A massive quiescent galaxy in a group environment at $z=4.53$

Understand

We report on the spectroscopic confirmation of a massive quiescent galaxy at $z_\mathrm{spec}=4.53$ in the COSMOS field.

• The object was first identified as a galaxy with suppressed star formation at $z_\mathrm{phot}\sim4.65$ from the COSMOS2020 catalog.
• The follow-up spectroscopy with Keck/MOSFIRE in the $K$-band reveals faint [OII] emission and the Balmer break, indicative of evolved stellar populations.
• We perform the spectral energy distribution fitting using photometry and spectrum to infer physical properties.