The MUSE Hubble Ultra Deep Field Survey. IV. Global properties of CIII] emitters

Abstract

The CIII] 1907, 1909 emission doublet has been proposed as an alternative to Lyman- 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 CIII]-emitting galaxies beyond z 1:5 using 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 2 10􀀀17 erg s􀀀1 cm􀀀2 in the HDFS and 7 10􀀀18 erg s􀀀1 cm􀀀2 in the UDF. The rest-frame equivalent widths range from 2 to 19 Å. 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 ( 1 10􀀀18 erg s􀀀1 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 Å, the so-called extreme emission line galaxies, have detections of CIII] 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.