Kinematics of disk galaxies in (proto-)clusters atz= 1.5

Abstract

Aims.While many aspects of the impact of dense environments on late-type galaxies at redshifts below unity have been scrutinized in the past few decades, observational studies of the interplay between environment and disk galaxy evolution atz > 1 are still scarce. We observed star-forming galaxies atz ≈ 1.5 selected from the HyperSuprimeCam Subaru Strategic Program. The galaxies are part of two significant overdensities of [O II] emitters identified via narrowband imaging and photometric redshifts fromgrizyphotometry.Methods.We used theK-band Multi-Object Spectrograph (KMOS) to carry out Hαintegral field spectroscopy of 46 galaxies in total. Ionized gas maps, star formation rates, and velocity fields were derived from the Hαemission line. We quantified morphological and kinematical asymmetries in order to look for potential gravitational (e.g., galaxy-galaxy) or hydrodynamical (e.g., ram-pressure) interactions.Results.Hαemission was detected in 36 of our targets. Of these galaxies, 34 are members of two (proto-)clusters atz = 1.47, confirming our selection strategy to be highly efficient. By fitting model velocity fields to the observed ones, we determined the intrinsic maximum rotation velocityVmaxof 14 galaxies. Utilizing the luminosity–velocity (Tully–Fisher) relation, we find that these galaxies are more luminous than their local counterparts of similar mass by up to ∼4 mag in the rest-frameB-band. In contrast to field galaxies atz < 1, the offsets of thez ≈ 1.5 (proto-)cluster galaxies from the local Tully–Fisher relation are not correlated with their star formation rates but with the ratio betweenVmaxand gas velocity dispersionσg. This probably reflects that fewer disks have settled to purely rotational kinematics and highVmax/σgratios, as is observed in the field at similar redshifts. Tests with degraded low-redshift cluster galaxy data show that we cannot identify purely hydrodynamical interactions with the imaging currently at hand. Due to relatively low galaxy velocity dispersions (σv < 400 km s−1) of the (proto-)clusters, gravitational interactions are likely more efficient, resulting in higher kinematical asymmetries than in present-days clusters.