What triggers black-hole growth? Insights from star formation rates

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We present a new semi-analytic model for the common growth of black holes (BHs) and galaxies within a hierarchical Universe.

• The model is tuned to match the mass function of BHs at z=0 and the luminosity functions of active galactic nuclei (AGNs) at z<4.
• We use a new observational constraint, which relates the luminosity of AGNs to the star-formation rate (SFR) of their host galaxies.
• We show that this new constraint is important in various aspects: a) it indicates that BH accretion events are episodic; b) it favours a scenario in which BH accretion is triggered by merger events of all mass ratios; c) it constrains the duration of both merger-induced star-bursts and BH accretion events.