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ALMA observations of a z ≈ 3.1 protocluster: Star formation from active galactic nuclei and Lyman-alpha blobs in an overdense environment

Lookup NU author(s): Dr Christopher HarrisonORCiD



This is the final published version of an article that has been published in its final definitive form by Oxford University Press, 2016.

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© 2016 The Authors. We exploit Atacama Large Interferometer Array (ALMA) 870 μm observations to measure the star formation rates (SFRs) of eight X-ray detected active galactic nuclei (AGNs) in a z ≈ 3.1 protocluster, four of which reside in extended Lyα haloes (often termed Lymanalpha blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ≈220-410 M⊙ yr-1; the non-detection of the other five AGNs places SFR upper limits of ≲210 M⊙ yr-1. The mean SFR of the protocluster AGNs (≈110-210 M⊙ yr-1) is consistent (within a factor of ≈0.7-2.3) with that found for co-eval AGNs in the field, implying that the galaxy growth is not significantly accelerated in these systems. However, when also considering ALMA data from the literature, we find evidence for elevated mean SFRs (up-to a factor of ≈5.9 over the field) for AGNs at the protocluster core, indicating that galaxy growth is significantly accelerated in the central regions of the protocluster. We also show that all of the four protocluster LABs are associated with an ALMA counterpart within the extent of their Lyα emission. The SFRs of the ALMA sources within the LABs (≈150-410 M⊙ yr-1) are consistent with those expected for co-eval massive star-forming galaxies in the field. Furthermore, the two giant LABs (with physical extents of ≳100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Lyα emission. We use these results to discuss star formation as the power source of LABs.

Publication metadata

Author(s): Alexander DM, Simpson JM, Harrison CM, Mullaney JR, Smail I, Geach JE, Hickox RC, Hine NK, Karim A, Kubo M, Lehmer BD, Matsuda Y, Rosario DJ, Stanley F, Swinbank AM, Umehata H, Yamada T

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2016

Volume: 461

Issue: 3

Pages: 2944-2952

Print publication date: 21/09/2016

Online publication date: 26/06/2016

Acceptance date: 21/06/2016

Date deposited: 04/02/2020

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press


DOI: 10.1093/mnras/stw1509


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