Massive Clusters in the Inner Regions of NGC 1365: Cluster Formation and
  Gas Dynamics in Galactic Bars
  Cluster formation and gas dynamics in the central regions of barred galaxies
are not well understood. This paper reviews the environment of three 10^7 Msun
clusters near the inner Lindblad resonance of the barred spiral NGC 1365. The
morphology, mass, and flow of HI and CO gas in the spiral and barred regions
are examined for evidence of the location and mechanism of cluster formation.
The accretion rate is compared with the star formation rate to infer the
lifetime of the starburst. The gas appears to move from inside corotation in
the spiral region to looping filaments in the interbar region at a rate of ~6
Msun/yr before impacting the bar dustlane somewhere along its length. The gas
in this dustlane moves inward, growing in flux as a result of the accretion to
~40 Msun/yr near the ILR. This inner rate exceeds the current nuclear star
formation rate by a factor of 4, suggesting continued buildup of nuclear mass
for another ~0.5 Gyr. The bar may be only 1-2 Gyr old. Extrapolating the bar
flow back in time, we infer that the clusters formed in the bar dustlane
outside the central dust ring at a position where an interbar filament
currently impacts the lane. The ram pressure from this impact is comparable to
the pressure in the bar dustlane, and both are comparable to the pressure in
the massive clusters. Impact triggering is suggested. The isothermal assumption
in numerical simulations seems inappropriate for the rare fraction parts of
spiral and bar gas flows. The clusters have enough lower-mass counterparts to
suggest they are part of a normal power law mass distribution. Gas trapping in
the most massive clusters could explain their [NeII] emission, which is not
evident from the lower-mass clusters nearby.
