A Census of Broad-Line Active Galactic Nuclei in Nearby Galaxies: Coeval Star Formation and Rapid Black Hole Growth

TL;DR

This study maps the distribution of broad-line AGNs in nearby galaxies, revealing their prevalence in star-forming and transitional galaxies, and suggesting simultaneous fueling of black hole growth and star formation.

Contribution

It provides the first statistical analysis of broad-line AGN frequency across galaxy colors and masses, highlighting their occurrence during specific galaxy evolutionary phases.

Findings

Broad-line AGNs are common in blue and green galaxies, rare in red galaxies.

More luminous AGNs are found in bluer host galaxies at fixed mass.

Evidence suggests simultaneous star formation and black hole fueling processes.

Abstract

We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey (SDSS) are used to dis- entangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid supermassive black hole accretion. If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the broad-line AGN phase.