Structure and dynamics of giant low surface brightness galaxies

TL;DR

This study re-analyzed rotation curves of two giant low surface brightness galaxies, revealing that their inner regions are dominated by baryons similar to high surface brightness galaxies, challenging previous dark matter dominance assumptions.

Contribution

The paper provides new rotation curves for Malin 1 and NGC 7589, showing their inner regions are baryon-dominated, and proposes a double-structure model for GLSB galaxies.

Findings

Inner regions show steep rotation curve rise, typical of HSB galaxies.

Baryons may dominate the inner dynamics, with stellar mass-to-light ratios similar to HSB galaxies.

NGC 7589's rotation curve fits MOND predictions, Malin 1 remains a challenge.

Abstract

Giant low surface brightness (GLSB) galaxies are commonly thought to be massive, dark matter dominated systems. However, this conclusion is based on highly uncertain rotation curves. We present here a new study of two prototypical GLSB galaxies: Malin 1 and NGC 7589. We re-analysed existing HI observations and derived new rotation curves, which were used to investigate the distributions of luminous and dark matter in these galaxies. In contrast to previous findings, the rotation curves of both galaxies show a steep rise in the central parts, typical of high surface brightness (HSB) systems. Mass decompositions with a dark matter halo show that baryons may dominate the dynamics of the inner regions. Indeed, a "maximum disk" fit gives stellar mass-to-light ratios in the range of values typically found for HSB galaxies. These results, together with other recent studies, suggest that GLSB galaxies are systems with a double structure: an inner HSB early-type spiral galaxy and an outer extended LSB disk. We also tested the predictions of MOND: the rotation curve of NGC 7589 is reproduced well, whereas Malin 1 represents a challenging test for the theory.