The universal rotation curve of low surface brightness galaxies – IV. The interrelation between dark and luminous matter

Abstract

We apply the concept of spiral rotation curves universality [1] in order to investigate the properties of the baryonic and dark matter components of low surface brightness galaxies (LSB). The sample is composed by 72 objects, whose rotation curves are selected from literature. After a galaxies' division in five velocity bins according to their increasing optical velocity, we observe that in specifically normalized units the rotation curves are all alike in each selected velocity bin, i.e. it reflects the idea of the universal rotation curve (URC) found in Persic et al. [1]. From the mass modeling of our galaxies, we show that the dark matter component is dominant rather than the baryonic one, especially within the smallest and less luminous LSB galaxies. The Burkert profile results to be an optimal model fit for the dark matter halos and it is shown that the central surface density Σ0 ∼ 100 M pc −2 , similar to galaxies of different Hubble types and luminosities. Our analysis leads to a strong correlation between the structural properties of the dark and luminous matter. In particular, when we also evaluate the compactness for stars and dark matter, a strong correlation emerges between the stellar disc and dark matter halo. Finally, the introduction of the stellar compactness C * as a new parameter in the ballpark of the luminous matter besides the optical radius and the optical velocity improves the URC.

Dark Matters on the Scale of Galaxies

“…At last, only maximum disks can properly reproduce the observed ratio R ∼ 1.2 ± 0.2 between the corotation radius of barred galaxies and the semi-major axis of the bar; this value is the evidence that the corotation radius of barred galaxies is just beyond the end of the bar (e.g., [160]). However, the maximum-disk hypothesis only works for HSB galaxies; dwarf spheroidal and LSB galaxies appear to be dark-matter-dominated systems even in their innermost regions [161,162], although there are indications of a correlation between the distributions of the luminous and dark matter also in these systems [163].…”

Fundamental Properties of the Dark and the Luminous Matter from the Low Surface Brightness Discs

“…It is worth stressing a particular result emerging in the above works: the discrepancies between the individual and coadded RCs and the corresponding ones predicted from the URC via their V opt and R opt values are about at a level of 7%, a large part of which due to observational errors or to non-asymmetric motions present in the individual RCs. The URC results for LSBs [38] will be discussed in the next sections.…”

“…The spiral's best fit has a statistical uncertainty of 0.1 dex. Image reproduced from [38]. Figure 13.…”

“…The typical fractional observational uncertainties are 5% in V opt and 15% in R d , (see the right-down corner). Image reproduced from [38].…”

“…Radio synthesis observations show that these objects have very massive and very extended gaseous discs although with surface densities not higher than 5 M /pc 2 and M H I /L B ratios high up to ∼50 (e.g., [34]), with M H I the mass of the HI disc. Furthermore, inside their optical radius R opt , 1 LSBs are largely dominated by DM, as shown by the analysis of their: (1) Tully-Fisher relation (e.g., [35]), (2) individual (e.g., [36,37]) and stacked [38] rotation curves (RCs). Given their unique peculiarities that include: a very large extension, low surface densities in the stellar and gaseous disks so as in the 2-D projected DM surface density: 2 ∞ 0 ρ DM (R, z) dz, large amounts of DM and extremely low star formation rates, LSBs are very promising systems to help resolving the dark matter puzzle, being very different cosmic laboratories with respect to normal spirals, dwarf disks, and dwarf, normal, and giant ellipticals.…”