Intrinsic or instrumental origin of marginal extension in NGC4406, NGC4459, and NGC4526 at 144 MHz

Ascertain whether the LOFAR 144 MHz radio emission from the galaxies NGC4406, NGC4459, and NGC4526 is intrinsically extended (i.e., the sources are marginally resolved) or whether the apparent extension results from imaging smearing effects, thereby determining if these objects are truly point sources.

Background

Three galaxies (NGC4406, NGC4459, NGC4526) appear marginally extended in the LOFAR maps. The authors considered both intrinsic extension and possible smearing due to residual phase errors and finite time/frequency resolution.

After modeling and comparisons, their diagnostics do not conclusively classify these sources as point-like or resolved, and they label them as point-like to distinguish them from clearly resolved sources, leaving the intrinsic nature of their extension unresolved.