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 normalisation ( 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 muliti-scale 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 \% .
For the nearest neighbour smoothing case , we find the bias to be 2.51 \pm 0.25 .
We also find evidence for a strongly evolving bias , increasing by a factor of \sim 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 .