Composite images of MACS galaxy clusters from the University of Hawaii's 2.2-meter telescope

The following false-color composite images of newly discovered MACS clusters were generated from separate images in the V, R, and I bands taken with the University of Hawaii's 2.2m telescope. Galaxies in the cluster appear as fuzzy yellowish blobs in this rendering, while galaxies in the foreground (closer to us) appear bluer and galaxies in the background (farther away from us) appear redder. Non diffuse, bright objects are foreground stars. Each image spans 5 arcminutes or (at this distance) about 6-7 million light years across. North is up and east is to the left. We assume a value of h=0.5 for the normalized Hubble constant when computing linear distances. See captions for more details on the individual clusters.

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Figure 1. An example of a dynamically "relaxed" MACS cluster at a redshift of z=0.390 (6.2 billion light years away). The galaxy distribution is relatively symmetric and dominated by a single central galaxy, which also lies at the center of the X-ray emission. These extremely luminous galaxies are the largest collections of stars in the Universe. Many of the less luminous galaxies in the cluster core have already been swallowed by the central giant, contributing to its growth over the billions of year since the initial formation of this cluster. A few much more nearby galaxies appear as blueish-white blobs, three of them due south of the cluster core. The image spans about 1.9 Mpc (6.2 million light years) on the side at the redshift of the cluster.

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Figure 2. This very galaxy-rich MACS cluster at a redshift of z=0.453 (7 billion light years away) exhibits very strong sub-clustering (note the clumpiness of the galaxy distribution). This system is either still in the process of formation or has recently been disrupted by the infall of a previously separate group or cluster of galaxies. In either case a more homogeneous, "relaxed" cluster similar in appearance to the one shown in Figure 1 is likely to emerge in several billion years. The image spans about 2 Mpc (6.7 million light years) on the side at the redshift of the cluster.

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Figure 3a. One of the most distant MACS clusters discovered so far: z=0.540 (almost 8 billion light years away). Again the galaxy distribution appears very non-homogeneous. A first measurement of the radial velocity dispersion of the cluster galaxies suggests that this system may be one of the most massive clusters known at any redshift. The image spans 2.2 Mpc (6.8 million light years) on the side at the redshift of the cluster.

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Figure 3b. The same MACS cluster as shown in Figure 3a. Overlaid in white are the contours of the X-ray emission as measured in a long, dedicated observation of the cluster with the ROSAT HRI detector. The X-ray emission originates from diffuse hot gas spread throughout the cluster. As is evident from this overlay, the distribution of the gas can be very different from that of the galaxies, particularly in clusters that have yet to reach a state of equilibrium, for instance, after merging with another group or cluster of galaxies which we suspect to be the case for this system.