Enhanced star formation and metallicity deficit in the USS 1558−003 forming protocluster at z = 2.53

Abstract

ABSTRACT We use K-band multi-object near-infrared spectroscopy with Keck/MOSFIRE to search for environmental imprints on the gas properties of 27 narrow-band selected H α emitters (HAEs) across the three major clumps of the assembling USS1558−003 protocluster at z = 2.53. We target the H α and [N ii]λ6584 emission lines to obtain star formation rates (SFR) and gas-phase oxygen abundances for our sources, confirming the membership of 23 objects. HAEs belonging to this protocluster display enhanced SFRs with respect to the main sequence of star formation at the same cosmic epoch. This effect is more prominent for low-mass galaxies ($\mathrm{\log \mathit{ M}_*/M_\odot \lt 10.0}$), which may be experiencing a vigorous phase of mass assembly shortly after they were formed. We compute the individual and stacked gas-phase metallicities for our sources finding a metallicity deficit for low-mass objects when compared against the field mass–metallicity relation and the massive Spiderweb protocluster at z = 2.16. These results suggest that HAEs within USS1558−003 may be less evolved than those in the Spiderweb protocluster. Finally, we explore the gas metallicity–gas fraction relation for a small sample of five galaxies with CO(3–2) molecular gas information. Assuming our objects are in equilibrium, we obtain a relatively wide range of mass loading factors (λ = 0.5–2) matching field samples at the cosmic noon but in contrast with our previous results in the Spiderweb protocluster. We speculate that these discrepancies between protoclusters may be (partly) driven by differences in their current dynamical and mass assembly stages, hinting at the co-evolution of protoclusters and their galaxy populations at 2 < z < 3.