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HST grism confirmation of two z ~ 2 structures from the clusters around radio-loud AGN (CARLA) survey




Carlos De Breuck

Dominika Wylezalek

Audrey Galametz

Daniel Stern

Simona Mei

Mark Brodwin

Elizabeth A. Cooke

Anthony H. Gonzalez

Nina A. Hatch

Alessandro Rettura

Spencer A, Stanford


Using Hubble Space Telescope slitless grism data, we report the spectroscopic confirmation of two distant structures at z ~ 2 associated with powerful high-redshift radio-loud active galactic nuclei (AGNs). These rich structures, likely (forming) clusters, are among the most distant structures currently known, and were identified on the basis of Spitzer/IRAC [3.6]–[4.5] color. We spectroscopically confirm nine members in the field of MRC 2036−254, comprising eight star-forming galaxies and the targeted radio galaxy. The median redshift is z=2.000. We spectroscopically confirm 10 members in the field of B3 0756+406, comprising 8 star-forming galaxies and 2 AGNs, including the targeted radio-loud quasar. The median redshift is z=1.986. All confirmed members are within 500 kpc (1 arcmin) of the targeted AGNs. We derive median (mean) star-formation rates of ~35 Mʘ yr‾¹ (~50 M yr‾¹) for the confirmed star-forming members of both structures based on their [O III]ʎ5007 luminosities, and estimate average galaxy stellar masses ≲1 x 10¹¹ Mʘ based on mid-infrared fluxes and spectral energy distribution modeling. Most of our confirmed members are located above the star-forming main sequence toward starburst galaxies, consistent with clusters at these early epochs being the sites of significant levels of star formation. The structure around MRC 2036−254 shows an overdensity of IRAC-selected candidate galaxy cluster members consistent with being quiescent galaxies, while the structure around B3 0756+406 shows field values, albeit with many lower limits to colors that could allow an overdensity of faint red quiescent galaxies. The structure around MRC 2036−254 shows a red sequence of passive galaxy candidates.


Noirot, G., Vernet, J., De Breuck, C., Wylezalek, D., Galametz, A., Stern, D., …Stanford, S. A. (2016). HST grism confirmation of two z ~ 2 structures from the clusters around radio-loud AGN (CARLA) survey. Astrophysical Journal, 830(2),

Journal Article Type Article
Acceptance Date Jul 29, 2016
Publication Date Oct 14, 2016
Deposit Date Oct 28, 2016
Publicly Available Date Oct 28, 2016
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 830
Issue 2
Keywords Galaxies: Clusters: Individual (CARLA J2039-2514, CARLA J0800+4029) – Galaxies: High-redshift – Galaxies: Individual (MRC 2036-254, B3 0756+406)
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Noirot_2016_ApJ_830_90.pdf (6 Mb)

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