C. -J. Ma

Publications (9)9.8 Total impact

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  Available from: Johan Richard

  Article: Strong Lensing by a Node of the Cosmic Web. The Core of MACS J0717.5+3745 at z=0.55

  M. Limousin, H. Ebeling, J. Richard, A. M. Swinbank, G. P. Smith, M. Jauzac, S. Rodionov, C. -J. Ma, I. Smail, A. C. Edge, E. Jullo, J. P. Kneib
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  ABSTRACT: We present results of a strong-lensing analysis of MACS J0717.5+3745 (hereafter MACS J0717), an extremely X-ray luminous galaxy cluster at z=0.55. Observations at different wavelengths reveal a complex and dynamically very active cluster, whose core is connected to a large scale filament extended over several Mpc. Using multi-passband imaging data obtained with the Hubble Space Telescope Advanced Camera for Surveys (ACS), we identify 15 multiply imaged systems across the full field of view of ACS, five of which we confirmed spectroscopically in groundbased follow-up observations with the Keck telescope. We use these multiply imaged systems to constrain a parametric model of the mass distribution in the cluster core, employing a new parallelized version of the Lenstool software. The main result is that the most probable description of the mass distribution comprises four cluster-scale dark matter haloes. The total mass distribution follows the light distribution but strongly deviates from the distribution of the intra-cluster gas as traced by the X-ray surface brightness. This confirms the complex morphology proposed by previous studies. We interpret this segregation of collisional and collisionless matter as strong evidence of multiple mergers and ongoing dynamical activity. MACS J0717 thus constitutes one of the most disturbed clusters presently known and, featuring a projected mass within the ACS field of view (R=150"=960 kpc) of 2.11 +- 0.23 x 10^{15} M_{sun}, the system is also one of the most massive known.
  09/2011;
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  Available from: Harald Ebeling

  Article: The morphology–density relation of galaxies around MACS J0717.5+3745★

  C.-J. Ma, H. Ebeling
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  ABSTRACT: We use an 18 × 9 arcmin2 mosaic of HST/ACS images covering the entire large-scale structure around the X-ray luminous cluster MACSJ0717.5+3745 (z= 0.545) to study the morphology of galaxies at the cluster redshift. We find the global fraction of morphological types of galaxies to be consistent with results in the literature. In addition, we confirm the morphology–density relation of both early-type and late-type galaxies. Interestingly, we find that the fraction of lenticular galaxies (S0) also correlates with local galaxy density, in contrast to the findings of a study of the cores of 10 clusters at similar redshift by Dressler et al. We suggest that this apparent inconsistency is due to differences in the spatial coverage around clusters, which is supported by the fact that the correlation disappears for S0s within a radius of 0.6R200 of MACSJ0717.5+3745. We interpret this result as evidence of the morphology–density relation being caused by a combination of morphological transformation triggered by galaxy–galaxy interactions, and effects related to the formation and evolution of large-scale structure. In environments of low to intermediate density, where galaxy–galaxy interactions are frequent and efficient, the observed pronounced morphology–density relation for S0s reflects the density dependence of the interaction cross-section. In clusters, however, the correlation disappears for S0s, as the much higher galaxy velocities in clusters not only lower the interaction cross-section, but also cause a spatial redistribution of galaxies that all but destroys such a correlation. This argument does not hold for elliptical galaxies in clusters which, having formed much earlier, have settled into the large-scale cluster potential; hence the morphology–density relation for cluster ellipticals may reflect primarily the state of advanced dynamical relaxation of this population within the cluster rather than a causal link to the environment responsible for the morphological transformation of galaxies.
  Monthly Notices of the Royal Astronomical Society 01/2011; 410(4):2593 - 2601. · 4.90 Impact Factor
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  Available from: ArXiv

