Abstract
Context.
Low-ionization nuclear emission-line regions (LINERs) commonly host ionized gas outflows. Their role as high-energy particle accelerators is currently debated, especially following the recent very high-energy
γ
-ray detection of NGC 4278, which showed extreme radiative efficiencies that challenged standard shock-driven emission models.
Aims.
We aim to empirically determine the
γ
-ray radiative efficiency of a local sample of LINERs to test whether their high-energy emission can be powered by their extended ionized outflows or whether compact nuclear jets are required.
Methods.
We combined spatially resolved optical integral-field kinematics from the
Multi-Espectrógrafo en GTC de Alta Resolución para Astronomísa
at the Gran Telescopio de Canarias, yielding the kinetic powers of ionized outflows (
Ė
OF
), with 17 years of
Fermi
-Large Area Telescope observations to derive 0.05–500 GeV luminosities or 95% confidence upper limits. We constructed an optical/
γ
diagram placing our sample in the context of archetypal starbursts (M82, NGC 253) and radio galaxies (Centaurus A, M87).
Results.
We present the first empirical upper limits on the
γ
-ray radiative efficiency of LINER outflows as a population. Our likelihood analysis yields no formal detections (
TS
≥ 16) for the LINERs in our sample. The most physically constraining limit is found for the radio-loud LINER NGC 1052, where the maximum efficiency is restricted to
η
Fermi
-LAT upper limits generally lie well above the kinetic power of the ionized outflows (
η
≫ 100%). While three sources show marginal hints of emission (9 TS
Conclusions.
We conclude that the extended ionized outflows in LINERs are highly inefficient high-energy particle accelerators, analogous to starburst superwinds. These sample-level constraints demonstrate that extreme putative efficiencies cannot be sustained by the ionized outflows alone, favoring a compact nuclear jet origin for the most efficient
γ
-ray emitting LINERs.