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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Sun, M., Trump, J.R., Brandt, W.N., Luo, B., Alexander, D.M., Jahnke, K., Rosario, D.J., Wang, S.X. & Xue, Y.Q. (2015). Evolution in the Black Hole-Galaxy Scaling Relations and the Duty Cycle of Nuclear Activity in Star-forming Galaxies. The Astrophysical Journal 802(1): 14.

Author(s) from Durham


We measure the location and evolutionary vectors of 69 Herschel-detected broad-line active galactic nuclei
(BLAGNs) in the M M - * BH plane. BLAGNs are selected from the COSMOS and CDF-S fields, and span the
redshift range 0.2 2. ⩽ z < 1. Black hole masses are calculated using archival spectroscopy and single-epoch virial
mass estimators, and galaxy total stellar masses are calculated by fitting the spectral energy distribution
(subtracting the BLAGN component). The mass-growth rates of both the black hole and galaxy are calculated
using Chandra/XMM-Newton X-ray and Herschel far-infrared data, reliable measures of the BLAGN accretion and
galaxy star formation rates, respectively. We use Monte Carlo simulations to account for biases in our sample, due
to both selection limits and the steep slope of the massive end of the galaxy stellar-mass distribution. We find our
sample is consistent with no evolution in the M M - * BH relation from z ∼ 2 to z ∼ 0. BLAGNs and their host
galaxies which lie off the black hole mass–galaxy total stellar mass relation tend to have evolutionary vectors anticorrelated
with their mass ratios: that is, galaxies with over-massive (under-massive) black holes tend to have a
low (high) ratio of the specific accretion rate to the specific star formation rate. We also use the measured growth
rates to estimate the preferred AGN duty cycle for our galaxies to evolve most consistently onto the local
M M BH Bul - relation. Under reasonable assumptions of exponentially declining star formation histories, the data
suggest a non-evolving (no more than a factor of a few) BLAGN duty cycle among star-forming galaxies of ∼10%
(1σ range of 1–42% at z < 1 and 2–34% at z > 1).