ZFIRE: Similar Stellar Growth in Hα-emitting Cluster and Field Galaxies at z ~ 2

Abstract

We compare galaxy scaling relations as a function of environment at z∼ 2 with our ZFIRE survey¹² where we have measured Hα fluxes for 90 star-forming galaxies selected from a mass-limited ({log}({M}_\star /{M}_⊙ )> 9) sample based on ZFOURGE.¹³ The cluster galaxies (37) are part of a confirmed system at z = 2.095 and the field galaxies (53) are at 1.9< z< 2.4; all are in the COSMOS legacy field. There is no statistical difference between Hα-emitting cluster and field populations when comparing their star formation rate (SFR), stellar mass ({M}_\star ), galaxy size ({r}_{eff}), SFR surface density (Σ({{H}}{α }_{star})), and stellar age distributions. The only difference is that at fixed stellar mass, the Hα-emitting cluster galaxies are {log}({r}_{eff}) ∼ 0.1 larger than in the field. Approximately 19% of the Hα emitters in the cluster and 26% in the field are IR-luminous ({L}_{IR} > 2 × 10¹¹ {L}_⊙ ). Because the luminous IR galaxies in our combined sample are ∼5 times more massive than the low-IR galaxies, their radii are ∼70% larger. To track stellar growth, we separate galaxies into those that lie above, on, or below the Hα star-forming main sequence (SFMS) using ΔSFR({M}_\star ) = ±0.2 dex. Galaxies above the SFMS (starbursts) tend to have higher Hα SFR surface densities and younger light-weighted stellar ages than galaxies below the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field at z∼ 2 are growing their stellar cores. Lastly, we compare to the (SFR-{M}_\star ) relation from Rhapsody-G cluster simulations and find that the predicted slope is nominally consistent with the observations. However, the predicted cluster SFRs tend to be too low by a factor of ∼2, which seems to be a common problem for simulations across environment.