The warm molecular gas and dust of Seyfert galaxies: two different
  phases of accretion?
  The distribution of warm molecular gas (1000--3000 K), traced by the near-IR
H$_2$ 2.12 $\mu$m line, has been imaged with a resolution $<0.5$ arcsec in the
central 1 kpc of seven nearby Seyfert galaxies. We find that this gas is highly
concentrated towards the central 100 pc and that its morphology is often
symmetrical. Lanes of warm H$_2$ gas are observed only in three cases
(NGC\,1068, NGC\,1386 and Circinus) for which the morphology is much wider and
extended than the dust filaments. We conclude that there is no one-to-one
correlation between dust and warm gas. This indicates that, if the dust
filaments and lanes of warm gas are radial streaming motions of fuelling
material, they must represent \textit{two different phases of accretion}: the
dust filaments represent a colder phase than the gas close to the nucleus
(within $\sim$100 pc). We predict that the morphology of the nuclear dust at
these scales should resemble that of the cold molecular gas (e.g. CO at 10--40
K), as we show for CenA and NGC\,1566 by Atacama Large Millimeter/submillimeter
Array (ALMA) observations, whereas the inner H$_2$ gas traces a much warmer
phase of material identified with warmer (40-500 K) molecular gas such as
CO(6-5) or HCN (as shown by ALMA for NGC\,1068 and NGC\,1097). We also find
that X-ray heating is the most likely dominant excitation mechanism of the
H$_{2}$ gas for most sources.
