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Register a new userThe Galaxy Populations of Double Cluster RX J1053.7+5735 at z=1.13
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We present a study of the galaxy population in the cluster RX J1053.7+5735, one of the most distant X-ray selected clusters of galaxies, which also shows an unusual double-lobed X-ray morphology, indicative of a possible equal-mass cluster merger. Using Keck-DEIMOS spectroscopic observations of galaxies in the 2x1.5 arcmin region surrounding RX J1053.7+5735, we secured redshifts for six galaxies in the range 1.129 < z < 1.139, with a mean redshift <z>=1.134. The mean redshift agrees well with the cluster X-ray redshift previously estimated from the cluster X-ray Fe-K line, confirming the presence of a cluster at z~1.135. Galaxies with concordant redshifts are located in both eastern and western sub-clusters of the double cluster structure, indicating that both sub-clusters are at similar redshifts. This result is also consistent with a previous claim that both eastern and western X-ray lobes have similar X-ray redshifts. Based on their separation of ~ 250 kpc/h, these results support the interpretation that RX J1053.7+5735 is an equal-mass cluster merger taken place at z ~ 1, although further direct evidence for dynamical state of the cluster is needed for a more definitive statement about the cluster merging state. The six galaxies have a line-of-sight velocity dispersion = 650 km/s. All six galaxies show clear absorption features of CaII H & K, and several Balmer lines, typical of early galaxies at the present epoch, in agreement with their I-K colors. A color-magnitude diagram, constructed from deep optical/NIR observations of the RX J1053.7+5735 field, shows a clear red color sequence. There is an indication that the red sequence in RX J1053.7+5735 lies ~ 0.3 to the blue of the Coma line, qualitatively consistent with previous studies investigating other clusters at z ~ 1.
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We present the Fundamental Plane (FP) in the z = 0.28 cluster of galaxies RX J0142.0+2131. There is no evidence for a difference in the slope of the FP when compared with the Coma cluster, although the internal scatter is larger. On average, stellar populations in RX J0142.0+2131 have rest-frame V-band mass-to-light ratios (M/L_V) 0.29+-0.03 dex lower than in Coma. This is significantly lower than expected for a passively-evolving cluster formed at z_f=2. Lenticular galaxies have lower average M/L_V and a distribution of M/L_V with larger scatter than ellipticals. Lower mass-to-light ratios are not due to recent star formation: our previous spectroscopic observations of RX J0142.0+2131 E/S0 galaxies showed no evidence for significant star-formation within the past ~4 Gyr. However, cluster members have enhanced alpha-element abundance ratios, which may act to decrease M/L_V. The increased scatter in the RX J0142.0+2131 FP reflects a large scatter in M/L_V implying that galaxies have undergone bursts of star formation over a range of epochs. The seven easternmost cluster galaxies, including the second brightest member, have M/L_V consistent with passive evolution and z_f = 2. We speculate that RX J0142.0+2131 is a cluster-cluster merger where the galaxies to the east are yet to fall into the main cluster body or have not experienced star formation as a result of the merger.
The thesis work is focused on the analysis of the galaxy clusters ABCG 209, at z~0.2, which is characterized by a strong dynamical evolution. The data sample used is based mainly on new optical data (EMMI-NTT: B, V and R band images and MOS spectra), acquired in October 2001 at the European Southern Observatory in Chile. Archive optical data (CFHR12k: B and R images), and X-ray (Chandra) and radio (VLA) observations are also analysed. The main goal of the present analysis is the investigation of the connection between internal cluster dynamics and star formation history, aimed at understanding the complex mechanisms of cluster formation and evolution. The analysis of the internal dynamics of the cluster and the study of the galaxy luminosity function (LF) suggest an observational scenario in which ABCG 209 is undergoing a strong dynamical evolution with the merging of two or more subclumps along the SE-NW direction in a plane which is not parallel to the plane of sky. The effect of cluster environment on the global properties of the cluster galaxies is examined through the analysis of the LFs, colour-magnitude relations, and average colours.Moreover cluster dynamics and large-scale structure have a strong influence on galaxy evolution, so it is performed a detailed study of spectroscopic properties of 102 luminous member galaxies. All the results support an evolutionary scenario in which ABCG 209 is characterized by a sum of two components: an old galaxy population, formed very earlier (z >~ 3), and a younger population of infalling galaxies. Moreover this cluster may have experimented 1 or 2 Gyrs ago a merging with an infalling galaxy group, as indicated also by the previous dynamical analysis.
