3d Mapping of Cdm Substructure at Submillimeter Wavelengths

The Cold Dark Matter (CDM) structure formation model predicts that about 5-10 percent of a typical galactic halo mass ∼ 10M⊙is in substructures with a mass . 10M⊙. To directly detect such substructures, we propose to observe dust continuum emission from a strongly lensed QSO-host galaxy using a large submillimeter interferometer array with a high angular resolution ∼ 0.01arcsec such as the planned Atacama Large Submillimeter Array (ALMA). To assess their observational feasibility, we numerically simulate millilensing of an extended circular source by a CDM substructure modeled as a tidally truncated singular isothermal sphere (SIS) embedded in a typical QSO-galaxy lens system B1422+231 modeled as a singular isothermal ellipsoid (SIE) with an external constant shear and a constant convergence. Assuming an angular resolution 0.01arcsec, we find that angular position of ∼ 10M⊙ substructures at several kpc from the center of the macrolens halo can be directly measured if the size of dust continuum emission region and the gradient of surface brightness at the position of the perturber are sufficiently large. From astrometric shift on scale of a few 10 mas of an image perturbed by a subhalo with respect to an unperturbed macrolensed image, we can break degeneracy between a subhalo mass and a distance provided that macrolensing parameters are determined from positions and fluxes of multiple images. Subject headings: cosmology: theory – dark matter – gravitational lensing – large-scale structure of universe