http://arxiv.org/abs/1402.1496
Strong gravitational lenses can be used to detect low mass subhalos, based on deviations in image fluxes and positions from what can be achieved with a smooth mass distribution. So far, this method has been limited by the small number of suitable (radio-loud) systems which can be analysed for the presence of substructure. Using the gravitational lens B1422+231 as a case study, we demonstrate that adaptive optics integral field spectroscopy can also be used to detect dark substructures. We analyse data obtained with OSIRIS on the Keck Telescope, using a Bayesian method that accounts for uncertainties relating to the point spread function and image positions in the separate exposures. The narrow [OIII] fluxes measured for the lensed images show a significant deviation from what would be expected in a smooth mass distribution, consistent the presence of a perturbing low mass halo. Detailed lens modelling shows that image fluxes and positions are well reproduced by a model with a single subhalo in addition to the main halo. The inferred mass of the subhalo depends on the subhalo mass density profile: the 68 \% confidence interval for the perturber mass within 600 pc are: 8.2$^{+0.6}_{-0.8}$, 8.2$^{+0.6}_{-1}$ and 7.6$^{+0.3}_{-0.3}$ Log_10[M_sub/M_sun] respectively for a singular isothermal sphere, a pseudo-Jaffe, and a NFW mass profile. This method can extend the study of flux ratio anomalies to virtually all quadruply imaged quasars, and therefore offers great potential to improve the determination of the subhalo mass function in the near future.
A. Nierenberg, T. Treu, S. Wright, et. al.
Mon, 10 Feb 14
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