The host galaxies of AGN with powerful relativistic jets

We present deep Near-infrared (NIR) images of a sample of 19 intermediate-redshift (0.3<z<1.0)  radio-loud active galactic nuclei  (AGN) with powerful  relativistic jets  (L1.4GHz >10^27 WHz^-1),  previously classified as flat-spectrum radio quasars. We also compile host galaxy and nuclear magnitudes  for  blazars from literature.  The combined sample (this work and compilation) contains 100 radio-loud AGN with host galaxy detections and a broad range of radio luminosities L1.4GHz = 10^23.7 - 10^28.3WHz^-1, allowing us to divide our sample into high-excitation (quasar-mode; HERGs) and low-excitation (radio-mode; LERGs) radio galaxies. The host galaxies of our sample are bright and seem to follow the Kormendy relation. Nuclear emission (dominated by non-thermal mechanisms) and host-galaxy magnitudes show a slightly negative weak trend for LERGs. On the other hand, the m_bulge -m_nuc relation is statistically significant for HERGs. Although it may be affected by selection effects, this correlation suggests a close coupling between the relativistic jets and their host galaxy. Our findings are consistent with the excitation state (LERG/HERG) scenario. In this view, LERGs emit the bulk of their energy in the form of radio jets, producing a strong feedback mechanism, and HERGs are affected by galaxy mergers and interactions, which provide a common supply of cold gas to feed both nuclear activity and star formation episodes.