We present the detection and morphological characterization of hot molecular gas outflows in nearby ultra-luminous infra-red galaxies ( ULIRGs ) , using the Spectrograph for Integral Field Observations in the Near Infrared ( SINFONI ) on the Very Large Telescope ( VLT ) .
We detect outflows observed in the 2.12 \mu m H _ { 2 } 1-0 S ( 1 ) line for three out of four ULIRGs that we analyzed , namely IRAS 12112+0305 , IRAS 14348-1447 , and IRAS 22491-1808 .
The outflows are mapped on scales of 0.7 - 1.6 kpc , show typical outflow velocities of 300 - 500 km s ^ { -1 } , and appear to originate from the nuclear region .
The outflows comprise hot molecular gas masses of M _ { H _ { 2 } ( hot ) } \sim 6 - 8 \times 10 ^ { 3 } M _ { \odot } .
Assuming a hot-to-cold molecular gas mass ratio of 6 \times 10 ^ { -5 } , as found in nearby luminous infrared galaxies , the total ( hot+cold ) molecular gas mass in these outflows is expected to be M _ { H _ { 2 } ( tot ) } \sim 1 \times 10 ^ { 8 } M _ { \odot } .
This translates into molecular mass outflow rates of Ṁ _ { H _ { 2 } ( tot ) } \sim 30 - 85 M _ { \odot } yr ^ { -1 } , which is a factor of a few lower than the star formation rate in these ULIRGs .
In addition , most of the outflowing molecular gas does not reach the escape velocity of these merger systems , which implies that the bulk of the outflowing molecular gas is re-distributed within the system and thus remains available for future star formation .
The fastest H _ { 2 } outflow is seen in the Compton-thick AGN of IRAS 14348-1447 , reaching a maximum outflow velocity of \sim 900 km s ^ { -1 } .
Another ULIRG , IRAS 17208-0014 , shows asymmetric H _ { 2 } line profiles different from the outflows seen in the other three ULIRGs .
We discuss several alternative explanations for the line asymmetries in this system , including a very gentle galactic wind , internal gas dynamics , low-velocity gas outside the disk , or two superposed gas disks .
We do not detect the hot molecular counterpart to the outflow previously detected in CO ( 2-1 ) in IRAS 17208-0014 , but we note that our SINFONI data are not sensitive enough to detect this outflow if it has a small hot-to-cold molecular gas mass ratio of \lesssim 9 \times 10 ^ { -6 } .