Physical origin of the low OH-emission detection rate

Determine why only a subset of infrared-luminous galaxies, particularly major galaxy mergers, host detectable OH megamaser activity.

Background

The survey finds that OH maser emission is concentrated primarily in LIRGs, while many LIRGs with strong radio continuum instead show OH absorption or no detectable OH emission. The authors discuss far-infrared pumping, dense molecular gas, and the possibility that different interstellar-medium conditions favor masing, absorption, or neither phenomenon.

Although these factors provide partial explanations, the paper emphasizes that the physical reason for the selective occurrence of OH megamasers remains unresolved. In particular, the authors note that the dense-gas ratio alone cannot account for the presence or absence of OH megamaser activity.

References

Despite extensive observational efforts, it remains unclear why only a subset of major galaxy mergers host OH megamasers.

— 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”