Structure and dynamics of giant low surface brightness galaxies

摘要

Giant low surface brightness (GLSB) galaxies are commonly thoughtto be massive, dark matter dominated systems. However, this conclusionis based on highly uncertain rotation curves. We present here a newstudy of two prototypical GLSB galaxies: Malin1 andNGC7589. We re-analysed existing H Iobservations andderived new rotation curves, which were used to investigate thedistributions of luminous and dark matter in these galaxies.In contrast to previous findings, the rotation curves of bothgalaxies show a steep rise in the central parts, typical of highsurface brightness (HSB) systems. Mass decompositions with a darkmatter halo show that baryons may dominate the dynamics of the innerregions. Indeed, a ``maximum disk'' fit gives stellar mass-to-lightratios 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 ofNGC7589 is reproduced well, whereas Malin1 represents achallenging test for the theory.Key words: dark matter - galaxies: structure - galaxies:kinematics and dynamics - galaxies: individual: Malin1 -galaxies: individual: NGC 7589 - methods: data analysis