Title: Search for CDM subhalos by mid-infrared imaging of lensed QSOs
Author(s): Minezaki, T., Chiba, M., Inoue, K. T., Kashikawa, N., Kataza, H., & Packham, C.
Abstract:
We report our project on mid-infrared imaging of quadruply lensed
QSOs, in order to set constraints on the abundance of dark matter
subhalos in foreground lensing galaxies. This is motivated by the
prediction of the cold dark matter (CDM) scenario, suggesting
the presence of a large number of subhalos in a galaxy-sized halo.
In this study, mid-infrared observations of lensed images and their
anomalous flux ratios provide us with advantageous perspectives.
Firstly, mid-infrared flux is free from dust extinction effects
which modify lensed flux. Secondly, mid-infrared flux is free from
microlensing effects: the flux originated from an extended dust torus
of a QSO is selectively modified by CDM subhalos whereas it is
unaffected by stellar populations. Finally, the mid-infrared flux
ratio enables us to place a useful limit on the mass of CDM subhalos,
because the source size can be quantitatively estimated from the QSO
luminosity, based on dust reverberation observations.

We have conducted systematic mid-infrared imaging of bright
quadruple lenses using both Subaru/COMICS and Gemini-South/T-ReCS.
Our study demonstrates fruitful cooperation between Subaru and Gemini
telescopes (Chiba et al. 2005; Minezaki et al. 2009).