Tracing the History of Recent Bulge Star Formation in Active Galactic Nuclei

TL;DR

This study investigates the connection between black hole growth and recent star formation in galaxy bulges of obscured AGNs, revealing a power-law relation that varies with look-back time and bulge age.

Contribution

It introduces a detailed analysis of the evolving relationship between AGN accretion rates and recent star formation, using a large SDSS sample and population synthesis.

Findings

Power-law relation between Eddington ratio and specific star formation rate for tau < tau_0.

The relation flattens for tau > tau_0, with tau_0 ~ 0.1 Gyr in young bulges and ~1 Gyr in old bulges.

Scatter dominated by observational uncertainties.

Abstract

We examine the relation between black hole accretion and bulge star formation as a function of look-back time (tau) in 20,541 obscured AGNs (with redshifts <z> ~ 0.1 and bolometric luminosities L_Bol ~ 10^43--10^45 erg s^-1) optically selected from the Sloan Digital Sky Survey (SDSS). To quantify the most recently formed stars with ages less than typical AGN lifetimes, we estimate the differentiated specific star formation rate (SSFR_tau) based on population synthesis analysis. Eddington ratio (lambda) is inferred using [O III]5007 luminosity and stellar velocity dispersion as proxies for L_Bol and black hole mass respectively. We find that when tau < tau_0, SDSS AGNs follow a power law: lambda \propto (SSFR_tau)^1.0-1.1; the relation flattens out when tau > tau_0. The threshold timescale tau_0 is ~ 0.1 (~ 1) Gyr in young (old) bulges. The scatter in the power laws is dominated by observational uncertainties. These results may provide useful constraints on models explaining the correlations between AGN activity and bulge star formation.