We present CO ( 3–2 ) emission observations toward the 3 ^ { \prime } \times 3 ^ { \prime } ( or 20 \times 20 kpc at a distance of 23 Mpc ) region of the southern barred spiral galaxy NGC 986 using the Atacama Submillimeter Telescope Experiment ( ASTE ) .
This effort is a part of our on-going extragalactic CO ( 3–2 ) imaging project ADIoS ( ASTE Dense gas Imaging of Spiral galaxies ) .
Our CO ( 3–2 ) image revealed the presence of a large ( the major axis is 14 kpc in total length ) gaseous bar filled with dense molecular medium along the dark lanes observed in optical images .
This is the largest “ dense-gas rich bar ” known to date .
The dense gas bar discovered in NGC 986 could be a huge reservoir of possible “ fuel ” for future starbursts in the central region , and we suggest that the star formation in the central region of NGC 986 could still be in a growing phase .
We found a good spatial coincidence between the overall distributions of dense molecular gas traced by CO ( 3–2 ) and the massive star formation depicted by H \alpha .
The global CO ( 3–2 ) luminosity L ^ { \prime } _ { CO ( 3 - 2 ) } of NGC 986 was determined to be ( 5.4 \pm 1.1 ) \times 10 ^ { 8 } K km s ^ { -1 } pc ^ { 2 } .
The CO ( 3–2 ) /CO ( 1–0 ) integrated intensity ratio was found to be 0.60 \pm 0.13 at a spatial resolution of 44 ^ { \prime \prime } or 5 kpc , and a CO ( 3–2 ) /CO ( 2–1 ) ratio was 0.67 \pm 0.14 at a beam size of \sim 25 ^ { \prime \prime } or \sim 2.8 kpc .
These line ratios suggest moderate excitation conditions of CO lines ( n _ { H _ { 2 } } \sim 10 ^ { 3 - 4 } cm ^ { -3 } ) in the central a few kpc region of NGC 986 .