The insignificance of Seyfert 2 activity in driving cold-gas galactic winds

Abstract

We study the interstellar Na I λλ5890, 5895 (Na D) absorption-line doublet in a large sample of ∼9900 nearby Seyfert 2 galaxies, in order to quantify the significance of optical, unobscured AGN activity in driving kpc-scale outflows that can quench star formation. Comparison to a carefully matched sample of ∼44 000 control objects indicates that the Seyfert and control population have similar Na D detection rates (∼ 5-6 per cent). Only 53 Seyferts (or 0.5 per cent of the population) are found to potentially display galactic-scale winds, compared to 0.8 per cent of the control galaxies. While nearly a third of the Na D outflows observed in our Seyfert 2 galaxies occur around the brightest AGN, both radio and infrared data indicate that star formation could play the dominant role in driving cold-gas outflows in an even higher fraction of the Na D-outflowing Seyfert 2s. Our results indicate that galactic-scale outflows at low redshift are no more frequent in Seyferts than they are in their control-sample counterparts, that optical AGN are not direct significant contributors to the quenching of star formation in the nearby Universe, and that star-formation may actually be the principal driver of outflows even in systems that do host an unobscured AGN.