The radio quiescence of active galaxies with high accretion rates

We present 6 cm Very Large Array observations of the Greene & Ho sample of 19 low-mass active galaxies with high accretion rates. This is one of the only studies of a uniform sample of narrow-line Seyfert 1 ( NLS1) galaxies with such high sensitivity and resolution. Although we detect only one source, the entire sample is very radio quiet down to strong limits. GH10 was found to have a radio power of 8.5 x 10(21) W Hz(-1) and a ratio R equivalent to f(6 cm)/f(4400) ((A) over circle) of 2.8. The 3 sigma upper limits for the remaining nondetections correspond to radio powers from 3 x 10(20) to 8 x 10(21) W Hz(-1) and 0.47 < R < 9.9. Stacking all nondetections yields an even stronger upper limit of R <= 0.27. An assessment of existing observations in the literature confirms our finding that NLS1s are consistently radio-quiet, with a radio-loud fraction of 0% - 6%, which is significantly lower than the 10% - 20% observed in the general quasar population. By analogy with stellar mass black holes, we argue that AGNs undergo a state transition at L-bol/L-Edd approximate to 0.01. Below this value a radiatively inefficient accretion flow effectively drives an outflow, which disappears when the flow turns into an optically thick, geometrically thin disk, or a radiation pressure - dominated slim disk at still higher L-bol/L-Edd.