Fundamental differences in the radio properties of red and blue quasars:
  kiloparsec-scale structures revealed by e-MERLIN
  Red quasi-stellar objects (QSOs) are a subset of the quasar population with
colours consistent with reddening due to intervening dust. Recent work has
demonstrated that red QSOs show special radio properties that fundamentally
distinguish them from normal blue QSOs, specifically a higher incidence of
low-power radio emission (1.4 GHz luminosities L$_{\rm 1.4} \approx 10^{25}$ -
$10^{27}$ W Hz$^{-1}$) that is physically compact when imaged by
arcsecond-resolution radio surveys such as FIRST. In this work, we present
e-MERLIN imaging of a set of intermediate-redshift ($1.0<z<1.55$), luminous
(bolometric luminosities L$_{bol} \approx 10^{46}$ - $10^{47}$ erg s$^{-1}$)
red and normal QSOs carefully selected to have radio properties that span the
range over which red QSOs show the most divergence from the general population.
With an angular resolution $\times25$ better than FIRST, we resolve structures
within the host galaxies of these QSOs ($> 2$ kpc). We report a statistically
significant difference in the incidence of extended kpc-scale emission in red
QSOs. From an analysis of the radio size distributions of the sample, we find
that the excess radio emission in red QSOs can be attributed to structures that
are confined to galaxy scales ($< 10$ kpc), while we confirm previous results
that red and normal QSOs have similar incidences of radio jets and lobes on
circumgalactic or larger scales ($> 10$ kpc). Our results indicate that the
primary mechanism that generates the enhanced radio emission in red QSOs is not
directly connected with the nuclear engine or accretion disc, but is likely to
arise from extended components such as AGN-driven jets or winds.
