SIMBAD references

We report on measurements of the disc central surface brightnesses (µ0) at 3.6µm for 438 galaxies selected by distance and absolute magnitude cutoffs from the 2350 plus galaxies in the Spitzer Survey of Stellar Structure in Galaxies, one of the largest and deepest homogeneous mid-infrared data sets of nearby galaxies. Our sample contains nearly three times more galaxies than the most recent study of the µ0 distribution. We demonstrate that there is a bimodality in the distribution of µ0. 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 µ0 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 discs. 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.