Direct Detection of CDM Substructure

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  • 23 November 2001
Abstract
We devise a method to measure the abundance of satellite halos in gravitational lens galaxies, and apply our method to a sample of 7 lens systems. After using Monte Carlo simulations to verify the method, we find that substructure comprises f=0.02 (median, 0.006<f<0.07 at 90% confidence) of the mass of typical lens galaxies, in excellent agreement with predictions of CDM simulations. We estimate a characteristic critical radius for the satellites of 0.0001<b<0.006 arcsec (90% confidence). For a dn/dM ~ 1/M^2 (M_l < M < M_h) satellite mass function, the critical radius provides an estimate that the upper mass limit is 10^6 Msun < M_h < 10^9 Msun. Our measurement confirms a generic prediction of CDM models, and may obviate the need to invoke alternatives to CDM like warm dark matter or self-interacting dark matter.

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