Are X-Ray Detected Active Galactic Nuclei in Dwarf Galaxies Gamma-Ray Bright?

Abstract

The $\gamma$-ray emission from active galactic nuclei (AGN), including both beamed blazars and misaligned-AGN, dominates the extragalactic $\gamma$-ray point-source population count and flux. While multi-wavelength studies have detected an increasing number of AGN within dwarf galaxies in the local Universe, $\gamma$-ray emission has so far only been associated with systems hosting supermassive black holes (SMBHs). Dwarf-galaxy AGN are of particular interest because their central black holes fall in the intermediate-mass black hole (IMBH) regime, offering insight into the early evolution of SMBHs. Using 15~years of \textit{Fermi}-LAT data, we present the first search for $\gamma$-ray emission from dwarf-galaxy AGN. In the sample of 74 X-ray-selected dwarf-galaxy AGN, we find no sources that exceed the \textit{Fermi}-LAT detection threshold. However, a joint-likelihood analysis reveals a modest, trials-corrected population-level excess ($\sim2\sigma$) above blank-field expectations at very soft photon indices $\Gamma \gtrsim 3.8$ above 500~MeV. This hint is most pronounced when source contributions are weighed by $M^\alpha_{{\rm IMBH},i}/d_i^2$, with $\alpha\simeq1$--$1.5$, suggesting -- but not confirming -- that $\gamma$-ray emission could scale with the central black hole mass or a property correlated with it (e.g., accretion rate), but with a markedly softer spectrum than in SMBH-hosted AGN.