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Published September 21, 2015 | Submitted + Published
Journal Article Open

The formation history of massive cluster galaxies as revealed by CARLA


We use a sample of 37 of the densest clusters and protoclusters across 1.3 ≤ z ≤ 3.2 from the Clusters Around Radio-Loud AGN (CARLA) survey to study the formation of massive cluster galaxies. We use optical i′-band and infrared 3.6 and 4.5 μm images to statistically select sources within these protoclusters and measure their median observed colours; 〈i′ − [3.6]〉. We find the abundance of massive galaxies within the protoclusters increases with decreasing redshift, suggesting these objects may form an evolutionary sequence, with the lower redshift clusters in the sample having similar properties to the descendants of the high-redshift protoclusters. We find that the protocluster galaxies have an approximately unevolving observed-frame i′ − [3.6] colour across the examined redshift range. We compare the evolution of the 〈i′ − [3.6]〉 colour of massive cluster galaxies with simplistic galaxy formation models. Taking the full cluster population into account, we show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2 Gyr, and peaks at z ∼ 2–3. From the median i′ − [3.6] colours, we cannot determine the star formation histories of individual galaxies, but their star formation must have been rapidly terminated to produce the observed red colours. Finally, we show that massive galaxies at z > 2 must have assembled within 0.5 Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in z > 2 protoclusters could have formed via dry mergers.

Additional Information

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 June 23. Received 2015 May 28. In original form 2015 March 17. First published online July 24, 2015. We would like to thank Anthony Gonzalez for useful comments and suggestions. We also thank the CARLA team for producing the survey on which this paper is based. We thank the anonymous referee for their careful review and helpful comments, which improved the content of the paper. We are grateful to Fiona Riddick, Cecilia Fariña, Raine Karjalainen, James McCormac and Berto González for all their help and support with the observations at the WHT. EAC acknowledges support from the STFC. NAH is supported by an STFC Rutherford Fellowship. The work of DS was carried out at Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. SIM acknowledges the support of the STFC consolidated grant (ST/K001000/1). NS is the recipient of an ARC Future Fellowship. Based on observations made with the William Herschel Telescope under programme IDs W/2013b/10, W/2014a/6 and SW/2013b/34, and the Gemini Observatory under programme ID GS-2014A-Q-45. The William Herschel Telescope operates on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.

Attached Files

Published - MNRAS-2015-Cooke-2318-36.pdf

Submitted - 1507.00350v1.pdf


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