  Article: The morphology-density relation of galaxies around MACSJ0717.5+3745

  C. -J. Ma, H. Ebeling
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  ABSTRACT: We use an 18' x 9' mosaic of ACS images covering the entire large-scale structure around the X-ray luminous cluster MACSJ0717.5 (z=0.545) to study the morphology of galaxies at the cluster redshift. We find the global fraction of morphological types of galaxies to be consistent with results in the literature. Interestingly, we find that the fraction of S0s also correlates with local galaxy density, in contrast to the findings of a study of the cores of 10 clusters at similar redshift by Dressler et al. We suggest that this apparent inconsistency is due to differences in the spatial coverage around clusters, which is supported by the fact that the correlation disappears for S0s within a radius of 0.6R_200 of MACSJ0717. We interpret this result as evidence of the morphology-density relation being caused by a combination of morphological transformation triggered by galaxy-galaxy interactions, and effects related to the formation and evolution of large-scale structure. In environments of low to intermediate density, where galaxy-galaxy interactions are frequent and efficient, the observed pronounced morphology-density relation for S0s reflects the density dependence of the interaction cross section. In clusters, however, the correlation disappears for S0s, as the much higher galaxy velocities in clusters not only lower the interaction cross section, but also cause a spatial redistribution of galaxies that all but destroys such a correlation. This argument does not hold for elliptical galaxies in clusters which, having formed much earlier, have settled into the large-scale cluster potential; hence the morphology-density relation for cluster ellipticals may reflect primarily the state of advanced dynamical relaxation of this population within the cluster rather than a causal link to the environment responsible for the morphological transformation of galaxies. Comment: accepted by MNRAS; Full resolution version of fig 1 and fig 2 will be published in the journal
  09/2010;
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  Available from: Arlan W Mantz

  Article: The X-ray brightest clusters of galaxies from the Massive Cluster Survey

  H. Ebeling, A. C. Edge, A. Mantz, E. Barrett, J. P. Henry, C. -J. Ma, L. van Speybroeck
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  ABSTRACT: We present a statistically complete sample of very X-ray luminous galaxy clusters detected in the MAssive Cluster Survey (MACS). This second MACS release comprises all 34 MACS clusters with nominal X-ray fluxes in excess of 2x10^(-12) erg/s/cm^2 (0.1-2.4 keV) in the ROSAT Bright Source Catalogue; two thirds of them are new discoveries. Extending over the redshift range from 0.3 to 0.5, this subset complements the complete sample of the 12 most distant MACS clusters (z>0.5) published in 2007 and further exemplifies the efficacy of X-ray selection for the compilation of samples of intrinsically massive galaxy clusters. Extensive follow-up observations with Chandra/ACIS led to three additional MACS cluster candidates being eliminated as (predominantly) X-ray point sources. For another four clusters --- which, however, remain in our sample of 34 --- the point-source contamination was found to be about 50%. The median X-ray luminosity of 1.3x10^45 erg/s (0.1-2.4 keV, Chandra, within r_500) of the clusters in this subsample demonstrates the power of the MACS survey strategy to find the most extreme and rarest clusters out to significant redshift. A comparison of the optical and X-ray data for all clusters in this release finds a wide range of morphologies with no obvious bias in favour of either relaxed or merging systems. Comment: 10 pages, 6 figures, 2 tables; accepted for publication in MNRAS
  04/2010;
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  Available from: Phil Marshall

  Article: The impact of a major cluster merger on galaxy evolution in MACS\,J0025.4-1225

  C. -J. Ma, H. Ebeling, P. Marshall, T. Schrabback
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  ABSTRACT: We present results of an extensive morphological, spectroscopic, and photometric study of the galaxy population of MACS J0025.4$-$1225 (z=0.586), a major cluster merger with clear segregation of dark and luminous matter, to examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra obtained with Keck DEIMOS, we identified 212 cluster members within 4 Mpc of the cluster centre, and classified them using three spectroscopic types; we find 111 absorption-line, 90 emission-line (including 23 e(a) and 11 e(b)), and 6 E+A galaxies. The fraction of absorption(emission)-line galaxies is a monotonically increasing(decreasing) function of both projected galaxy density and radial distance to the cluster center. More importantly, the 6 observed E+A cluster members are all located between the dark-matter peaks of the cluster and within ~0.3Mpc radius of the X-ray flux peak, unlike the E+A galaxies in other intermediate-redshift clusters which are usually found to avoid the core region. In addition, we use Hubble Space Telescope imaging to classify cluster members according to morphological type. We find the global fraction of spiral and lenticular galaxies in MACS J0025 to be among the highest observed to date in clusters at z>0.5. The observed E+A galaxies are found to be of lenticular type with Sersic indices of ~2, boosting the local fraction of S0 to 70 per cent between the dark-matter peaks. Combing the results of our analysis of the spatial distribution, morphology, and spectroscopic features of the galaxy population, we propose that the starburst phase of these E+A galaxies was both initiated and terminated during the first core-passage about 0.5--1Gyr ago, and that their morphology has already been transformed into S0 due to ram pressure and/or tidal forces near the cluster core. By contrast, ongoing starbursts are observed predominantly in infalling galaxies, and thus appears to be unrelated to the cluster merger. Comment: 18 pages, 17 figures, accepted by MNRAS
  03/2010;
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  Available from: Johan Richard

