### [1009.3884] Too big, too early? Multiple High-Redshift Gala

Posted:

**September 22 2010**The authors consider 15 massive clusters observed at redshifts >1. In the vanilla [tex]\Lambda[/tex]CDM model, you don't expect a lot of massive clusters early on. The authors report a probability of [tex]3\times10^{-4}[/tex] for having so many so massive clusters in the observed region.

The authors focus on the influence of non-Gaussianity: the probability of massive clusters rises with [tex]f_{NL}[/tex], and the authors find that for [tex]f_{NL}=550[/tex] the probability rises to one. Personally, I am not that much into in large non-Gaussianity, but the observation of the discrepancy is interesting. I would imagine that for example slower expansion at high redshifts would increase the number of clusters; one could check whether the required change is consistent with the supernova data.

As a caveat, the authors note that the observations would be consistent with the standard picture with no non-Gaussianity if the cluster masses are over-estimated by 1.5[tex]\sigma[/tex], which doesn't seem like a lot to me. I am not too familiar with this, but I recall there has been controversy over the cluster abundance and the X-ray mass determinations before ( http://cosmocoffee.info/viewtopic.php?t=296&highlight= ; see also http://arxiv.org/abs/1006.3859).

The authors focus on the influence of non-Gaussianity: the probability of massive clusters rises with [tex]f_{NL}[/tex], and the authors find that for [tex]f_{NL}=550[/tex] the probability rises to one. Personally, I am not that much into in large non-Gaussianity, but the observation of the discrepancy is interesting. I would imagine that for example slower expansion at high redshifts would increase the number of clusters; one could check whether the required change is consistent with the supernova data.

As a caveat, the authors note that the observations would be consistent with the standard picture with no non-Gaussianity if the cluster masses are over-estimated by 1.5[tex]\sigma[/tex], which doesn't seem like a lot to me. I am not too familiar with this, but I recall there has been controversy over the cluster abundance and the X-ray mass determinations before ( http://cosmocoffee.info/viewtopic.php?t=296&highlight= ; see also http://arxiv.org/abs/1006.3859).