Nuclear star formation activity and black hole accretion in nearby
  Seyfert galaxies
  Recent theoretical and observational works indicate the presence of a
correlation between the star formation rate (SFR) and the active galactic
nuclei (AGN) luminosity (and, therefore, the black hole accretion rate) of
Seyfert galaxies. This suggests a physical connection between the gas forming
stars on kpc scales and the gas on sub-pc scales that is feeding the black
hole. We compiled the largest sample of Seyfert galaxies to date with high
angular resolution (0.4-0.8 arcsec) mid-infrared (8-13 micron) spectroscopy.
The sample includes 29 Seyfert galaxies drawn from the AGN Revised Shapley-Ames
catalogue. At a median distance of 33 Mpc, our data allow us to probe nuclear
regions on scales of 65 pc (median value). We found no general evidence of
suppression of the 11.3 micron polycyclic aromatic hydrocarbon (PAH) emission
in the vicinity of these AGN, and used this feature as a proxy for the SFR. We
detected the 11.3 micron PAH feature in the nuclear spectra of 45% of our
sample. The derived nuclear SFRs are, on average, five times lower than those
measured in circumnuclear regions of 600 pc in size (median value). However,
the projected nuclear SFR densities are a factor of 20 higher than those
measured on circumnuclear scales. This indicates that the SF activity per unit
area in the central 65 pc of Seyfert galaxies is much higher than at larger
distances from their nuclei. We studied the connection between the nuclear SFR
and the black hole accretion rate and showed that numerical simulations
reproduce fairly well our observed relation.
