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HST Grism Confirmation of 16 Structures at 1.4<z<2.8 from the Clusters Around Radio-Loud AGN (CARLA) Survey

Noirot, Gaël; Stern, Daniel; Mei, Simona; Wylezalek, Dominika; Cooke, Elizabeth A.; De Breuck, Carlos; Galametz, Audrey; Hatch, Nina A.; Vernet, Joël; Brodwin, Mark; Eisenhardt, Peter; Gonzalez, Anthony H.; Jarvis, Matt; Rettura, Alessandro; Seymour, Nick; Stanford, S. A.

HST Grism Confirmation of 16 Structures at 1.4<z<2.8 from the Clusters Around Radio-Loud AGN (CARLA) Survey Thumbnail


Gaël Noirot

Daniel Stern

Simona Mei

Dominika Wylezalek

Elizabeth A. Cooke

Carlos De Breuck

Audrey Galametz

Joël Vernet

Mark Brodwin

Peter Eisenhardt

Anthony H. Gonzalez

Matt Jarvis

Alessandro Rettura

Nick Seymour

S. A. Stanford


We report spectroscopic results from our 40-orbit Hubble Space Telescope slitless grism spectroscopy program observing the 20 densest Clusters Around Radio-Loud AGN (CARLA) candidate galaxy clusters at 1.4 less than z less than 2.8. These candidate rich structures, among the richest and most distant known, were identified on the basis of [3.6]–[4.5] color from a 408 hr multi-cycle Spitzer program targeting 420 distant radio-loud AGN. We report the spectroscopic confirmation of 16 distant structures at 1.4less than z less than 2.8 associated with the targeted powerful high redshift radio-loud AGN. We also report the serendipitous discovery and spectroscopic confirmation of seven additional structures at 0.87 less than z less than 2.12 not associated with the targeted radio-loud AGN. We find that 1010–1011Me member galaxies of our confirmed CARLA structures form significantly fewer stars than their field counterparts at all redshifts within 1.4 less or equal z less or equal 2. We also observe higher star-forming activity in the structure cores up to z=2, finding similar trends as cluster surveys at slightly lower redshifts (1.0 less than z less than 1.5). By design, our efficient strategy of obtaining just two grism orbits per field only obtains spectroscopic confirmation of emission line galaxies. Deeper spectroscopy will be required to study the population of evolved, massive galaxies in these (forming) clusters. Lacking multi-band coverage of the fields, we adopt a very conservative approach of calling all confirmations “structures,” although we note that a number of features are consistent with some of them being bona fide galaxy clusters. Together this survey represents a unique and large homogenous sample of spectroscopically confirmed structures at high redshifts, potentially more than doubling the census of confirmed, massive clusters at z>1.4.


Noirot, G., Stern, D., Mei, S., Wylezalek, D., Cooke, E. A., De Breuck, C., …Stanford, S. A. (2018). HST Grism Confirmation of 16 Structures at 1.4

Journal Article Type Article
Acceptance Date Feb 11, 2018
Online Publication Date May 21, 2018
Publication Date May 21, 2018
Deposit Date Jan 8, 2019
Publicly Available Date Jan 8, 2019
Journal The Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 859
Issue 1
Article Number 38
Public URL
Publisher URL


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