求翻译：Based on the group catalog (GC) of the SDSS-DR4 [Yang et al., ApJ 671, 153 (2007)] we implemented a halo-based density field reconstruction method introduced by [Wang et al., MNRAS 394, 398 (2009)]. The method uses the mass distribution in and around dark matter structures computed from cosmological simulations to map the cosmic mass distribution. This approach enables us to make reconstructions of the density field avoiding the use of arbitrary smoothing functions and including information about the mass distribution in the environment of halos. We present the results of our reconstruction as well as the identification of different environments. The reconstructed density field will be further used in the investigation of environmental dependence of galaxy properties.是什么意思？

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