We report the detection of far-IR CO rotational emission from the prototypical Seyfert 2 galaxy NGC 1068 .
Using Herschel-PACS , we have detected 11 transitions in the J _ { \mathrm { upper } } = 14 - 30 ( E _ { \mathrm { upper } } / k _ { B } = 580 - 2565 K ) range , all of which are consistent with arising from within the central 10 \arcsec ( 700 pc ) .
The detected transitions are modeled as arising from 2 different components : a moderate excitation ( ME ) component close to the galaxy systemic velocity , and a high excitation ( HE ) component that is blueshifted by \sim 80 km s ^ { -1 } .
We employ a large velocity gradient ( LVG ) model and derive { n _ { \mathrm { H } } } _ { 2 } \sim 10 ^ { 5.6 } cm ^ { -3 } , T _ { \mathrm { kin } } \sim 170 K , and { M _ { H } } _ { 2 } \sim 10 ^ { 6.7 } M _ { \odot } for the ME component , and { n _ { \mathrm { H } } } _ { 2 } \sim 10 ^ { 6.4 } cm ^ { -3 } , T _ { \mathrm { kin } } \sim 570 K , and { M _ { H } } _ { 2 } \sim 10 ^ { 5.6 } M _ { \odot } for the HE component , although for both components the uncertainties in the density and mass are \pm ( 0.6 - 0.9 ) dex .
Both components arise from denser and possibly warmer gas than traced by low- J CO transitions , and the ME component likely makes a significant contribution to the mass budget in the nuclear region .
We compare the CO line profiles with those of other molecular tracers observed at higher spatial and spectral resolution , and find that the ME transitions are consistent with these lines arising in the \sim 200 pc diameter ring of material traced by H _ { 2 } 1-0 S ( 1 ) observations .
The blueshift of the HE lines may also be consistent with the bluest regions of this H _ { 2 } ring , but a better kinematic match is found with a clump of infalling gas \sim 40 pc north of the AGN .
We consider potential heating mechanisms , and conclude that X-ray or shock heating of both components is viable , while far-UV heating is unlikely .
We discuss the prospects of placing the HE component near the AGN , and conclude that while the moderate thermal pressure precludes an association with the \sim 1 pc radius H _ { 2 } O maser disk , the HE component could potentially be located only a few parsecs more distant from the AGN , and might then provide the N _ { H } \sim 10 ^ { 25 } cm ^ { -2 } column obscuring the nuclear hard X-rays .
Finally , we also report sensitive upper limits extending up to J _ { \mathrm { upper } } = 50 , which place constraints on a previous model prediction for the CO emission from the X-ray obscuring torus .