Kiloparsec-scale radio emission in Seyfert and LINER galaxies
  Seyfert and LINER galaxies are known to exhibit compact radio emission on
$\sim$ 10 to 100 parsec scales, but larger Kiloparsec-Scale Radio structures
(KSRs) often remain undetected in sub-arcsec high resolution observations. We
investigate the prevalence and nature of KSRs in Seyfert and LINER galaxies
using the 1.4 GHz VLA FIRST and NVSS observations. Our sample consists of 2651
sources detected in FIRST and of these 1737 sources also have NVSS
counterparts. Considering the ratio of total to peak flux density ($\theta$ $=$
${\rm (S_{\rm int}/S_{\rm peak})^{1/2}}$) as a parameter to infer the presence
of extended radio emission we show that $\geq$ 30$\%$ of FIRST detected sources
possess extended radio structures on scales larger than 1.0 kpc. The use of
low-resolution NVSS observations help us to recover faint extended KSRs that
are resolved out in FIRST observations and results in $\geq$ 42.5$\%$ KSR
sources in FIRST-NVSS subsample. This fraction is only a lower limit owing to
the combination of projection, resolution and sensitivity effects. Our study
demonstrates that KSRs may be more common than previously thought and are found
across all redshifts, luminosities and radio-loudness. The extranuclear radio
luminosity of KSR sources is found to be positively correlated with the core
radio luminosity as well as the [O~III] $\lambda$5007{\AA} line luminosity and
this can be interpreted as KSRs being powered by AGN rather than
star-formation. The distributions of the FIR-to-radio ratios and mid-IR colors
of KSR sources are also consistent with their AGN origin. However, contribution
from star-formation cannot be ruled out particularly in sources with low radio
luminosities.
