27 May: Toky Randriamampandry

Speaker: Toky Randriamampandry (University of Antananarivo, Madagascar)

Date: Wednesday 27 May 2026

Time: 15:00

Location: Physics 3.21 (Berry)

Resolved Neutral Hydrogen (HI) Kinematics and Dark Matter Distribution in the Era of Large HI Surveys

The discovery of flat rotation curves in spiral galaxies provided the first compelling evidence for dark matter halos. Yet discriminating between a "cuspy" halo—a natural prediction of cold dark matter—and a "cored" halo requires high-resolution rotation curves that extend well beyond the optical stellar disk. With the advent of large neutral hydrogen surveys such as the FAST Extended Atlas of Selected Targets Survey (FEASTS), the Widefield ASKAP L‑band Legacy All‑sky Blind surveY (WALLABY), the Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey, and the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey, we can now construct rotation curves for hundreds to thousands of galaxies, moving beyond the handful of bright, nearby systems that defined the classical picture.

In this talk, I will discuss recent progress in rotation curve decomposition and dark matter studies using large HI surveys. I will present results from the FEASTS project, focusing on extended high‑resolution rotation curves derived from combined interferometric and single‑dish observations. I will also address a major challenge facing deep neutral hydrogen surveys such as LADUMA, which is beam smearing. Using simulated observations of THINGS (The H I Nearby Galaxy Survey) galaxies projected to larger distances, I will demonstrate how spatial resolution strongly affects the recovery of galaxy kinematics, even when three‑dimensional fitting tools such as 3D‑BAROLO are used. These effects have important consequences for the interpretation of rotation curves and the reliability of dark matter constraints in distant galaxies.