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

The C III] λλ1907, 1909 emission doublet has been proposed as an alternative to Lyman-α 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 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] λ5007, 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] λλ4959, 5007 equivalent width in excess of 250 Å, 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.

Based on observations made with ESO telescopes at the La Silla Paranal Observatory under program IDs 60.A-9100(C), 094.A-2089(B), 095.A-0010(A), 096.A-0045(A), and 096.A-0045(B). This work is also based on observations made with the NASA/ESA Hubble Space Telescope, programs GO-12099 and 12177, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.