What does a condition where $L_{ ext{UV}} ext{ extless extless} L_{ ext{IR}}$ strongly imply about current star formation?
A significant fraction of current star formation is deeply embedded in thick dust screens.
When comparing the luminosity observed in the Ultraviolet ($L_{ ext{UV}}$), which directly traces newly formed massive stars, against the total Infrared luminosity ($L_{ ext{IR}}$), which traces the re-radiated energy from dust, the ratio provides information about dust obscuration. If the UV output is much weaker than the total IR output ($L_{ ext{UV}} ext{ extless extless } L_{ ext{IR}}$), it signifies a major mismatch in energy accounting. This scenario strongly suggests that a vast majority of the light generated by the currently forming stars is being effectively captured and absorbed by dense screens of dust within the galaxy. This dust prevents the UV photons from escaping, forcing the energy to be reradiated in the IR, thereby severely underestimating the true SFR if only UV or $ ext{H} ext{ extalpha}$ measurements were used.
