The MUSE &ITHubble&IT Ultra Deep Field Survey IV. Global properties of C III] emitters

The C III] lambda lambda 1907, 1909 emission doublet has been proposed as an alternative to Lyman-alpha in redshift confirmations of galaxies at z greater than or similar to 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 similar to 1.5 using similar to 30 h 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 similar to 2 x 10(-17) erg s(-1) cm(-2) in the HDFS and similar to 7 x 10(-18) erg s(-1) cm(-2) in the UDF. The rest-frame equivalent widths range from 2 to 19 angstrom. These 17 galaxies represent similar to 3% of the total sample of galaxies found between 1.5 less than or similar to z less than or similar to 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] lambda 5007, finding a strong correlation between the two. Down to the flux limits that we observe (similar to 1 x 10(-18) erg s(-1) cm(-2) with the grism data in the UDF), all objects with a rest-frame [O III] lambda lambda 4959, 5007 equivalent width in excess of 250 angstrom, 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.