A new delivery route to Galactic Nuclei: Warm halo cloud impacts

Abstract

We propose a new mechanism for the delivery of gas to the heart of galactic nuclei. We show that warm halo clouds must periodically impact galactic centers and potentially deliver a large (~10^{4-6} M_{solar}) mass of gas to the galactic nucleus in a singular event. The impact of an accreting warm halo cloud originating far in the galactic halo can, depending on mixing, produce a nuclear starburst of low metallicity stars as well as low luminosity accretion onto the central black hole. Based on multiphase cooling around a LambdaCDM distribution of halos we calculate the nuclear impact rate, the mass captured by the central black hole and the fraction of active nuclei for impacting cloud masses in the range ~10^{4}-10^{6}M_{solar}. If there is moderate braking during cloud infall, our model predicts an average fraction of low luminosity active nuclei consistent with observations.Comment: 5 pages, 1 figure ApJL (accepted), uses emulateap