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Register a new userPressure distribution of the high-redshift cluster of galaxies CL J1226.9+3332 with NIKA
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The thermal Sunyaev-Zeldovich (tSZ) effect is expected to provide a low scatter mass proxy for galaxy clusters since it is directly proportional to the cluster thermal energy. The tSZ observations have proven to be a powerful tool for detecting and studying them, but high angular resolution observations are now needed to push their investigation to a higher redshift. In this paper, we report high angular (< 20 arcsec) resolution tSZ observations of the high-redshift cluster CL J1226.9+3332 (z=0.89). It was imaged at 150 and 260 GHz using the NIKA camera at the IRAM 30-meter telescope. The 150 GHz map shows that CL J1226.9+3332 is morphologically relaxed on large scales with evidence of a disturbed core, while the 260 GHz channel is used mostly to identify point source contamination. NIKA data are combined with those of Planck and X-ray from Chandra to infer the clusters radial pressure, density, temperature, and entropy distributions. The total mass profile of the cluster is derived, and we find $M_{500} = 5.96^{+1.02}_{-0.79} $ x $10^{14} M_{odot}$ within the radius $R_{500} = 930^{+50}_{-43}$ kpc, at a 68% confidence level. ($R_{500}$ is the radius within which the average density is 500 times the critical density at the clusters redshift.) NIKA is the prototype camera of NIKA2, a KIDs (kinetic inductance detectors) based instrument to be installed at the end of 2015. This work is, therefore, part of a pilot study aiming at optimizing tSZ NIKA2 large programs.
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The determination of the thermodynamic properties of clusters of galaxies at intermediate and high redshift can bring new insights into the formation of large-scale structures. It is essential for a robust calibration of the mass-observable scaling relations and their scatter, which are key ingredients for precise cosmology using cluster statistics. Here we illustrate an application of high resolution $(< 20$ arcsec) thermal Sunyaev-Zeldovich (tSZ) observations by probing the intracluster medium (ICM) of the planck-discovered galaxy cluster psz at redshift $z = 0.61$, using tSZ data obtained with the NIKA camera, which is a dual-band (150 and 260~GHz) instrument operated at the IRAM 30-meter telescope. We deproject jointly NIKA and planck data to extract the electronic pressure distribution from the cluster core ($R sim 0.02, R_{500}$) to its outskirts ($R sim 3, R_{500}$) non-parametrically for the first time at intermediate redshift. The constraints on the resulting pressure profile allow us to reduce the relative uncertainty on the integrated Compton parameter by a factor of two compared to the planck value. Combining the tSZ data and the deprojected electronic density profile from xmm allows us to undertake a hydrostatic mass analysis, for which we study the impact of a spherical model assumption on the total mass estimate. We also investigate the radial temperature and entropy distributions. These data indicate that psz is a massive ($M_{500} sim 5.5 times 10^{14}$ M$_{odot}$) cool-core cluster. This work is part of a pilot study aiming at optimizing the treatment of the NIKA2 tSZ large program dedicated to the follow-up of SZ-discovered clusters at intermediate and high redshifts. (abridged)
We present a weak-lensing analysis of the galaxy cluster CL J1226+3332 at z=0.89 using Hubble Space Telescope Advanced Camera for Surveys images. The cluster is the hottest (>10 keV), most X-ray luminous system at z>0.6 known to date. The relaxed X-ray morphology, as well as its high temperature, is unusual at such a high redshift. Our mass reconstruction shows that on a large scale the dark matter distribution is consistent with a relaxed system with no significant substructures. However, on a small scale the cluster core is resolved into two mass clumps highly correlated with the cluster galaxy distribution. The dominant mass clump lies close to the brightest cluster galaxy whereas the other less massive clump is located ~40 (~310 kpc) to the southwest. Although this secondary mass clump does not show an excess in the X-ray surface brightness, the gas temperature of the region is much higher (12~18 keV) than those of the rest. We propose a scenario in which the less massive system has already passed through the main cluster and the X-ray gas has been stripped during this passage. The elongation of the X-ray peak toward the southwestern mass clump is also supportive of this possibility. We measure significant tangential shears out to the field boundary (~1.5 Mpc), which are well described by an Navarro-Frenk-White profile with a concentration parameter of c200=2.7+-0.3 and a scale length of rs=78+-19 (~600 kpc) with chi^2/d.o.f=1.11. Within the spherical volume r200=1.6 Mpc, the total mass of the cluster becomes M(r<r200)=(1.4+-0.2) x 10^15 solar mass. Our weak-lensing analysis confirms that CL1226+3332 is indeed the most massive cluster known to date at z>0.6.
