  We present mid-infrared imaging at 11.7 mu m for the quadruple lens systems,
PG1115+080 and B1422+231, using the cooled mid-infrared camera and spectrometer
(COMICS) attached on the Subaru telescope. These lensed QSOs are characterized
by their anomalous optical and radio flux ratios as obtained for (A1, A2)
images of PG1115+080 and (A, B, C) images of B1422+231, respectively, i.e.,
such flux ratios are hardly reproduced by lens models with smooth mass
distribution. Our mid-infrared observations for these images have revealed that
the mid-infrared flux ratio A2/A1 of PG1115+080 is virtually consistent with
smooth lens models (but inconsistent with the optical flux ratio), whereas for
B1422+231, the mid-infrared flux ratios among (A, B, C) are in good agreement
with the radio flux ratios. We also identify a clear infrared bump in the
spectral energy distributions of these QSOs, thereby indicating that the
observed mid-infrared fluxes originate from a hot dust torus around a QSO
nucleus. Based on the size estimate of the dust torus, we place limits on the
mass of a substructure in these lens systems, causing the anomalous optical or
radio flux ratios. For PG1115+080, the mass of a substructure inside an
Einstein radius, M_E, is < 16 Msun, corresponding to either a star or a
low-mass CDM subhalo having the mass of M_{100}^{SIS} < 2.2 * 10^4 Msun inside
radius of 100 pc if modeled as a singular isothermal sphere (SIS). For
B1422+231, we obtain M_E > 209 Msun, indicating that a CDM subhalo is more
likely, having the mass of M_{100}^{SIS} > 7.4 * 10^4 Msun

Astrophysics