We report \sim 2 \arcsec resolution Atacama Large Millimeter/submillimeter Array observations of the HCN ( 1–0 ) , HCO ^ { + } ( 1–0 ) , CO ( 1–0 ) , CO ( 2–1 ) , and CO ( 3–2 ) lines towards the nearby merging double-nucleus galaxy NGC 3256 .
We find that the high density gas outflow traced in HCN ( 1–0 ) and HCO ^ { + } ( 1–0 ) emission is co-located with the diffuse molecular outflow emanating from the southern nucleus , where a low-luminosity active galactic nucleus ( AGN ) is believed to be the dominant source of the far-infrared luminosity .
On the other hand , the same lines were undetected in the outflow region associated with the northern nucleus , whose primary heating source is likely related to starburst activity without obvious signs of AGN .
Both HCO ^ { + } ( 1–0 ) /CO ( 1–0 ) line ratio ( i.e .
dense gas fraction ) and the CO ( 3–2 ) /CO ( 1–0 ) line ratio are larger in the southern outflow ( 0.20 \pm 0.04 and 1.3 \pm 0.2 , respectively ) than in the southern nucleus ( 0.08 \pm 0.01 , 0.7 \pm 0.1 , respectively ) .
By investigating these line ratios for each velocity component in the southern outflow , we find that the dense gas fraction increases and the CO ( 3–2 ) /CO ( 1–0 ) line ratio decreases towards the largest velocity offset .
This suggests the existence of a two-phase ( diffuse and clumpy ) outflow .
One possible scenario to produce such a two-phase outflow is an interaction between the jet and the interstellar medium , which possibly triggers shocks and/or star formation associated with the outflow .