Exploring Supermassive Black Hole Growth with ALMA

Massive tori with $\approx 10^{8-9}M_{\odot}$ are predicted to extend on$\sim $100 pc scale around the centre of elliptical galaxy progenitors by amodel of a supermassive black hole (SMBH) growth coeval to the spheroidalpopulation of the host galaxy. Direct detection of such massive tori would castlight on a key physical condition that allows the rapid growth of SMBHs and theappearance of QSOs at high redshift. For this reason, we examine thedetectability of such structures at substantial redshift with the Atacama LargeMillimeter Array (ALMA). We propose that submillimeter galaxies (SMGs) are thebest targets to test our predictions. In order to assess the observationalfeasibility, we estimate the expected number counts of SMGs with massive toriand check the detectability with the ALMA instrument, the unique facility whichcan resolve the central region of high redshift objects. Our work shows thatALMA will be able to resolve and detect high-$J$ ($J >$ 4) CO emissions from$\sim$100 pc scale extended massive tori up to $z\approx2$. Observations oflensed SMGs will yield excellent spatial resolution, allowing even to resolvetheir massive tori at higher redshift. We discuss further the detectability ofthe HCN molecule, as a better tracer of the high density gas expected in suchtori. The final goal of these kind of observations is to pinpoint possiblephysical mechanisms that storage in the very central galactic regions verylarge amount gas on timescale of several 10$^{8}$ yr.Comment: 22 pages, 5 figures, accepted for publication in Ap