The thermal Sunyaev-Zeldovich effect (tSZ) is a powerful probe to study clusters of galaxies and is complementary with respect to X-ray, lensing or optical observations. Previous arcmin resolution tSZ observations ({it e.g.} SPT, ACT and Planck) only enabled detailed studies of the intra-cluster medium morphology for low redshift clusters ($z < 0.2$). Thus, the development of precision cosmology with clusters requires high angular resolution observations to extend the understanding of galaxy cluster towards high redshift. NIKA2 is a wide-field (6.5 arcmin field of view) dual-band camera, operated at $100 {rm mK}$ and containing $sim 3300$ KID (Kinetic Inductance Detectors), designed to observe the millimeter sky at 150 and 260 GHz, with an angular resolution of 18 and 12 arcsec respectively. The NIKA2 camera has been installed on the IRAM 30-m telescope (Pico Veleta, Spain) in September 2015. The NIKA2 tSZ observation program will allow us to observe a large sample of clusters (50) at redshift ranging between 0.5 and 1. As a pathfinder for NIKA2, several clusters of galaxies have been observed at the IRAM 30-m telescope with the NIKA prototype to cover the various configurations and observation conditions expected for NIKA2.
We present the results of a study investigating the rest-frame ultra-violet (UV) spectral slopes of redshift z~5 Lyman-break galaxies (LBGs). By combining deep Hubble Space Telescope imaging of the CANDELS and HUDF fields with ground-based imaging from the UKIDSS Ultra Deep Survey (UDS), we have produced a large sample of z~5 LBGs spanning an unprecedented factor of >100 in UV luminosity. Based on this sample we find a clear colour-magnitude relation (CMR) at z~5, such that the rest-frame UV slopes (beta) of brighter galaxies are notably redder than their fainter counterparts. We determine that the z~5 CMR is well described by a linear relationship of the form: d beta = (-0.12 +/- 0.02) d Muv, with no clear evidence for a change in CMR slope at faint magnitudes (i.e. Muv > -18.9). Using the results of detailed simulations we are able, for the first time, to infer the intrinsic (i.e. free from noise) variation of galaxy colours around the CMR at z~5. We find significant (12 sigma) evidence for intrinsic colour variation in the sample as a whole. Our results also demonstrate that the width of the intrinsic UV slope distribution of z~5 galaxies increases from Delta(beta)=0.1 at Muv=-18 to Delta(beta)=0.4 at Muv=-21. We suggest that the increasing width of the intrinsic galaxy colour distribution and the CMR itself are both plausibly explained by a luminosity independent lower limit of beta=-2.1, combined with an increase in the fraction of red galaxies in brighter UV-luminosity bins.
We examine the massive colliding cluster El Gordo, one of the most massive clusters at high redshift. We use a free-form lensing reconstruction method that avoids making assumptions about the mass distribution. We use data from the RELICS program and identify new multiply lensed system candidates. The new set of constraints and free-form method provides a new independent mass estimate of this intriguing colliding cluster. Our results are found to be consistent with earlier parametric models, indirectly confirming the assumptions made in earlier work. By fitting a double gNFW profile to the lens model, and extrapolating to the virial radius, we infer a total mass for the cluster of $M_{200c}=(1.08^{+0.65}_{-0.12})times10^{15}$M$_{odot}$. We estimate the uncertainty in the mass due to errors in the photometric redshifts, and discuss the uncertainty in the inferred virial mass due to the extrapolation from the lens model. We also find in our lens map a mass overdensity corresponding to the large cometary tail of hot gas, reinforcing its interpretation as a large tidal feature predicted by hydrodynamical simulations that mimic El Gordo. Finally, we discuss the observed relation between the plasma and the mass map, finding that the peak in the projected mass map may be associated with a large concentration of colder gas, exhibiting possible star formation. El Gordo is one of the first clusters that will be observed with JWST, which is expected to unveil new high redshift lensed galaxies around this interesting cluster, and provide a more accurate estimation of its mass.
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