From kpcs to the central parsec of NGC 1097: Feeding star formation and a black hole at the same time

Abstract

A panchromatic view of the star-forming ring and feeding process in the central kpc of the galaxy NGC 1097 is presented. The assembled IR to UV images at ~10 pc resolution allow us to characterize the population of circa 250 clusters in the ring and disentangle the network of filaments of dust and gas that enshroud and feed them. The ring is a place of intermittent star bursts over the last 100 Myr. Four major episodes covering a proto-cluster phase of 11 mid-IR sources at the molecular clouds core, and two (three) previous bursts with a time separation of 20-30 Myr are identified. The extinction map of the inner few kpc resolves NGC 1097's two major dust lanes in bundles of narrow, <25 pc width, filaments running along the galaxy's bar. As they approach the ring, some circularize along it, others curve to the centre to produce a nuclear spiral. We believe these are kpc-scale dust-gas streamers feeding the ring and the black hole. The total mass in clusters formed in the ring in the last 100 Myr is < 107 M·, i.e. < 1 per cent of the 109 M· of molecular gas in the ring; yet, at its current star formation rate, ∼1.8 M· yr-1, an order of magnitude more in stellar mass should have been produced over that period. This means that the availability of gas in the ring is not the sole star formation driver, perhaps the rate at which dense gas accumulates in the ring is the key.