Thursday, July 18, 2013

1307.4399 (Masahiro Takada et al.)

Joint likelihood function of cluster number counts and weak lensing power spectrum    [PDF]

Masahiro Takada, David N. Spergel
A coherent over- or under-density contrast across a finite survey volume causes an upward- or downward- fluctuation in the number of halos. This fluctuation in halo number adds a significant co-variant scatter in the observed amplitudes of weak lensing power spectrum at nonlinear, small scales. Because of this covariance, the amount of information that can be extracted from a measurement of the weak lensing power spectrum is significantly smaller than naive estimates. In this paper, we show that by measuring both the number counts of clusters and the power spectrum in the same survey region, we can mitigate this loss of information and significantly enhance the scientific return from the upcoming surveys. First, using the halo model approach, we derive the joint likelihood function of the halo number counts and the weak lensing power spectrum, taking into account the super-sample co-variance effect on the two observables. We show that the analytical model matches the distributions measured from 1000 realizations for a LCDM model. Then we develop a method of combining the observed number counts of massive halos with a measurement of the weak lensing power spectrum, in order to suppress or correct for the super-sample variance effect. Adding the observed number counts of massive halos with M> 10^{14} Ms/h can significantly improve the information content of weak lensing power spectrum, almost recovering the Gaussian information of the initial density field up to lmax~1000. When combined with the halo number counts for M > 3 or 1 x 10^{14} Ms/h, the improvement is up to a factor of 1.4 or 2 at angular modes of lmax~1000-2000, equivalent to a factor 2 or 4 times larger survey volume, compared to the power spectrum measurement without the Gaussianization method. The improvements are larger for surveys with higher number densities of galaxies.
View original:

No comments:

Post a Comment