  Article: MACSJ1423.8+2404: Gravitational Lensing by a Massive, Relaxed Cluster of Galaxies at z=0.54

  M. Limousin, H. Ebeling, C. -J. Ma, A. M. Swinbank, G P Smith, J. Richard, A. C. Edge, M. Jauzac, J. -P. Kneib, P. Marshall, T. Schrabback
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  ABSTRACT: We present results of a gravitational-lensing and optical study of MACS ,J1423.8+2404 (z=0.545, MACS, J1423). Our analysis uses high-resolution images taken with the Hubble Space Telescope in the F555W and F814W passbands, ground based imaging in eight optical and near-infrared filters obtained with Subaru and CFHT, as well as extensive spectroscopic data gathered with the Keck telescopes. At optical wavelengths the cluster exhibits no sign of substructure and is dominated by a cD galaxy that is 2.1 magnitudes (K-band) brighter than the second brightest cluster member, suggesting that MACS, J1423 is close to be fully virialized. Analysis of the redshift distribution of 140 cluster members reveals a Gaussian distribution, mildly disturbed by the presence of a loose galaxy group that may be falling into the cluster along the line of sight. Combining strong-lensing constraints from two spectroscopically confirmed multiple-image systems near the cluster core with a weak-lensing measurement of the gravitational shear on larger scales, we derive a parametric mass model for the mass distribution. All constraints can be satisfied by a uni-modal mass distribution centred on the cD galaxy and exhibiting very little substructure. The derived projected mass of M(<65\arcsec [415 kpc])=(4.3\pm0.6)\times 10^{14} M_sun is about 30% higher than the one derived from X-ray analyses assuming spherical symmetry, suggesting a slightly prolate mass distribution consistent with the optical indication of residual line-of-sight structure. The similarity in shape and excellent alignment of the centroids of the total mass, K-band light, and intra-cluster gas distributions add to the picture of a highly evolved system [ABRIDGED] Comment: Resubmitted to MNRAS. High resolution available at http://www.dark-cosmology.dk/~marceau/1423mnras.pdf
  11/2009;
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  Available from: Harald Ebeling

  Article: A spectacular giant arc in the massive cluster lens MACS J1206.2−0847★

  H. Ebeling, C. J. Ma, J.-P. Kneib, E. Jullo, N. J. D. Courtney, E. Barrett, A. C. Edge, J.-F. Le Borgne
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  ABSTRACT: We discuss the X-ray and optical properties of the massive galaxy cluster MACS J1206.2−0847 (z= 0.4385), discovered in the Massive Cluster Survey (MACS). Our Chandra observation of the system yields a total X-ray luminosity of 2.4 × 1045 erg s−1 (0.1–2.4 keV) and a global gas temperature of 11.6 ± 0.7 keV, very high values typical of MACS clusters. In both optical and X-ray images, MACS J1206.2−0847 appears close to relaxed in projection, with a pronounced X-ray peak at the location of the brightest cluster galaxy (BCG); we interpret this feature as the remnant of a cold core. A spectacular giant gravitational arc, 15 arcsec in length, bright (V∼ 21) and unusually red (R−K= 4.3), is seen 20 arcsec west of the BCG; we measure a redshift of z= 1.036 for the lensed galaxy. From our Hubble Space Telescope image of the cluster, we identify the giant arc and its counter image as a sevenfold imaged system. An excess of X-ray emission in the direction of the arc coincides with a mild galaxy overdensity and could be the remnant of a minor merger with a group of galaxies. We derive estimates of the total cluster mass as well as of the mass of the cluster core using X-ray, dynamical and gravitational-lensing techniques. For the mass enclosed by the giant arc (r < 119 kpc), our strong-lensing analysis based on Hubble Space Telescope imaging yields a very high value of 1.1 × 1014 M⊙, inconsistent with the much lower X-ray estimate of 0.5 × 1014 M⊙. Similarly, the virial estimate of 4 × 1015 M⊙ for the total cluster mass, derived from multi-object spectroscopy with Canada–France–Hawaii Telescope (CFHT) and the VLT of 38 cluster members, is significantly higher than the corresponding X-ray estimate of 1.7 × 1015 M⊙. We take the discrepancy between X-ray and other mass estimates to be indicative of pronounced substructure along the line of sight during an ongoing merger event, an interpretation that is supported by the system's very high velocity dispersion of 1580 km s−1.
  Monthly Notices of the Royal Astronomical Society 05/2009; 395(3):1213 - 1224. · 4.90 Impact Factor
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  Available from: arxiv.org

