RELICS: Spectroscopy of gravitationally-lensed z ≃ 2 reionization-era analogs and implications for CIII] detections at z > 6
Recent observations have revealed the presence of strong CIII] emission (EWCIII] > 20 Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to understand the nature of these line emitters, we have initiated a survey targeting CIII] emission in gravitationally-lensed reionization era analogs identified in HST imaging of clusters from the RELICS survey. Here we report initial results on four galaxies selected to have low stellar masses (2-8× 107 M☉) and J125-band flux excesses indicative of intense [OIII]+Hβ emission (EW[OIII] + Hβ=500-2000 Å), similar to what has been observed at z > 6. We detect CIII] emission in three of the four sources, with the CIII] EW reaching values seen in the reionization era (EWCIII] ≃ 17 - 22 Å) in the two sources with the strongest optical line emission (EW[OIII] + Hβ ≃ 2000 Å). We have obtained a Magellan/FIRE near-infrared spectrum of the strongest CIII] emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense CIII] and optical line emission for extremely young (2-3 Myr) and metal poor (0.06-0.08 Z☉) stellar populations, as would be expected after a substantial upturn in the SFR of a low mass galaxy. The sources in this survey are among the first for which CIII] has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using CIII] to measure redshifts of objects with IRAC excesses indicating EW[OIII] + Hβ ≃ 2000 Å, providing a method of spectroscopic confirmation independent of Lyα.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2020
- Galaxy evolution;
- Astrophysics - Astrophysics of Galaxies
- Accepted for publication in MNRAS