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arXiv · 1301.3922

Concurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters

B. D. Lehmer·A. B. Lucy·D. M. Alexander·P. N. Best·J. E. Geach·C. M. Harrison·A. E. Hornschemeier·Y. Matsuda·J. R. Mullaney·Ian Smail·D. Sobral·A. M. Swinbank
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Abstract

We present results from a ~100 ks Chandra observation of the 2QZ Cluster 1004+00 structure at z = 2.23 (hereafter, 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four optically-selected QSOs at z = 2.23 within a 15x15 arcmin^2 region. Narrow-band imaging in the near-IR revealed that the structure contains an additional overdensity of 22 z = 2.23 Halpha-emitting galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs. Our Chandra observations reveal that 3 HAEs in addition to the 4 QSOs harbor powerfully accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of ~(8-60) x 10^43 ergs/s and X-ray spectral slopes consistent with unobscured AGN. Using a large comparison sample of 210 HAEs in Chandra-COSMOS (C-COSMOS), we find suggestive evidence that the AGN fraction increases with local HAE galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment (a factor of ~2 times over the field), and after excluding optically-selected QSOs, we find the AGN fraction is a factor of ~3.5^+3.8_-2.2 times higher than C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra data and Herschel SPIRE observations at 250 um, we respectively estimate mean SMBH accretion rates (Mdot) and star-formation rates (SFRs) for the 2QZ Clus and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked 2-10 keV luminosity is QSO-like (~6-10 x 10^43 ergs/s), and the implied Mdot/SFR \sim (1.6-3.2) x10^-3 is broadly consistent with the local MBH/M* relation and z ~ 2 X-ray selected AGN. The C-COSMOS HAEs are on average an order of magnitude less X-ray luminous and have Mdot/SFR \sim (0.2-0.4) x10^-3, comparable to z ~ 1-2 star-forming galaxies with similar mean X-ray luminosities. We estimate that a periodic QSO phase with duty cycle ~2-8% would be sufficient to bring the star-forming galaxies onto the local MBH/M* relation.

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B. D. Lehmer, A. B. Lucy, D. M. Alexander, P. N. Best, J. E. Geach, C. M. Harrison, A. E. Hornschemeier, Y. Matsuda, J. R. Mullaney, Ian Smail, D. Sobral, A. M. Swinbank. 2013-01-16. Concurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters. https://doi.org/10.1088/0004-637x/765/2/87

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