Skip to main content

Research Repository

Advanced Search

Searching for obscured AGN in z ∼ 2 submillimetre galaxies

Chen, H.; Garrett, M.A.; Chi, S.; Thomson, A.P.; Barthel, P.D.; Alexander, D.M.; Muxlow, T.W.B.; Beswick, R.J.; Radcliffe, J.F.; Wrigley, N.H.; Guidetti, D.; Bondi, M.; Prandoni, I.; Smail, I.; McHardy, I.; Argo, M.K.

Searching for obscured AGN in z ∼ 2 submillimetre galaxies Thumbnail


H. Chen

M.A. Garrett

S. Chi

A.P. Thomson

P.D. Barthel

T.W.B. Muxlow

R.J. Beswick

J.F. Radcliffe

N.H. Wrigley

D. Guidetti

M. Bondi

I. Prandoni

I. McHardy

M.K. Argo


Aims. Submillimetre-selected galaxies (SMGs) at high redshift (z ∼ 2) are potential host galaxies of active galactic nuclei (AGN). If the local Universe is a good guide, ∼50% of the obscured AGN amongst the SMG population could be missed even in the deepest X-ray surveys. Radio observations are insensitive to obscuration; therefore, very long baseline interferometry (VLBI) can be used as a tool to identify AGN in obscured systems. A well-established upper limit to the brightness temperature of 105 K exists in star-forming systems, thus VLBI observations can distinguish AGN from star-forming systems via brightness temperature measurements. Methods. We present 1.6 GHz European VLBI Network (EVN) observations of four SMGs (with measured redshifts) to search for evidence of compact radio components associated with AGN cores. For two of the sources, e-MERLIN images are also presented. Results. Out of the four SMGs observed, we detect one source, J123555.14, that has an integrated EVN flux density of 201 ± 15.2 μJy, corresponding to a brightness temperature of 5.2 ± 0.7 × 105 K. We therefore identify that the radio emission from J123555.14 is associated with an AGN. We do not detect compact radio emission from a possible AGN in the remaining sources (J123600.10, J131225.73, and J163650.43). In the case of J131225.73, this is particularly surprising, and the data suggest that this may be an extended, jet-dominated AGN that is resolved by VLBI. Since the morphology of the faint radio source population is still largely unknown at these scales, it is possible that with a ∼10 mas resolution, VLBI misses (or resolves) many radio AGN extended on kiloparsec scales.


Chen, H., Garrett, M., Chi, S., Thomson, A., Barthel, P., Alexander, D., …Argo, M. (2020). Searching for obscured AGN in z ∼ 2 submillimetre galaxies. Astronomy & Astrophysics, 638, Article A113.

Journal Article Type Article
Acceptance Date Apr 10, 2020
Online Publication Date Jun 23, 2020
Publication Date 2020-06
Deposit Date Jul 22, 2020
Publicly Available Date Jul 22, 2020
Journal Astronomy and astrophysics.
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 638
Article Number A113
Public URL


Published Journal Article (995 Kb)

Copyright Statement
Chen, H., Garrett, M. A., Chi, S., Thomson, A. P., Barthel, P. D., Alexander, D. M., Muxlow, T. W. B., Beswick, R. J., Radcliffe, J. F., Wrigley, N. H., Guidetti, D., Bondi, M., Prandoni, I., Smail, I., McHardy, I. & Argo, M. K. (2020). Searching for obscured AGN in z ∼ 2 submillimetre galaxies. Astronomy & Astrophysics 638: A113, reproduced with permission, © ESO.

You might also like

Downloadable Citations