A proto-pseudobulge in ESO 320-G030 fed by a massive molecular inflow driven by a nuclear bar
Abstract
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, Tdust~50 K, and NH2~2x1023 cm-2, surrounds a nuclear disk with R~40 pc and tau100um~1.5-3 (NH2~2x1024 cm-2) and an extremely compact (R~12 pc), warm (~100 K), and buried (tau100um>5, NH2>~5x1024 cm-2) core component. The three nuclear components account for 70% of the galaxy LIR (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 H218O, OH, $18OH, OH+, H2O+, H3O+, NH, NH2, NH3, CH, CH+, 13CH+, HF, SH, and C3, and estimate their abundances.