Effect of bars in AGN host galaxies and black hole activity

Abstract

Aims. With the aim of assessing the effects of bars on active galactic nuclei (AGN), we present an analysis of host characteristics and nuclear activity of active galaxies with and without bars. Methods. We selected AGN host galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7), using the available emission-line fluxes. By visual inspection of SDSS images we classified the face-on spiral hosts of AGNs brighter than g-mag < 16.5 into barred or unbarred. With the purpose of providing an appropriate quantification of the effects of bars, we also constructed a suitable control sample of unbarred active galaxies with similar redshift, magnitude, morphology, bulge sizes, and local environment distributions. Results. We find that the bar fraction, with respect to the full sample of spiral face-on AGN host galaxies, is 28.5%, in good agreement with previous works. barred AGN host galaxies show an excess of young stellar populations (as derived with the Dn(4000) spectral index), dominated by red u − r and g − r colors, with respect to the control sample, suggesting that bars produce an important effect on galaxy properties of AGN hosts. Regarding the nuclear activity distribution, we find that barred active galaxies show a shift toward higher Lum [OIII] values with respect to AGN without bars. In addition, we also find that this trend is more significant in less massive, younger stellar population and bluer AGN host galaxies. We found that the fraction of powerful AGN increases toward more massive hosts with bluer colors and younger stellar populations residing in denser environments. However, barred host AGN systematically show a higher fraction of powerful active nuclei galaxies with respect to the control sample. We also explored the accretion rate onto the central black holes, finding that barred AGN host show an excess of objects with high accretion rate values with respect to unbarred active galaxies