Spatially Resolved Spectroscopy of Starburst and Post-Starburst Galaxies in The Rich z~0.55 Cluster CL0016+16

TL;DR

This study uses spatially resolved spectroscopy to analyze starburst and post-starburst galaxies in a z~0.55 cluster, revealing insights into their star formation mechanisms and morphological characteristics.

Contribution

It provides the first spatially resolved spectral analysis of these galaxy types in a rich cluster at this redshift, highlighting the role of the intra-cluster medium and morphological features.

Findings

Post-starburst galaxies show no significant radial Hdelta gradients.

Dusty-starburst galaxies exhibit central OII3727 emission concentration.

Post-starburst galaxies lack tidal features, suggesting intra-cluster medium effects rather than mergers.

Abstract

We have used the Low Resolution Imaging Spectrograph (LRIS) on the W.M. Keck I telescope to obtain spatially resolved spectroscopy of a small sample of six post-starburst and three dusty-starburst galaxies in the rich cluster CL0016+16 at z=0.55. We use this to measure radial profiles of the Hdelta and OII3727 lines which are diagnostic probes of the mechanisms that give rise to the abrupt changes in star-formation rates in these galaxies. In the post-starburst sample we are unable to detect any radial gradients in the Hdelta line equivalent width - although one galaxy exhibits a gradient from one side of the galaxy to the other. The absence of Hdelta gradients in these galaxies is consistent with their production via interaction with the intra-cluster medium, however, our limited spatial sampling prevents us from drawing robust conclusions. All members of the sample have early type morphologies, typical of post-starburst galaxies in general, but lack the high incidence of tidal tails and disturbances seen in local field samples. This argues against a merger origin and adds weight to a scenario where truncation by the intra-cluster medium is at work. The post-starburst spectral signature is consistent over the radial extent probed with no evidence of OII3727 emission and strong Hdelta absorption at all radii i.e. the post-starburst classification is not an aperture effect. In contrast the dusty-starburst sample shows a tendency for a central concentration of OII3727 emission. This is most straightforwardly interpreted as the consequence of a central starburst. However, other possibilities exist such as a non-uniform dust distribution (which is expected in such galaxies) and/or a non-uniform starburst age distribution. The sample exhibit late type and irregular morphologies.