Distinguish distinct assembly histories from delayed merger growth in void galaxies

Determine whether the assembly history of massive void galaxies is intrinsically distinct over all cosmic time or merely delayed relative to galaxies outside voids, given that void galaxies eventually complete a comparable number of mergers.

Background

The paper finds that the most massive galaxies in deep cosmic underdensities are more compact than mass-matched field galaxies and that ongoing close-pair mergers are less common in voids. These observations are consistent with suppressed late-time merger-driven growth of extended stellar envelopes, particularly in massive, predominantly early-type central galaxies.

However, the paper also discusses simulation results indicating that void galaxies may eventually undergo a comparable total number of mergers to galaxies outside voids, with those mergers occurring later in cosmic time. Consequently, the observed compactness and lower present-day close-pair fraction do not establish whether void galaxies follow a fundamentally different cumulative assembly pathway or the same pathway with delayed timing. Resolving this distinction would clarify whether the environmental effect changes the complete merger history or primarily shifts its temporal progression.