Projection effects in cluster mass estimates: the case of MS2137-23

Free access article

Issue		A&A Volume 443, Number 3, December I 2005


Page(s)		793 - 804
Section		Cosmology (including clusters of galaxies)
DOI		http://dx.doi.org/10.1051/0004-6361:20053166

A&A 443, 793-804 (2005)
DOI: 10.1051/0004-6361:20053166

Projection effects in cluster mass estimates: the case of MS2137-23

R. Gavazzi^{1, 2}

¹ Institut d'Astrophysique de Paris, UMR 7095, 98bis Bd Arago, 75014 Paris, France
e-mail: rgavazzi@ast.obs-mip.fr
² Laboratoire d'Astrophysique, OMP, UMR 5572, 14 Av. Edouard Belin, 31400 Toulouse, France

(Received 31 March 2005 / Accepted 28 June 2005 )

Abstract
We revisit the mass properties of the lensing cluster of galaxies MS2137-23 and assess the mutual agreement between cluster mass estimates based on strong/weak lensing, X-rays and stellar dynamics. We perform a thorough elliptical lens modelling using arcs and their counter-images in the range $20\lesssim R\lesssim100$ kpc and weak lensing ( $100\lesssim R\lesssim1000$ kpc). We confirm that the dark matter distribution is consistent with an NFW profile (Navarro et al., 1997, ApJ, 490, 493) with high concentration $c\sim11.7\pm0.6$ . We further analyse stellar kinematics data with a detailed modelling of the line-of-sight velocity distribution (LOSVD) of stars in the cD galaxy and quantify the small bias due to the non-Gaussian shape of the LOSVD. After correction, the NFW lens model is unable to properly fit kinematical data and is a factor of ~2 more massive than suggested by X-rays analysis. The discrepancy between projected (lensing) and tridimensional (X-rays, dynamics) mass estimates is studied by assuming prolate (triaxial) halos with the major axis oriented toward the line-of-sight. This model well explains the high concentration and the misalignement between stellar and dark matter components $(\Delta \psi \sim 13^\circ)$ . We then calculate the systematic and statistical uncertainties in the relative normalization between the cylindric M₂(<r) and spherical M₃(<r) mass estimates for triaxial halos. These uncertainties prevent any attempt to couple 2D and 3D constraints without undertaking a complete tridimensional analysis. Such asphericity/projection effects should be a major concern for comparisons between lensing and X-rays/dynamics mass estimates.

Key words: cosmology: dark matter -- galaxies: clusters: individual: MS2137 -- galaxies: elliptical and lenticular, cD -- gravitational lensing -- galaxies: kinematics and dynamics -- galaxies: clusters: general

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