ar X iv : a st ro - p h / 03 09 73 8 v 1 2 6 Se p 20 03 Spectroscopic Gravitational Lensing and Limits on the Dark Matter Substructure in Q 2237 + 0305

Spatially resolved spectroscopic data from the CIRPASS integral field unit (IFU) on Gemini are used to measure the gravitational lensing of the 4–image quasar Q2237+0305 on different size scales. A method for measuring the substructure present in the lens using observations at multiple wavelengths is demonstrated to be very effective and independent of many of the degeneracies inherent in previous methods. The magnification ratios of the QSO’s narrow line region (NLR) and broad line region (BLR) are measured and found to be disagree with each other and with the published radio and mid-infrared magnification ratios. The disagreement between the BLR ratios and the radio/mid-infrared ratios is interpreted as microlensing by stars in the lens galaxy of the BLR. This implies that the mid-infrared emission region is larger than the BLR and the BLR is < ∼ 0.1 pc in size. We find a small difference in the shape of the Hβ line in image A when compared to the other images. We consider this difference too small and symmetric to be considered strong evidence for rotation or large scale infall in the Hβ emission region. The disagreement between the radio/mid-infrared ratios and the NLR ratios is interpreted as a signature of substructure on a larger scale, possibly the missing small scale structure predicted by the standard cold dark matter (CDM) model. Extensive lensing simulations are performed to obtain a lower limit on the amount of substructure that is required to cause this discrepancy as a function of its mass and the radial profile of the host lens. The substructure surface density is degenerate with the radial profile of the host lens, but if the expectations of the CDM model are taken into account certain radial profiles and substructure surface densities can be ruled out. A substructure mass scale as large as 10 M⊙ is strongly disfavored while 10 M⊙ is too small if the radio and mid-infrared emission regions have the expected sizes of ∼ 10 pc. The standard elliptical isothermal lens mass profile is not compatible with a substructure surface density of Σsub < 280 M⊙ pc−2 at the 95% confidence level. This is