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. 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 or emission in 18 lines of H2O, which we combine with the ALMA H2O 4(23)-3(30) 448 GHz line (E-upper similar to 400 K) and continuum images to study the physical properties of the nuclear region. Radiative transfer models indicate that three nuclear components are required to account for the multi-transition H2O and continuum data. An envelope, with radius R similar to 130-150 pc, dust temperature T-dust approximate to 50 K, and N-H2 similar to 2x10(23) cm(-2), surrounds a nuclear disk with R similar to 40 pc that is optically thick in the far-infrared (tau (100 mu m)similar to 1.5-3, N-H2 similar to 2x10(24) cm(-2)). In addition, an extremely compact (R similar to 12 pc), warm (approximate to 100 K), and buried (tau (100 mu m)> 5, N-H2 greater than or similar to 5x10(24) cm(-2)) core component is required to account for the very high-lying H2O absorption lines. The three nuclear components account for 70% of the galaxy luminosity (SFR similar to 16-18 M-circle dot 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 M-inf similar to 20 M yr(-1), which is similar to the nuclear star formation rate (SFR), indicating that the starburst is sustained by the inflow. At lower r, similar to 100-150 pc, the inflow is best probed by the far-infrared OH ground-state doublets, with an estimated M-inf similar to 30 M yr(-1). The inferred short timescale of similar to 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 we estimate their abundances.