Galaxy pairs in the Sloan Digital Sky Survey - XII: The fuelling
  mechanism of low excitation radio-loud AGN
  We investigate whether the fuelling of low excitation radio galaxies (LERGs)
is linked to major galaxy interactions. Our study utilizes a sample of 10,800
spectroscopic galaxy pairs and 97 post-mergers selected from the Sloan Digital
Sky Survey with matches to multi-wavelength datasets. The LERG fraction amongst
interacting galaxies is a factor of 3.5 higher than that of a control sample
matched in local galaxy density, redshift and stellar mass. However, the LERG
excess in pairs does not depend on projected separation and remains elevated
out to at least 500 kpc, suggesting that major mergers are not their main
fuelling channel. In order to identify the primary fuelling mechanism of LERGs,
we compile samples of control galaxies that are matched in various host galaxy
and environmental properties. The LERG excess is reduced, but not completely
removed, when halo mass or D4000 are included in the matching parameters.
However, when BOTH M_halo and D4000 are matched, there is no LERG excess and
the 1.4 GHz luminosities (which trace jet mechanical power) are consistent
between the pairs and control. In contrast, the excess of optical and mid-IR
selected AGN in galaxy pairs is unchanged when the additional matching
parameters are implemented. Our results suggest that whilst major interactions
may trigger optically and mid-IR selected AGN, the gas which fuels the LERGs
has two secular origins: one associated with the large scale environment, such
as accretion from the surrounding medium or minor mergers, plus an internal
stellar mechanism, such as winds from evolved stars.
