Spatial origin of OH-absorbing gas

Resolve the spatial origin and characteristic scale of the OH-absorbing gas in infrared-bright galaxies using observations with sufficient angular resolution.

Background

The MeerKAT observations show OH absorption on scales ranging from roughly 0.5 to 10 kpc, but these sizes are upper limits imposed by the approximately 8-arcsec angular resolution. The observed velocity profiles generally agree with HCN profiles, suggesting that OH absorption and dense molecular-gas emission trace related nuclear kinematics.

The paper contrasts a central-kiloparsec interpretation with an alternative scenario in which the absorption arises in compact, approximately 10-pc circumnuclear disks or tori. The available data cannot distinguish between these possibilities, leaving the absorber’s exact spatial location unresolved.

References

These results suggest that OH absorption traces the bulk kinematics of nuclear molecular gas, while its exact spatial origin remains unresolved.

— OH Line Detections in Southern Galaxies of the IRAS Revised Bright Galaxy Sample  (2608.14473 - Zhao et al., 14 Aug 2026) in Section 4, subsection “Comparison with Previous Studies and Physical Interpretations of OH Line Detections in IR-bright Galaxies”