We present deep Gemini GMOS-S optical broad-band images for a complete sample of 20 SDSS selected type II quasars taken from Zakamska et al .
( 81 ) , with redshifts in the range 0.3 < z < 0.41 and [ OIII ] \lambda 5007 emission line luminosities L _ { [ OIII ] } > 10 ^ { 8.5 } L _ { \odot } .
The images were taken with the aim of investigating the interaction status of the quasar host galaxies , in order to determine the significance of galaxy interactions in triggering nuclear activity .
We find that 15 of our sample of 20 ( 75 \pm 20 \% ) show evidence for interaction in the form of tails , shells , fans , irregular features , amorphous halos and double nuclei .
The median surface brightness of the features is \tilde { \mu } _ { r } ^ { corr } = 23.4 ~ { } mag~ { } arcsec ^ { -2 } and the range is \Delta \mu _ { r } ^ { corr } \simeq [ 20.9 , 24.7 ] ~ { } mag~ { } arcsec ^ { -2 } .

We find a similar rate of interaction signatures in the type II quasars as in a comparison sample of quiescent early-type galaxies at similar redshift ( 67 \pm 14 \% ) taken from Ramos Almeida et al .
( 58 ) .
However the surface brightness of the detected features is up to 2 magnitudes brighter for the type II quasars than for the quiescent early-types , which have surface brightnesses in the range \Delta \mu _ { r } ^ { corr } \simeq [ 22.1 , 26.1 ] ~ { } mag~ { } arcsec ^ { -2 } and a median surface brightness \tilde { \mu } _ { r } ^ { corr } = 24.3 ~ { } mag~ { } arcsec ^ { -2 } .
Despite the relatively small sample size , this may indicate that the mergers witnessed in the comparison sample galaxies could have different progenitors , or we may be viewing the interactions at different stages .
We also compare our results with those of Ramos Almeida et al .
( 57 ) who made a similar analysis using a complete sample of radio-loud AGN .
They find a higher rate of interaction signatures in the radio loud AGN ( 95 ^ { ~ { } +5 } _ { -21 } \% ) than the type II quasars , but a very similar range of surface brightnesses for the morphological features \Delta \mu _ { r } ^ { corr } \simeq [ 20.9 , 24.8 ] ~ { } mag~ { } arcsec ^ { -2 } , possibly indicating a similarity in the types of triggering interactions .

The wide range of features detected in the type II quasar sample suggests that AGN activity can be triggered before , during or after the coalescence of the black holes , with 6 of the 20 objects ( 30 \pm 12 \% ) having double nuclei .
Overall , the results presented here are consistent with the idea that galaxy interaction plays an important role in the triggering of quasar activity .
We also use time scale arguments to show that it is unlikely that most radio-quiet quasars cycle through a radio-loud phase as part of a single quasar triggering event .