Active Disk Building in a Local H I-massive LIRG: The Synergy Between Gas, Dust, and Star Formation

Abstract

HIZOA J0836-43 is the most Hi-massive (M_(Hi) = 7.5 × 10^(10)M_⊙) galaxy detected in the HIPASS volume (δ = −90◦ to + 25◦ , v <12,700 km s^(−1)) and lies optically hidden behind the Milky Way. Markedly different from other extreme Hi disks in the local universe, it is a luminous infrared galaxy (LIRG) with an actively star-forming disk (>50 kpc), central to its ~130 kpc gas disk, with a total star formation rate (SFR) of ~20.5M_⊙ yr^(−1). Spitzer spectroscopy reveals an unusual combination of powerful polycyclic aromatic hydrocarbon (PAH) emission coupled to a relatively weak warm dust continuum, suggesting photodissociation-region-dominated emission. Compared to a typical LIRG with similar total infrared luminosity (L_(TIR) = 10^(11) L_⊙), the PAHs in HIZOA J0836-43 are more than twice as strong, whereas the warm dust continuum (λ > 20 μm) is best fit by a star-forming galaxy with L_(TIR) = 10^(10) L_⊙. Mopra CO observations suggest an extended molecular gas component (H -2+He > 3.7×10^9 M_⊙ and a lower limit of ~64% for the gas-mass fraction; this is above average compared to local disk systems, but similar to that of z ~ 1.5 BzK galaxies (~57%). However, the star formation efficiency (SFE = L_(IR)/L'_(CO)) for HIZOA J0836-43 of 140 L_⊙ (K km s^(−1) pc^2)^(−1) is similar to that of local spirals and other disk galaxies at high redshift, in strong contrast to the increased SFE seen in merging and strongly interacting systems. HIZOA J0836-43 is actively forming stars and building a massive stellar disk. Its evolutionary phase of star formation (M_(stellar), SFR, and gas fraction) compared to more distant systems suggests that it would be considered typical at redshift z ~ 1. This galaxy provides a rare opportunity in the nearby universe for studying (at z ~ 0.036) how disks were building and galaxies evolving at z ~ 1, when similarly large gas fractions were likely more common.

Files

Additional details