科研之友
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摘要
The frequency and effects of multiple weak deflections in galaxy-galaxy lensing are investigated via Monte Carlo simulations. The lenses in the simulations are galaxies with known redshifts and known rest-frame blue luminosities. The frequency of multiple deflections above a given threshold shear value is quantified for discrete source redshifts, as well as for a set of sources that are broadly distributed in redshift space. In general, the closest lens in projection on the sky is not the only lens for a given source. In addition, similar to 50% of the time the closest lens is not the most important lens for a given source. Compared to a naive single-deflection calculation in which only the lensing due to the closest weak lens is considered, a full multiple-deflection calculation yields a higher net shear for individual sources, as well as a higher mean tangential shear around the lens centers. The full multiple-deflection calculation also shows that galaxy-galaxy lensing may contribute a substantial amount to cosmic shear on small angular scales. The degree to which galaxy-galaxy lensing contributes to the small-scale cosmic shear is, however, quite sensitive to the mass adopted for the halos of L(B)* galaxies. Changing the halo mass by a factor of similar to 2.5 changes the contribution of galaxy-galaxy lensing to the cosmic shear by a factor of similar to 3 on scales of theta similar to 1'. The contribution of galaxy-galaxy lensing to cosmic shear decreases rapidly with angular scale and extrapolates to zero at theta similar to 5'. This last result is roughly independent of the halo mass and suggests that for scales theta greater than or similar to 5', cosmic shear is insensitive to the details of the gravitational potentials of large galaxies.
- 出版日期2010-4-10
