainty. Our result confirms that the cluster SPT-CL J2106-5844 is indeed the most massive cluster at z>1 known to date. We demonstrate the robustness of this mass estimate by performing a number of tests with different assumptions on the centroids, mass-concentration relations, and sample variance.
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