The host galaxies of active galactic nuclei

Abstract

We examine the properties of the host galaxies of 22 623 narrow‐line active galactic nuclei (AGN) with 0.02 < z < 0.3 selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O iii]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L[O iii]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early‐type galaxies in our sample. The host galaxies of low‐luminosity AGN have stellar populations similar to normal early types. The hosts of high‐luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high‐luminosity AGN have strong Hδ absorption‐line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad‐line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O iii] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O iii] luminosities.

Starburst–AGN mixing – II. Optically selected active galaxies

“…A large number of AGN host galaxies lie in the 'Green Valley' of the galaxy colour-magnitude diagram (e.g. Kauffmann et al 2003;Sánchez et al 2004;Georgakakis et al 2008). The green colors of these galaxies suggest that star formation is on the way to being quenched as part of a transition phase from the blue cloud to the red sequence (Schawinski et al 2010).…”

The Co-Evolution of Galaxies and Black Holes: Current Status and Future Prospects

“…There are also systematic trends in host properties with AGN luminosity (Cid Fernandes et al 2001;Kauffmann et al 2003c;Kauffmann et al 2007;Wild et al 2007). The higher the luminosity of the AGN, the younger is the age of the stellar population in the centralmost few kpc, the higher is the likelihood that the galaxy has experienced a burst of star formation within the last gigayear, and the greater is the amount of dust extinction towards the bulge (a proxy for the presence of cold gas).…”

“…In the Type 2 Seyferts, the observed ultraviolet through near-infrared continuum is dominated by the host galaxy (e.g., Kauffmann et al 2003c). The presence of the obscured AGN can be recognized by the strong mid-infrared emission from the dusty torus, by the high-ionization narrow UV, optical, and IR emission-lines produced as the ionizing radiation from the accretion disk escapes along the polar axis of the torus and photoionizes gas in the surrounding kpcscale narrow-line region (NLR), and by hard X-rays that have passed directly through the torus (if the torus is Compton-thin).…”

“…These AGN were recognized by the emission of the NLR in the SDSS spectra (Kauffmann et al 2003c;Hao et al 2005). The AGN luminosity can be estimated from the strong [O iii] λ5007 emission line and an empirically derived bolometric correction , while the black hole mass can be determined from the bulge velocity dispersion σ and the M BH -σ relation (Tremaine et al 2002).…”

The ionization of galaxies by their planetary nebulae

“…Then, with the advent of the Sloan Digital Sky Survey (SDSS, York et al 2000), which produced spectra of nearly one million of galaxies, it was found that galaxies with integrated LINER-like spectra compose a large part of the entire population of galaxies in the nearby Universe (Kauffmann et al 2003). The source of ionization of 240 G. Stasińska…”