Bimodality of Galaxy Disk Central Surface Brightness Distribution in the Spitzer 3.6 micron band

TL;DR

This study analyzes a large sample of nearby galaxies in the mid-infrared to reveal a clear bimodal distribution in their central surface brightness, indicating two stable galaxy modes dominated by dark matter or baryonic matter.

Contribution

It provides the first large-scale evidence of bimodality in galaxy disk central surface brightness at 3.6 microns, supporting the existence of two stable galaxy modes.

Findings

Bimodal distribution of mu0 in galaxy disks.

No intermediate surface brightness galaxies found.

Distribution not caused by observational biases or statistical fluctuations.

Abstract

We report on measurements of the disk central surface brightnesses (mu0) at 3.6 microns for 438 galaxies selected by distance and absolute magnitude cutoffs from the 2350+ galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G), one of the largest and deepest homogeneous mid-infrared datasets of nearby galaxies. Our sample contains nearly 3 times more galaxies than the most recent study of the mu0 distribution. We demonstrate that there is a bimodality in the distribution of mu0. Between the low and high surface brightness galaxy regimes there is a lack of intermediate surface brightness galaxies. Caveats invoked in the literature from small number statistics to the knowledge of the environmental influences, and possible biases from low signal to noise data or corrections for galaxy inclination are investigated. Analyses show that the bimodal distribution of mu0 cannot be due to any of these biases or statistical fluctuations. It is highly probable that galaxies settle in two stable modes: a dark matter dominated mode where the dark matter dominates at all radii - this gives birth to low surface brightness galaxies - and a baryonic matter dominated mode where the baryons dominate the dark matter in the central parts - this gives rise to the high surface brightness disks. The lack of intermediate surface brightness objects suggests that galaxies avoid (staying in) a mode where dark matter and baryons are co-dominant in the central parts of galaxies.