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Post Info TOPIC: ACT-CL J0102-4915
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NASA Hubble Team Finds Monster "El Gordo" Galaxy Cluster Bigger Than Thought

NASA's Hubble Space Telescope has weighed the largest known galaxy cluster in the distant universe, catalogued as ACT-CL J0102-4915, and found it definitely lives up to its nickname -- El Gordo (Spanish for "the fat one").
By measuring how much the cluster's gravity warps images of galaxies in the distant background, a team of astronomers has calculated the cluster's mass to be as much as 3 million billion times the mass of our sun. Hubble data show the galaxy cluster, which is 9.7 billion light-years away from Earth, is roughly 43 percent more massive than earlier estimates.
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Title: A highly elongated prominent lens at z=0.87: first strong lensing analysis of El Gordo
Authors: Adi Zitrin, Felipe Menanteau, John P. Hughes, Dan Coe, L. Felipe Barrientos, Leopoldo Infante, Rachel Mandelbaum

We present the first strong-lensing (SL) analysis of the galaxy cluster ACT-CL J0102-4915 (El Gordo), in recent HST/ACS images, revealing a prominent strong lens at a redshift of z=0.87. This finding adds to the already-established unique properties of El Gordo: it is the most massive, hot, X-ray luminous, and bright Sunyaev-Zeldovich effect cluster at z\gtrsim0.6, and the only 'bullet'-like merging cluster known at these redshifts. The lens consists of two merging massive clumps, where for a source redshift of z_{s}~2 each clump exhibits only a small, separate critical area, with a total area of 0.69±0.11\sq\arcmin over the two clumps. For a higher source redshift, z_{s}~4, the critical curves of the two clumps merge together into one bigger and very elongated lens (axis ratio \simeq5.5), enclosing an effective area of 1.44±0.22\sq\arcmin. The critical curves continue expanding with increasing redshift so that for high-redshift sources (z_{s}\gtrsim9) they enclose an area of ~1.91±0.30\sq\arcmin (effective \theta_{e}\simeq46.8±3.7\arcsec) and a mass of 6.25±1.06 x 10^{14}solar masses. According to our model, the area of high magnification (µ>10) for such high redshift sources is \simeq0.95\sq\arcmin, and the area with µ>5 is \simeq1.92\sq\arcmin, making El Gordo a compelling target for studying the high-redshift Universe. We obtain a strong lower limit on the total mass of El Gordo, \gtrsim1.7 x 10^{15} solar masses from the SL regime alone, suggesting a total mass of, roughly, M_{200}~2.3 x 10^{15} solar masses. The presented mass model could be improved with future HST imaging.

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'El Gordo' is largest distant galaxy cluster ever seen

The largest distant galaxy cluster has been spotted by astronomers using a telescope in Chile.
Galaxy clusters are the largest stable structures in our Universe.
Seven billion light years away and with two million billion times the mass of our Sun, the cluster was nicknamed "El Gordo" - "the Fat One" in Spanish.
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El Gordo - A "Fat" Distant Galaxy Cluster

eso1203a.jpg

An extremely hot, massive young galaxy cluster - the largest ever seen in the distant Universe - has been studied by an international team using ESO's Very Large Telescope (VLT) in the Atacama Desert in Chile along with NASA's Chandra X-ray Observatory and the Atacama Cosmology Telescope. The new results are being announced on 10 January 2012 at the 219th meeting of the American Astronomical Society in Austin, Texas.
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NASA's Chandra Finds Largest Galaxy Cluster in Early Universe

An exceptional galaxy cluster, the largest seen in the distant universe, has been found using NASA's Chandra X-ray Observatory and the National Science Foundation-funded Atacama Cosmology Telescope (ACT) in Chile.
Officially known as ACT-CL J0102-4915, the galaxy cluster has been nicknamed "El Gordo" ("the big one" or "the fat one" in Spanish) by the researchers who discovered it. The name, in a nod to the Chilean connection, describes just one of the remarkable qualities of the cluster, which is located more than 7 billion light years from Earth. This large distance means it is being observed at a young age.
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Title: The Atacama Cosmology Telescope: ACT-CL J0102-4215 "El Gordo," a Massive Merging Cluster at Redshift 0.87
Authors: Felipe Menanteau, John P. Hughes, Cristobal Sifon, Matt Hilton, Jorge Gonzalez, Leopoldo Infante, L. Felipe Barrientos, Andrew J. Baker, Sudeep Das, Mark J. Devlin, Joanna Dunkley, Adam D. Hincks, Arthur Kosowsky, Danica Mardsen, Tobias A. Marriage, Kavilan Moodley, Michael D. Niemack, Lyman A. Page, Erik D. Reese, Neelima Sehgal, Jon Sievers, David N. Spergel, Suzanne T. Staggs, Edward Wollack

We present a detailed analysis from new multi-wavelength observations of the exceptional galaxy cluster ACT-CL J0102-4915, likely the most massive, hottest, most X-ray luminous and brightest Sunyaev-Zel'dovich(SZ) effect cluster known at redshifts greater than 0.6. The Atacama Cosmology Telescope collaboration discovered it as the most significant SZ decrement in a sky survey area of 755 square degrees. Our VLT/FORS2 spectra of 89 member galaxies yield a cluster redshift, z=0.870, and velocity dispersion, sigma=132±106 km/s. Our Chandra observations reveal a hot and X-ray luminous system with an integrated temperature of Tx=14.5±0.1 keV and 0.5-2.0 keV band luminosity of Lx=(2.19±0.11) x 10^45 h_70^-2 erg/s. We obtain several statistically consistent cluster mass estimates; using empirical mass scaling relations with velocity dispersion, X-ray Yx, and integrated SZ distortion, we estimate a cluster mass of M_200=(2.16±0.32)x10^15 M_sun/h_70. The Chandra and VLT/FORS2 optical data also reveal that ACT-CL J0102-4915 is undergoing a major merger between components with a mass ratio of approximately 2 to 1. The X-ray data show significant temperature variations from a low of 6.6±0.7 keV at the merging low-entropy, high metallicity, cool core to a high of 22±6 keV. We also see a wake in the X-ray surface brightness and deprojected gas density caused by the passage of one cluster through the other from which we estimate a merger speed of around 1300 km/s for an assumed merger timescale of 1 Gyr. ACT-CL J0102-4915 is possibly a high-redshift analogy of the famous Bullet Cluster. Such a massive cluster at this redshift is rare, although consistent with the standard Lambda-CDM cosmology in the lower part of its allowed mass range. Massive, high-redshift mergers like ACT-CL J0102-4915 are unlikely to be reproduced in the current generation of numerical N-body cosmological simulations.

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