Radio monitoring of NGC 7469: Late time radio evolution of SN 2000ft and
  the circumnuclear starburst in NGC 7469
  We present the results of an eight-year long monitoring of the radio emission
from the Luminous Infrared Galaxy (LIRG) NGC 7469, using 8.4 GHz Very Large
Array (VLA) observations at 0.3'' resolution. Our monitoring shows that the
late time evolution of the radio supernova SN 2000ft follows a decline very
similar to that displayed at earlier times of its optically thin phase. The
late time radio emission of SN 2000ft is therefore still being powered by its
interaction with the presupernova stellar wind, and not with the interstellar
medium (ISM). Indeed, the ram pressure of the presupernova wind is \rho_w v_w^2
\approx 7.6E-9 dyn/cm^2, at a supernova age of approximately 2127 days, which
is significantly larger than the expected pressure of the ISM around SN 2000ft.
At this age, the SN shock has reached a distance r_{sh \approx 0.06 pc, and our
observations are probing the interaction of the SN with dense material that was
ejected by the presupernova star about 5820 years prior to its explosion. From
our VLA monitoring, we estimate that the swept-up mass by the supernova shock
after about six years of expansion is \approx 0.29 M_sun, assuming an average
expansion speed of the supernova of 10000 km/s.
  We also searched for recently exploded core-collapse supernovae in our VLA
images. Apart from SN 2000ft (S_\nu \approx 1760 microJy at its peak,
corresponding to 1.1E28 erg/s/Hz, we found no evidence for any other radio
supernova (RSN) more luminous than \approx 6.0E26 erg/s/Hz, which suggests that
no other Type IIn SN has exploded since 2000 in the circumnuclear starburst of
NGC 7469.
