  The C III] 1907,1909 emission doublet has been proposed as an alternative to
Lyman-alpha in redshift confirmations of galaxies at z > 6 since it is not
attenuated by the largely neutral intergalactic medium at these redshifts and
is believed to be strong in the young, vigorously star-forming galaxies present
at these early cosmic times. We present a statistical sample of 17 C
III]-emitting galaxies beyond z~1.5 using 30 hour deep VLT/MUSE integral field
spectroscopy covering 2 square arcminutes in the Hubble Deep Field South (HDFS)
and Ultra Deep Field (UDF), achieving C III] sensitivities of ~2e-17 erg/s/cm^2
in the HDFS and ~7e-18 erg/s/cm^2 in the UDF. The rest-frame equivalent widths
range from 2 to 19 Angstroms. These 17 galaxies represent ~3% of the total
sample of galaxies found between 1.5 < z < 4. They also show elevated star
formation rates, lower dust attenuation, and younger mass-weighted ages than
the general population of galaxies at the same redshifts. Combined with deep
slitless grism spectroscopy from the HST/WFC3 in the UDF, we can tie the
rest-frame ultraviolet C III] emission to rest-frame optical emission lines,
namely [O III] 5007, finding a strong correlation between the two. Down to the
flux limits that we observe (~1e-18 erg/s/cm^2 with the grism data in the UDF),
all objects with a rest-frame [O III] 4959,5007 equivalent width in excess of
250 Angstroms, the so-called Extreme Emission Line Galaxies, have detections of
C III] in our MUSE data. More detailed studies of the C III]-emitting
population at these intermediate redshifts will be crucial to understand the
physical conditions in galaxies at early cosmic times and to determine the
utility of C III] as a redshift tracer.
