  The circumgalactic medium (CGM) serves as a baryon reservoir that connects
galaxies to the intergalactic medium and fuels star formation. The spatial
distribution of the metal-enriched cool CGM has not yet been directly revealed
at cosmic noon (z~2-4), as bright emission lines at these redshifts are not
covered by optical integral field units. To remedy this situation, we aim for
the first-ever detections and exploration of extended SiII* emission
(low-ionization state, LIS), referred to as ``SiII* halos'', at redshifts
ranging from z=2 to 4 as a means to trace the metal-enriched cool CGM. We use a
sample of 39 galaxies with systemic redshifts of z=2.1-3.9 measured with the
[CIII] doublet in the MUSE Hubble Ultra Deep Field catalog, which contains
integration times spanning from ~30 to 140 hours. We search for extended
SiII*1265, 1309, 1533 emission (fluorescent lines) around individual galaxies.
We also stack a subsample of 14 UV-bright galaxies. We report five individual
detections of SiII*1533 halos. We also confirm the presence of SiII*1533 halos
in stacks for the subsample containing UV-bright sources. The other lines do
not show secure detections of extended emission in either individual or
stacking analyses. These detections may imply that the presence of
metal-enriched CGM is a common characteristic for UV-bright galaxies. To
investigate whether the origin of SiII* is continuum pumping as suggested in
previous studies, we check the consistency of the equivalent width (EW) of
SiII* emission and the EW of SiII absorption for the individual halo object
with the most reliable detection. We confirm the equivalence, suggesting that
photon conservation works for this object and pointing toward continuum pumping
as the source of SiII*. We also investigate SiII* lines in a RAMSES-RT zoom-in
simulation including continuum pumping and find ubiquitous presence of extended
halos.
