Prevalence of Tidal Interactions among Local Seyfert Galaxies: The Control Experiment

TL;DR

This study compares HI observations of inactive and Seyfert galaxies, revealing a significantly higher prevalence of tidal disturbances in Seyferts, suggesting tidal interactions may trigger Seyfert activity.

Contribution

It provides the first control sample comparison showing the difference in HI disturbances between inactive and Seyfert galaxies, supporting tidal interactions as a trigger for Seyfert activity.

Findings

~15% of control galaxies show HI disturbances

~94% of Seyfert galaxies show HI disturbances

Tidal interactions are likely linked to Seyfert activity

Abstract

We test whether there is a relation between the observed tidal interactions and Seyfert activity by imaging in HI twenty inactive galaxies at the same spatial resolution and detection threshold as the Seyfert sample. This control sample of inactive galaxies were closely matched in Hubble type, range in size and inclination, and have roughly comparable galaxy optical luminosity to the Seyfert galaxies. We find that only ~15% of the galaxies in our control sample are disturbed in HI, whereas the remaining ~85% show no disturbances whatsoever in HI. Even at a spatial resolution of ~10 kpc, none of the latter galaxies show appreciable HI disturbances reminiscent of tidal features. In a companion paper (Kuo et al. 2008), we report results from the first systematic imaging survey of Seyfert galaxies in atomic hydrogen (HI) gas. We find that only ~28% of the eighteen Seyfert galaxies in that sample are visibly disturbed in optical starlight. By contrast, ~94% of the same Seyfert galaxies are disturbed spatially and usually also kinematically in HI gas on galactic scales of >~20 kpc. In at least ~67% and up to perhaps ~94% of cases, the observed disturbances can be traced to tidal interactions with neighboring galaxies detected also in HI. The dramatic contrast between the observed prevalence of HI disturbances in the Seyfert and control samples implicates tidal interactions in initiating events that lead to luminous Seyfert activity in a large fraction of local disk galaxies.