Gaussian Random Field: Physical Origin of Sersic Profiles

TL;DR

This paper links the physical origin of Sersic galaxy profiles to Gaussian fluctuations in the cosmological density field, explaining different galaxy morphologies and predicting similar trends in galaxy clusters.

Contribution

It demonstrates that Gaussian density fluctuations naturally produce Sersic-like profiles and galaxy morphologies, connecting physical origin to observed galaxy structures.

Findings

Galaxies with steep central profiles have extended shallow outskirts.

Galaxies with shallow central profiles have steep outskirts.

Clusters of galaxies should show similar profile trends.

Abstract

While the Sersic profile family provide adequate fits for the surface brightness profiles of observed galaxies, the physical origin is unknown. We show that, if the cosmological density field are seeded by random gaussian fluctuations, as in the standard cold dark matter model, galaxies with steep central profiles have simultaneously extended envelopes of shallow profiles in the outskirts, whereas galaxies with shallow central profiles are accompanied by steep density profiles in the outskirts. These properties are in accord with those of the Sersic profile family. Moreover, galaxies with steep central profiles form their central regions in smaller denser subunits that possibly merge subsequently, which naturally leads to formation of bulges. In contrast, galaxies with shallow central profiles form their central regions in a coherent fashion without significant substructure, a necessary condition for disk galaxy formation. Thus, the scenario is self-consistent with respect to the correlation between observed galaxy morphology and Sersic index. We predict further that clusters of galaxies should display a similar trend, which should be verifiable observationally.