CIV detected in GLASS spectra of lensed system at z=6.11


Schmidt et al. (2017) present the detection of the CIV emission line in multiple images of a quintuply imaged Lyα emitter at z=6.11. The lensed object behind RXJ2248 was first identified by Monna et al. (2014) and multiple components of the system have since then been spectroscopically confirmed via Lyα emission. The rest-frame stack of the GLASS spectra from the multiple components of the lensed system shown in the figure clearly shows the detection of CIV and the confirmation of the Lyα emission, improving the signal-to-noise of the CIV (and Lyα) detections in the individual spectra of the individual components of the lensed system. The stacked spectra indicate an equivalent width of Lyα and CIV of 68±6Å and 24±4Å, respectively. Thanks to the broad wavelength coverage of the near-infrared GLASS spectra, the detections of Lyα and CIV are accompanied by flux limits on other rest-frame UV lines including HeII, OIII and CIII which were not detected in the GLASS spectra.

From updated photometric measurements including deep Hubble Frontier Fields imaging, archival imaging, and Spitzer observations and the corresponding fits of the spectral energy distribution (SED), Schmidt et al. (2017) estimate the galaxy to have a mass of roughly 10^9 Msun and a star formation rate of approximately 10 Msun/yr (both corrected for lensing magnification) in fair agreement with previous estimates. The photometry also reveals a young stellar population with an age of ~50 Myrs and a system with low dust content (E(B-V) ~ 0.05).

Rest-frame UV emission lines are very useful beacons for studying the physical properties of galaxies and provide information beyond what photometry and SED fits provide. Hence, the detection of CIV as well as the limits on the non-detections of the other rest-frame UV lines provide an opportunity to study the physical properties of the z=6.11 Lyα emitter. In particular, Schmidt et al. (2017) compare the rest-frame UV emission line flux ratios obtained from the GLASS spectra, to the predictions from recent photoionization models of AGN and star formatting galaxies from Feltre et al. (2016) and Gutkin et al. (2016). Such a comparison can potentially constraint the ionization parameter (logU) and the gas-phase metallicity of the galaxy (Zgas). The flux limits from the GLASS data show that the ionizing radiation powering the CIV emission is most likely from star formation as opposed to AGN activity, but are not strong enough to give tight constraints on the logU and Zgas.

For more details please refer to Schmidt et al. (2017)