* Astronomy

Title: CLASH: Precise New Constraints on the Mass Profile of Abell 2261
Authors: Dan Coe, Keiichi Umetsu, Adi Zitrin, Megan Donahue, Elinor Medezinski, Marc Postman, Mauricio Carrasco, Timo Anguita, Margaret J. Geller, Kenneth J. Rines, Antonaldo Diaferio, Michael J. Kurtz, Larry Bradley, Anton Koekemoer, Wei Zheng, Mario Nonino, Alberto Molino, Andisheh Mahdavi, Doron Lemze, Leopoldo Infante, Sara Ogaz, Peter Melchior, Ole Host, Holland Ford, Claudio Grillo, Piero Rosati, Yolanda Jiménez-Teja, John Moustakas, Tom Broadhurst, Begoña Ascaso, Ofer Lahav, Matthias Bartelmann, Narciso Benítez, Rychard Bouwens, Or Graur, Genevieve Graves, Saurabh Jha, Stephanie Jouvel, Daniel Kelson, Leonidas Moustakas, Dan Maoz, Massimo Meneghetti, Julian Merten, Adam Riess, Steve Rodney, Stella Seitz

We precisely constrain the inner mass profile of Abell 2261 (z=0.225) for the first time and determine this cluster is not "over-concentrated" as found previously, implying a formation time in agreement with {\Lambda}CDM expectations. These results are based on strong lensing analyses of new 16-band HST imaging obtained as part of the Cluster Lensing and Supernova survey with Hubble (CLASH). Combining this with revised weak lensing analyses of Subaru wide field imaging with 5-band Subaru + KPNO photometry, we place tight new constraints on the halo virial mass M_vir = 2.2±0.2 x 10^15 solar masses/h70 (within r ~ 3 Mpc/h70) and concentration c = 6.2 ±0.3 when assuming a spherical halo. This agrees broadly with average c(M,z) predictions from recent {\Lambda}CDM simulations which span 5 <~ <c> <~ 8. Our most significant systematic uncertainty is halo elongation along the line of sight. To estimate this, we also derive a mass profile based on archival Chandra X-ray observations and find it to be ~35% lower than our lensing-derived profile at r2500 ~ 600 kpc. Agreement can be achieved by a halo elongated with a ~2:1 axis ratio along our line of sight. For this elongated halo model, we find M_vir = 1.7±0.2 x 10^15 solar masses/h70 and c_vir = 4.6±0.2, placing rough lower limits on these values. The need for halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic errors in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec spectroscopic redshifts and find these tend to lower Mvir further by ~7% and increase cvir by ~5%.

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