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 or emission in 18 lines of H 2 O, which we combine with the ALMA H 2 O 4 23 − 3 30 448 GHz line (E upper ∼ 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 H 2 O and continuum data. An envelope, with radius R ∼ 130 − 150 pc, dust temperature T dust ≈ 50 K, and N H2 ∼ 2 × 10 23 cm −2 , surrounds a nuclear disk with R ∼ 40 pc that is optically thick in the far-infrared (τ 100 µm ∼ 1.5 − 3, N H2 ∼ 2 × 10 24 cm −2). In addition, an extremely compact (R ∼ 12 pc), warm (≈ 100 K), and buried (τ 100 µm > 5, N H2 5 × 10 24 cm −2) core component is required to account for the very high-lying H 2 O absorption lines. The three nuclear components account for 70% of the galaxy luminosity (SFR ∼ 16−18 M 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 tȯ M inf ∼ 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, ∼ 100 − 150 pc, the inflow is best probed by the far-infrared OH ground-state doublets, with an estimatedṀ inf ∼ 30 M yr −1. The inferred 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 H 2 O model to the Herschel far-infrared spectroscopic observations of H 18 2

CON-quest

“…In ESO 320-G030 (Fig. 2), however, it is clearly stronger on the redshifted side, possibly indicating that the absorbing gas is moving toward the nucleus, which is consistent with what is seen in CO J = 2−1 observations by González-Alfonso et al (2021). We note, however, that these asymmetries may also be due to lopsided distributions of material in the nucleus rather than noncircular motions.…”

Physics of ULIRGs with MUSE and ALMA: The PUMA project

“…We assumed a ULIRG-like factor, which is relatively low compared to the conversion factor used for normal galaxies (see e.g., Bolatto et al 2013). High nuclear column densities can produce self-absorbed CO(2-1) line profiles as seen in the compact nuclei of some local LIRGs (e.g., Sakamoto et al 2013; Pereira -Santaella et al 2017;González-Alfonso et al 2021). If the nuclear CO(2-1) emission of these ULIRGs is self-absorbed, the assumed ULIRG-like α CO conversion factor could result in underestimated Σ H 2 values.…”

Are local ULIRGs powered by AGN? The sub-kpc view of the 220 GHz continuum. PUMA II

“…We assumed a ULIRG-like factor, which is relatively low compared to the conversion factor used for normal galaxies (see e.g., Bolatto et al 2013). High nuclear column densities can produce self-absorbed CO(2-1) line profiles as seen in the compact nuclei of some local LIRGs (e.g., Sakamoto et al 2013, Pereira-Santaella et al 2017, González-Alfonso et al 2021. If the nuclear CO(2-1) emission of these ULIRGs is self-absorbed, the assumed ULIRG-like α CO conversion factor could result in underestimated Σ H 2 values.…”