We report on a 20 ksec XMM observation of the distant cluster RXJ1120.1+4318, discovered at z=0.6 in the SHARC survey. The cluster has a regular spherical morphology, suggesting it is in a relaxed state. The combined fit of the EPIC/MOS&pn camera gives a cluster mean temperature of kT=5.3pm0.5 keV with an iron abundance of 0.47pm0.19. The temperature profile, measured for the first time at such a redshift, is consistent with an isothermal atmosphere up to half the virial radius. The surface brightness profile, measured nearly up to the virial radius, is well fitted by a beta-model, with beta =0.78[+0.06,-0.04] and a core radius of thetac = 0.44[+0.06,-0.04] arcmin. We compared the properties of RXJ1120.1+4318 with the properties of nearby clusters for two cosmological models: an Einstein - de Sitter Universe and a flat low density Universe with Omega0=0.3. For both models, the scaled emission measure profile beyond the core, the gas mass fraction and luminosity are consistent with the expectations of the self-similar model of cluster formation, although a slightly better agreement is obtained for a low density Universe. There is no evidence of a central cooling flow, in spite of the apparent relaxed state of the cluster. This is consistent with its estimated cooling time, larger than the age of the Universe at the cluster redshift. The entropy profile shows a flat core with a central entropy of ~ 140 keV cm^2, remarkably similar to the entropy floor observed in nearby clusters, and a rising profile beyond typically 0.1 virial radius. Implications of our results, in terms of non-gravitational physics in cluster formation, are discussed.
SPT-CL J2106-5844 is among the most massive galaxy clusters at z>1 yet discovered. While initially used in cosmological tests to assess the compatibility with $Lambda$CDM cosmology of such a massive virialized object at this redshift, more recent studies indicate SPT-CL J2106-5844 is undergoing a major merger, and is not an isolated system with a singular, well-defined halo. We use sensitive, high spatial resolution measurements from ALMA and ACA of the thermal SZ effect to reconstruct the pressure distribution of the intracluster medium in this system. These measurements are coupled with radio observations from the EMU pilot survey, using ASKAP and the ATCA to search for diffuse nonthermal emission. Further, to better constrain the thermodynamic structure of the cluster, we complement our analysis with reprocessed archival $Chandra$ observations. We fit the ALMA+ACA SZ data in $uv$-space using a Bayesian forward modelling technique. The ASKAP and ATCA data are processed and imaged to specifically highlight any potential diffuse radio emission. In the ALMA+ACA SZ data, we reliably identify at high significance two main gas components associated with the mass clumps inferred from weak lensing. Our statistical test excludes at the ~9.9$sigma$ level the possibility of describing the system with a single SZ component. While the components had been more difficult to identify in the X-ray data alone, we find that the bimodal gas distribution is supported by the X-ray hardness distribution. The EMU radio observations reveal a diffuse radio structure ~400 kpc in projected extent along the northwest-southeast direction, indicative of strong activity from the active galactic nucleus within the brightest cluster galaxy. Interestingly, a putative optical star-forming filamentary structure detected in the HST image is in an excellent alignment with the radio structure, albeit on a smaller scale.
We present a study of the stellar populations of galaxies in the cluster RXJ0152.7-1357 at a redshift of 0.83. The study is based on new high S/N spectroscopy of 29 cluster members covering the wavelength range 5000-10000A as well as riz photometry of the cluster. The scaling relations between velocity dispersions, luminosities and Balmer line strengths appear to be in agreement with pure passive evolution of the stellar populations with a formation redshift z=4. However, the strengths of the D4000 indices and the metal indices do not support this interpretation. Compared to z=0, the metal indices (C4668, Fe4383, CN3883, G4300 and CN2) show that at least half of the non-emission line galaxies in RXJ0152.7-1357 have [alpha/Fe] of 0.2 dex higher, and about half of the galaxies have significantly lower metal content. The differences in stellar populations of the galaxies are associated with the location of the galaxies relative to the X-ray emission. The galaxies with weak C4668 and G4300, as well as galaxies with weak [OII] emission, are located in areas of low X-ray luminosity. It is possible that these galaxies are experiencing the effect of the cluster merger taking place in RXJ0152.7-1357 as (short) episodes of star formation, while the galaxies in the cores of the X-ray sub-clumps are unaffected by the merger. The spectroscopy of the RXJ0152.7-1357 galaxies shows for the first time galaxies in a rich cluster at intermediate redshift that cannot evolve passively into the present day galaxy population in rich clusters. Additional physical processes may be at work and we speculate that merging with infalling (disk) galaxies in which stars have formed over an extended period might produce the required reduction in [alpha/Fe]. (abridged)
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