A proto-pseudobulge in ESO 320-G030 fed by a massive molecular inflow
  driven by a nuclear bar
  Galaxies with nuclear bars are believed to efficiently drive gas inward,
generating a nuclear starburst and possibly an active galactic nucleus (AGN).
We confirm this scenario for the isolated, double-barred, luminous infrared
galaxy ESO 320-G030 based on an analysis of Herschel and ALMA spectroscopic
observations. Herschel/PACS and SPIRE observations of ESO 320-G030 show
absorption/emission in 18 lines of H2O, which we combine with the ALMA H2O
423-330 448 GHz line (Eupper~400 K) and continuum images to study the nuclear
region. Radiative transfer models indicate that 3 nuclear components are
required to account for the H2O and continuum data. An envelope, with R~130-150
pc, T_dust~50 K, and N_H2~2x10^{23} cm^{-2}, surrounds a nuclear disk with R~40
pc and tau_100um~1.5-3 (N_H2~2x10^{24} cm^{-2}) and an extremely compact (R~12
pc), warm (~100 K), and buried (tau_100um>5, N_H2>~5x10^{24} cm^{-2}) core
component. The three nuclear components account for 70% of the galaxy L_IR
(SFR~16-18 Msun yr^{-1}). The nucleus is fed by a molecular inflow observed in
CO 2-1 with ALMA, which is associated with the nuclear bar. With decreasing
radius (r=450-225 pc), the mass inflow rate increases up to ~20 Msun yr^{-1},
which is similar to the nuclear SFR, indicating that the starburst is sustained
by the inflow. At lower r, the inflow is best probed by the far-infrared OH
ground-state doublets, with an estimated inflow rate of ~30 Msun yr^{-1}. The
short timescale of ~20 Myr for nuclear gas replenishment indicates quick
secular evolution, and indicates that we are witnessing an intermediate stage
(<100 Myr) proto-pseudobulge fed by a massive inflow that is driven by a strong
nuclear bar. We also apply the H2O model to the Herschel far-infrared
spectroscopic observations of H2^{18}O, OH, $^{18}OH, OH+, H2O^+, H3O^+, NH,
NH2, NH3, CH, CH^+, ^{13}CH^+, HF, SH, and C3, and estimate their abundances.
