Implications for Primordial Non-Gaussianity (f_NL) from weak lensing masses of high-z galaxy clusters

Abstract

The recent weak lensing measurement of the dark matter mass of the high-redshift galaxy cluster XMMUJ2235.3-2557 of (8.5 +- 1.7) x 10^{14} Msun at z=1.4, indicates that, if the cluster is assumed to be the result of the collapse of dark matter in a primordial gaussian field in the standard LCDM model, then its abundance should be < 0.002 clusters in the observed area. Here we investigate how to boost the probability of XMMUJ2235.3-2557 in particular resorting to deviations from Gaussian initial conditions. We show that this abundance can be boosted by factors > 3-10 if the non-Gaussianity parameter f^local_NL is in the range 150-200. This value is comparable to the limit for f_NL obtained by current constraints from the CMB. We conclude that mass determination of high-redshift, massive clusters can offer a complementary probe of primordial non-gaussianity.

Figures (1)

• Figure 1: Enhancement factor ${\cal R}_{NG}$ of the number of rare objects for different values of the dark matter mass of the galaxy cluster. The lines correspond to different values of $f_{NL}$. The upper lines are for a collapse redshift of $z_f=2$ and the lower lines for $z_f=1.4$. The shaded area is the range for the weak lensing mass estimate of the clusters XMMUJ2235.3-2557. Note that for the quoted values of $f^{local}_{NL}$ it is possible to obtain enhancements of order $10$ in the cluster number abundance. This enhancement brings the expected abundance of such massive clusters in better agreement with the observations. Note that for masses above the estimated central value ($8.5 \times 10^{14}$ M$_{\odot}$) one expects to find zero such objects in the whole sky (one expects 7 objects in the whole sky at the lowest value of the mass estimate) which emphasizes the need of an enhancement as the one provided by primordial non-gaussianity studied here.