Confirmation of Planet-Mass Objects in Extragalactic Systems
  Quasar microlensing serves as a unique probe of discrete objects within
galaxies and galaxy clusters. Recent advancement of the technique shows that it
can constrain planet-scale objects beyond our native galaxy by studying their
induced microlensing signatures, the energy shift of emission lines originated
in the vicinity of the black hole of high redshift background quasars. We
employ this technique to exert effective constraints on the planet-mass object
distribution within two additional lens systems, Q J0158$-$4325 ($z_l = 0.317$)
and SDSS J1004+4112 ($z_l = 0.68$) using Chandra observations of the two
gravitationally-lensed quasars. The observed variations of the emission line
peak energy can be explained as microlensing of the FeK$\alpha$ emission region
induced by planet-mass microlenses. To corroborate this, we perform
microlensing simulations to determine the probability of a caustic transiting
the source region and compare this with the observed line shift rates. Our
analysis yields constraints on the sub-stellar population, with masses ranging
from Moon ($10^{-8} M_{\odot}$) to Jupiter ($10^{-3} M_{\odot}$) sized bodies,
within these galaxy or cluster scale structures, with total mass fractions of
$\sim 3\times10^{-4}$ and $\sim 1\times10^{-4}$ with respect to halo mass for Q
J0158$-$4325 and SDSS J1004+4112, respectively. Our analysis suggests that
unbound planet-mass objects are universal in galaxies, and we surmise the
objects to be either free-floating planets or primordial black holes. We
present the first-ever constraints on the sub-stellar mass distribution in the
intra-cluster light of a galaxy cluster. Our analysis yields the most stringent
limit for primordial black holes at the mass range.
