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The COSMOS density field : a reconstruction using both weak lensing and galaxy distributions.

Amara, A. and Lilly, S. and Kovac, K. and Rhodes, J. and Massey, R. and Zamorani, G. and Carollo, C.M. and Contini, T. and Kneib, J.-P. and Le Fevre, O. and Mainieri, V. and Renzini, A. and Scodeggio, M. and Bardelli, S. and Bolzonella, M. and Bongiorno, A. and Caputi, K. and Cucciati, O. and de la Torre, S. and de Ravel, L. and Franzetti, P. and Garilli, B. and Iovino, A. and Kampczyk, P. and Knobel, C. and Lamareille, F. and Le Borgne, J.-F. and Le Brun, V. and Maier, C. and Mignoli, M. and Pello, R. and Peng, Y. and Perez Montero, E. and Presotto, V. and Silverman, J. and Tanaka, M. and Tasca, L. and Tresse, L. and Vergani, D. and Zucca, E. and Barnes, L. and Bordoloi, R. and Cappi, A. and Cimatti, A. and Coppa, G. and Koekoemoer, A. and Lopez-Sanjuan, C. and McCracken, H.J. and Moresco, M. and Nair, P. and Pozzetti, L. and Welikala, N. (2012) 'The COSMOS density field : a reconstruction using both weak lensing and galaxy distributions.', Monthly notices of the Royal Astronomical Society., 424 (1). pp. 553-563.


The COSMOS field has been the subject of a wide range of observations, with a number of studies focusing on reconstructing the 3D dark matter density field. Typically, these studies have focused on one given method or tracer. In this paper, we reconstruct the distribution of mass in the COSMOS field out to a redshift z= 1 by combining Hubble Space Telescope weak lensing measurements with zCOSMOS spectroscopic measurements of galaxy clustering. The distribution of galaxies traces the distribution of mass with high resolution (particularly in redshift, which is not possible with lensing), and the lensing data empirically calibrates the mass normalization (bypassing the need for theoretical models). Two steps are needed to convert a galaxy survey into a density field. The first step is to create a smooth field from the galaxy positions, which is a point field. We investigate four possible methods for this: (i) Gaussian smoothing, (ii) convolution with truncated isothermal sphere, (iii) fifth nearest neighbour smoothing and (iv) a multiscale entropy method. The second step is to rescale this density field using a bias prescription. We calculate the optimal bias scaling for each method by comparing predictions from the smoothed density field with the measured weak lensing data, on a galaxy-by-galaxy basis. In general, we find scale-independent bias for all the smoothing schemes, to a precision of 10 per cent. For the nearest neighbour smoothing case, we find the bias to be 2.51 ± 0.25. We also find evidence for a strongly evolving bias, increasing by a factor of ∼3.5 between redshifts 0 < z < 0.8. We believe this strong evolution can be explained by the fact that we use a flux limited sample to build the density field.

Item Type:Article
Keywords:Dark matter, Large-scale structure of Universe.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:17 February 2015
Date of first online publication:July 2012
Date first made open access:No date available

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