Extended Universal Rotational Curve of Spiral Galaxies

In this work, we aim to advance the Universal Rotation Curve (URC) paradigm by leveraging new data and extending its observational domain. Building on previous studies that established the URC using optical rotation curves reaching the galaxy optical radius Ropt , we exploit the SPARC sample’s extended HI rotation curves to construct the URC out to 2 Ropt . This crucial extension enables us to investigate the mass distribution of spiral galaxies in a region dominated by dark matter—an important step to better constrain galaxy mass models and to explore the nature of the dark matter particle. We find that the URC constructed from the SPARC sample’s extended HI rotation curves maintains its universal character out to 2 Ropt , with the double-normalized rotation curves collapsing onto a single profile. This extended URC provides new insights into the interplay between baryonic matter and dark matter in shaping galaxy rotation curves, particularly in the outer regions where dark matter dominates. Our results not only reinforce the URC paradigm but also refine our understanding of the mass distribution in spiral galaxies, offering new constraints on galaxy mass models and implications for the nature of dark matter.