Spectroscopic Confirmation of an Ultra Massive and Compact Galaxy at z=3.35: A Detailed Look at an Early Progenitor of Local Most Massive Ellipticals

Understand

We present the first spectroscopic confirmation of an ultra-massive galaxy at redshift z>3 using data from Keck-NIRSPEC, VLT-Xshooter, and GTC-Osiris.

• We detect strong [OIII] and Ly$\alpha$ emission, and weak [OII], CIV, and HeII, placing C1-23152 at a spectroscopic redshift of $z_{spec}$=3.351.
• The modeling of the emission-line corrected spectral energy distribution results in a best-fit stellar mass of $M_{*}=3.1^{+0.6}_{-0.7}\times10^{11} M_{\odot}$, a star-formation rate of <7 $M_{\odot} yr^{-1}$, and negligible dust extinction.
• The stars appear to have formed in a short intense burst ~300-500 Myr prior to the observation epoch, setting the formation redshift of this galaxy at z~4.1.