Connection between protoclusters and peculiar signpost galaxies

Determine the connection between protoclusters and the presence of peculiar galaxies such as radio galaxies, quasars, and other luminous signposts, and establish whether signpost-selected protocluster samples represent the full protocluster population.

Background

The paper explains that radio galaxies and quasars are commonly used as signposts for locating protoclusters because their high luminosities make them easy to identify and because they are expected to inhabit dense environments. However, the cited studies report no clear correlation between overdensity and the physical properties of radio galaxies, while other work suggests that quasar radiation may suppress star formation in nearby low-mass galaxies and that black-hole growth may depend primarily on host-galaxy stellar mass rather than environment.

These observations raise the possibility that successful protocluster searches based on active galactic nuclei or other peculiar galaxies may select only a subset of the broader protocluster population. The paper therefore identifies the relationship between protoclusters and such signpost galaxies, as well as the representativeness of signpost-selected samples, as unresolved.