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Excess AGN activity in the z = 2.30 Protocluster in HS 1700+64

Digby-North, J. A. and Nandra, K. and Laird, E. S. and Steidel, C. C. and Georgakakis, A. and Bogosavljević, M. and Erb, D. K. and Shapley, A. E. and Reddy, N. A. and Aird, J. (2010) Excess AGN activity in the z = 2.30 Protocluster in HS 1700+64. Monthly Notices of the Royal Astronomical Society, 407 (2). pp. 846-853. ISSN 0035-8711.

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We present the results of spectroscopic, narrow-band and X-ray observations of a z= 2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of BX/MD galaxies, which are selected to be at z ~ 2.2–2.7 by their rest-frame ultraviolet colours, we find that there are five protocluster AGN which have been identified by characteristic emission-lines in their optical/near-IR spectra; this represents an enhancement over the field significant at >98.5 per cent confidence. Using a ~200-ks Chandra/ACIS-I observation of this field we detect a total of 161 X-ray point sources to a Poissonian false-probability limit of 4 × 10^(−6) and identify eight of these with BX/MD galaxies. Two of these are spectroscopically confirmed protocluster members and are also classified as emission-line AGN. When compared to a similarly selected field sample, the analysis indicates this is also evidence for an enhancement of X-ray selected BX/MD AGN over the field, significant at >99 per cent confidence. Deep Lyα narrow-band imaging reveals that a total of 4/123 Lyα emitters (LAEs) are found to be associated with X-ray sources, with two of these confirmed protocluster members and one highly likely member. We do not find a significant enhancement of AGN activity in this LAE sample over that of the field (result is significant at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD and LAE samples are found to be 6.9^(+9.2)_(−4.4) and 2.9^(+2.9)_(−1.6) per cent, respectively, for protocluster AGN with L_(2-10 keV)≥ 4.6 × 10^(43) erg s^(−1) at z= 2.30. These findings are similar to results from the z= 3.09 protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both suggest AGN activity is favoured in dense environments at z > 2.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
Nandra, K.0000-0002-7150-9192
Steidel, C. C.0000-0002-4834-7260
Erb, D. K.0000-0001-9714-2758
Shapley, A. E.0000-0003-3509-4855
Reddy, N. A.0000-0001-9687-4973
Aird, J.0000-0003-1908-8463
Additional Information:© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 May 6. Received 2010 May 6; in original form 2009 September 21. Article first published online: 18 Jun 2010. We thank the anonymous referee for their comments which significantly improved this paper. JADN and ESL acknowledge generous financial support from the STFC. KN acknowledges the support of the Royal Society. This work is based on observations taken with the Chandra X-Ray Observatory, which is operated for NASA by the Smithsonian Astrophysical Observatory.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:galaxies: active; galaxies: clusters: general; galaxies: high-redshift; surveys; X-rays: general
Issue or Number:2
Record Number:CaltechAUTHORS:20101004-101154180
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Official Citation:Digby-North, J. A., Nandra, K., Laird, E. S., Steidel, C. C., Georgakakis, A., Bogosavljević, M., Erb, D. K., Shapley, A. E., Reddy, N. A. and Aird, J. (2010), Excess AGN activity in the z= 2.30 Protocluster in HS 1700+64. Monthly Notices of the Royal Astronomical Society, 407: 846–853. doi: 10.1111/j.1365-2966.2010.16977.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20273
Deposited By: Tony Diaz
Deposited On:16 Nov 2010 23:29
Last Modified:09 Mar 2020 13:19

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