Star Formation In The Cluster Merger DLSCL J0916.2+2953

Abstract

We investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z=0.53 that has progressed $1.1_{-0.4}^{+1.3}$ Gyr since first pass-through. We attempt to reveal the effects a collision may have had on the evolution of the cluster galaxies by tracing their star formation history. We probe current and recent activity to identify a possible star formation event at the time of the merger using EW(Hd), EW([OII]), and D${}_n$4000 measured from the composite spectra of 64 cluster and 153 coeval field galaxies. We supplement $Keck$ DEIMOS spectra with DLS and $HST$ imaging to determine the color, stellar mass, and morphology of each galaxy and conduct a comprehensive study of the populations in this complex structure. Spectral results indicate the average cluster and cluster red sequence galaxies experienced no enhanced star formation relative to the surrounding field during the merger, ruling out a predominantly merger-quenched population. We find that the average blue galaxy in the North cluster is currently active and in the South cluster is currently post-starburst having undergone a recent star formation event. While the North activity could be latent or long-term merger effects, a young blue stellar population and irregular geometry suggest the cluster was still forming prior the collision. While the South activity coincides with the time of the merger, the blue early-type population could be a result of secular cluster processes. The evidence suggests that the dearth or surfeit of activity is indiscernible from normal cluster galaxy evolution.

9 figures, 4 tables, approx 22 pages

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Cited by in corpus (4)

• VIS3COS: III. environmental effects on the star formation histories of galaxies at z~0.8 seen in [OII], H$\delta$, and Dn4000
• The galaxy mass-size relation in CARLA clusters and proto-clusters at 1.4 < z < 2.8: larger cluster galaxy sizes
• Suppressed Star Formation by a Merging Cluster System
• Post-processing of galaxies due to major cluster mergers I. hints from galaxy colours and morphologies