We report the discovery of a high-redshift , massive molecular outflow in the starburst galaxy SPT0346-52 ( z = 5.656 ) via the detected absorption of high-excitation water transitions ( H _ { 2 } O 4 _ { 2 , 3 } -4 _ { 1 , 4 } and H _ { 2 } O 3 _ { 3 , 0 } -3 _ { 2 , 1 } ) with the Atacama Large Millimeter/submillimeter Array ( ALMA ) .
The host galaxy is one of the most powerful starburst galaxies at high redshift ( star formation rate ; SFR \sim 3 , 600 M _ { \odot } year ^ { -1 } ) , with an extremely compact ( \sim 320 pc ) star formation region and a star formation rate surface density ( \Sigma _ { SFR } \sim 5 , 500 M _ { \odot } ~ { } year ^ { -1 } ~ { } kpc ^ { -2 } ) five times higher than ‘ maximum ’ ( i.e .
Eddington-limited ) starbursts , implying a highly transient phase .
The estimated outflow rate is \sim 500 M _ { \odot } year ^ { -1 } , which is much lower than the SFR , implying that in this extreme starburst the outflow capabilities saturate and the outflow is no longer capable of regulating star formation , resulting in a runaway process in which star formation will use up all available gas in less than 30 Myr .
Finally , while previous kinematic investigations of this source revealed possible evidence for an ongoing major merger , the coincidence of the hyper-compact starburst and high-excitation water absorption indicates that this is a single starburst galaxy surrounded by a disc .