ZFIRE: GALAXY CLUSTER KINEMATICS, Hα STAR FORMATION RATES, AND GAS PHASE METALLICITIES OF XMM-LSS J02182-05102 AT ${z}_{\mathrm{cl}}=1.6233$

Abstract

We spectroscopically survey the galaxy cluster XMM-LSS J02182-05102 (hereafter IRC 0218) using LRIS (optical) and MOSFIRE (near-infrared) on Keck I as part of the ZFIRE survey. IRC 0218 has a narrow redshift range of $1.612\;\lt \;$ ${z}_{\mathrm{spec}}$ $\;\lt \;1.635$ defined by 33 members of which 20 are at R${}_{\mathrm{proj}}$ $\;\lt \;1$ Mpc. The cluster redshift and velocity dispersion are ${z}_{\mathrm{cl}}=1.6233\pm 0.0003$ and ${\sigma }_{\mathrm{cl}}=254\pm 50$ km s−1. We reach NIR line sensitivities of ~0.3 × 10−17 erg s−1 cm−2 that, combined with multi-wavelength photometry, provide extinction-corrected Hα star formation rates (SFR), gas phase metallicities from [N ii]/Hα, and stellar masses. We measure an integrated Hα SFR of ~325 ${M}_{\odot }\;{\mathrm{yr}}^{-1}$ (26 members; R${}_{\mathrm{proj}}$ $\;\lt \;2$ Mpc) and show that the elevated star formation in the cluster core (R${}_{\mathrm{proj}}$ $\;\lt \;0.25$ Mpc) is driven by the concentration of star-forming members, but the average SFR per Hα-detected galaxy is half that of members at R${}_{\mathrm{proj}}$ ~ 1 Mpc. However, we do not detect any environmental imprint when comparing attenuation and gas phase metallicities: the cluster galaxies show similar trends with ${M}_{\star }$ as to the field, e.g., more massive galaxies have larger stellar attenuation. IRC 0218's gas phase metallicity–${M}_{\star }$ relation (MZR) is offset to lower metallicities relative to $z\sim 0$ and has a slope of 0.13 ± 0.10. Comparing the MZR in IRC 0218 to the COSMOS cluster at z = 2.1 shows no evolution (${\rm{\Delta }}t\sim 1$ Gyr): the MZR for both galaxy clusters are remarkably consistent with each other and virtually identical to several field surveys at $z\sim 2$.