ACTIVE DISK BUILDING IN A LOCAL H I-MASSIVE LIRG: THE SYNERGY BETWEEN GAS, DUST, AND STAR FORMATION

HIZOA J0836-43 is the most Hi-massive (M-HI = 7.5 x 10(10) M-circle dot) galaxy detected in the HIPASS volume (delta = -90 degrees to + 25 degrees, nu < 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 similar to 130 kpc gas disk, with a total star formation rate (SFR) of similar to 20.5 M-circle dot 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-circle dot), the PAHs in HIZOA J0836-43 are more than twice as strong, whereas the warm dust continuum (lambda > 20 mu m) is best fit by a star-forming galaxy with L-TIR = 10(10) L-circle dot. Mopra CO observations suggest an extended molecular gas component (H-2+He > 3.7x10(9) M-circle dot) and a lower limit of similar to 64% for the gas-mass fraction; this is above average compared to local disk systems, but similar to that of z similar to 1.5 BzK galaxies (similar to 57%). However, the star formation efficiency (SFE = L-TR/L-CO(')) for HIZOA J0836-43 of 140 L-circle dot (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 similar to 1. This galaxy provides a rare opportunity in the nearby universe for studying (at z similar to 0.036) how disks were building and galaxies evolving at z similar to 1, when similarly large gas fractions were likely more common.