2011ApJ...732L..15C

The feedback from galactic outflows is thought to play an important role in shaping the gas content, star formation history, and ultimately the stellar mass function of galaxies. Here we present evidence for massive molecular outflows associated with ultra-luminous infrared galaxies (ULIRGs) in the co-added Redshift Search Receiver ¹²CO (1-0) spectrum. Our stacked spectrum of 27 ULIRGs at z = 0.043-0.11 (ν_rest= 110-120 GHz) shows broad wings around the CO line with ΔV(FWZI) ~ 2000 km/s. Its integrated line flux accounts for up to 25%±5% of the total CO line luminosity. When interpreted as a massive molecular outflow wind, the associated mechanical energy can be explained by a concentrated starburst with star formation rate (SFR) ≥ 100 M_☉/yr, which agrees well with their SFR derived from the FIR luminosity. Using the high signal-to-noise stacked composite spectrum, we also probe ¹³CO and ¹²CN emission in the sample and discuss how the chemical abundance of molecular gas may vary depending on the physical conditions of the nuclear region.