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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.

Alexander, D.M. and Simpson, J.M. and Harrison, C.M. and Mullaney, J.R. and Smail, I. and Geach, J.E. and Hickox, R.C. and Hine, N.K. and Karim, A. and Kubo, M. and Lehmer, B.D. and Matsuda, Y. and Rosario, D.J. and Stanley, F. and Swinbank, A.M. and Umehata, H. and Yamada, T. (2016) 'ALMA observations of a z ≈ 3.1 protocluster : star formation from active galactic nuclei and Lyman-alpha blobs in an overdense environment.', Monthly notices of the Royal Astronomical Society., 461 (3). pp. 2944-2952.


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 Lyman-alpha 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.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:21 June 2016
Date deposited:10 November 2016
Date of first online publication:26 June 2016
Date first made open access:10 November 2016

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