The starburst-AGN connection: the role of young stellar populations in fueling supermassive black holes

Tracing the star formation history in circumnuclear regions (CNRs) is a key step towards understanding the starburst-AGN connection. However, bright nuclei outshining the entire host galaxy prevent the analysis of the stellar populations of CNRs around type-I AGNs. Obscuration of the nuclei by the central torus provides an unique opportunity to study the stellar populations of AGN host galaxies. We assemble a sample of 10, 848 type-II AGNs with a redshift range of $0.03\le z\le 0.08$ from the Sloan Digital Sky Survey’s Data Release 4, and measure the mean specific star formation rates (SSFRs) over the past 100Myr in the central $\sim1-2$ kpc . We find a tight correlation between the Eddington ratio ($\lambda$) of the central black hole (BH) and the mean SSFR, strongly implying that supernova explosions (SNexp) play a role in the transportation of gas to galactic centers. We outline a model for this connection by accounting for the role of SNexp in the dynamics of CNRs. In our model, the viscosity of turbulence excited by SNexp is enhanced, and thus angular momentum can be efficiently transported, driving inflows towards galactic centers. Our model explains the observed relation $\lambda \propto \rm SSFR^{1.5-2.0}$, suggesting that AGN are triggered by SNexp in CNRs.

💡 Research Summary

The authors address a long‑standing obstacle in studying the starburst–AGN connection: the bright nucleus of type‑I AGN overwhelms the host galaxy’s stellar light, making it difficult to reconstruct the recent star formation history in the circumnuclear region (CNR). By focusing on type‑II AGN, whose central engines are obscured by the dusty torus, they can isolate the host galaxy’s spectrum and measure the specific star formation rate (SSFR) within the inner ∼1–2 kpc.

Using the Sloan Digital Sky Survey Data Release 4, they compile a sample of 10 848 type‑II AGN with redshifts 0.03 ≤ z ≤ 0.08. After removing the AGN continuum with spectral decomposition tools, they derive the recent (last 100 Myr) mean SSFR from the Dₙ4000 break and Hδ_A absorption index, which are sensitive to young stellar populations. Black‑hole masses are estimated via the M–σ relation and the width of the