Resolving the Internal Structure of Circum-Galactic Medium using
  Gravitationally Lensed Quasars
  We study the internal structure of the Circum-Galactic Medium (CGM), using 29
spectra of 13 gravitationally lensed quasars with image separation angles of a
few arcseconds, which correspond to 100 pc to 10 kpc in physical distances.
After separating metal absorption lines detected in the spectra into high-ions
with ionization parameter (IP) $>$ 40 eV and low-ions with IP $<$ 20 eV, we
find that i) the fraction of absorption lines that are detected in only one of
the lensed images is larger for low-ions ($\sim$16%) than high-ions ($\sim$2%),
ii) the fractional difference of equivalent widths ($EW$s) between the lensed
images is almost same (${\rm d}EW$ $\sim$ 0.2) for both groups although the
low-ions have a slightly larger variation, and iii) weak low-ion absorbers tend
to have larger ${\rm d}EW$ compared to weak high-ion absorbers. We construct
simple models to reproduce these observed properties and investigate the
distribution of physical quantities such as size and location of absorbers,
using some free parameters. Our best models for absorbers with high-ions and
low-ions suggest that i) an overall size of the CGM is at least $\sim$ 500 kpc,
ii) a size of spherical clumpy cloud is $\sim$ 1 kpc or smaller, and iii) only
high-ion absorbers can have diffusely distributed homogeneous component
throughout the CGM. We infer that a high ionization absorber distributes almost
homogeneously with a small-scale internal fluctuation, while a low ionization
absorber consists of a large number of small-scale clouds in the diffusely
distributed higher ionized region. This is the first result to investigate the
internal small-scale structure of the CGM, based on the large number of
gravitationally lensed quasar spectra.