  Article: A complete sample of twelve very X-ray luminous galaxy clusters at z>0.5

  H. Ebeling, E. Barrett, D. Donovan, C. -J. Ma, A. C. Edge, L. van Speybroeck
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  ABSTRACT: We present the statistically complete and cosmologically most relevant subset of the twelve most distant galaxy clusters detected at z>0.5 by the MAssive Cluster Survey (MACS). Ten of these systems are new discoveries; only two (MACSJ0018.5+1626 aka CL0016+1609, and MACSJ0454.1-0300 aka MS0451.6-0305) were previously known. We provide fundamental cluster properties derived from our optical and X-ray follow-up observations as well as the selection function in tabulated form to facilitate cosmological studies using this sample. Comment: Four pages, 1 figure, submitted to ApJ
  03/2007;
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  Available from: Marceau Limousin

  Article: MACS J1423.8+2404: gravitational lensing by a massive, relaxed cluster of galaxies at z = 0.54

  M. Limousin, H. Ebeling, C. -J. Ma, A. M. Swinbank, G P Smith, J. Richard, A. C. Edge, M. Jauzac, J. -P. Kneib, P. Marshall, T. Schrabback
  [show abstract] [hide abstract]
  ABSTRACT: We present results of a gravitational lensing and optical study of MACS J1423.8+2404 (z=0.545, MACS J1423), the most relaxed cluster in the high-redshift subsample of clusters discovered in the MAssive Cluster Survey (MACS). Our analysis uses high-resolution images taken with the Hubble Space Telescope in the F555W and F814W passbands, ground-based imaging in eight optical and near-infrared filters obtained with Subaru and Canada–France–Hawaii Telescope, as well as extensive spectroscopic data gathered with the Keck telescopes. At optical wavelengths, the cluster exhibits no sign of substructure and is dominated by a cD galaxy that is 2.1 mag (K band) brighter than the second brightest cluster member, suggesting that MACS J1423 is close to be fully virialized. Analysis of the redshift distribution of 140 cluster members reveals a Gaussian distribution, mildly disturbed by the presence of a loose galaxy group that may be falling into the cluster along the line of sight. Combining stronglensing constraints from two spectroscopically confirmed multiple-image systems near the cluster core with a weak-lensing measurement of the gravitational shear on larger scales, we derive a parametric mass model for the mass distribution. All constraints can be satisfied by a unimodal mass distribution centred on the cD galaxy and exhibiting very little substructure. The derived projected mass of M[<65 arcsec (415 kpc)] = (4.3 ± 0.6) × 10^(14) M_☉ is about 30 per cent higher than the one derived from X-ray analyses assuming spherical symmetry, suggesting a slightly prolate mass distribution consistent with the optical indication of residual line-of-sight structure. The similarity in shape and excellent alignment of the centroids of the total mass, K-band light and intracluster gas distributions add to the picture of a highly evolved system. The existence of a massive cluster like MACS J1423, nearly fully virialized only ~7 Gyr after the big bang, may have important implications for models of structure formation and evolution on cosmological time scales.