Identifying potentially missed extended sources in the Fermi-LAT 4FGL Catalog using clustering analysis

Since its launch in 2008, the Large Area Telescope (LAT) has detected thousands of sources, many of which remain unassociated. Some may be extended sources represented in the catalog by multiple point-like entries. The reinterpretation of HESS J1813-178 as a single extended source motivates a systematic search for further missed extended sources. We search for clusters of unassociated -LAT sources and test whether single extended-source models describe them better than multiple catalog sources. We applied the algorithm called density-based spatial clustering of applications with noise (DBSCAN) to 4FGL sources with a linking scale of ɛ = 0.3^̧irc over 5, , we compared extended- and multiple-source models and characterized each candidate spectrally and morphologically, focusing on the Galactic plane. Each cluster contains at least one unassociated source and up to one extended or point-like associated source from selected categories, including pulsars, pulsar wind nebulae, and supernova remnants. Using Fermipy We identified 48 clusters containing 124 sources, each with at least one unassociated source. For all 8 clusters passing our quality selection, an extended-source model is statistically preferred. At linking scales of 0.4^̧irc and 0.5^̧irc, all 8 clusters retain their core sources. Cross-matches with the Second Fermi Galactic Extended Sources Catalog (2FGES) and the HESS Galactic Plane Survey (HGPS) showed that 5 clusters overlap known extended sources. The other 3 clusters, including one cluster with a morphology dependent on the interstellar emission model, have no counterpart in either catalog and are new extended-source candidates. Spatial clustering combined with likelihood-based model comparison can uncover extended sources missed in the -LAT catalog and complements existing searches.