Dr. Dipanjan Mitra

How does a galaxy become a razor-thin needle, completely run out of fuel, and end up entirely alone in the cosmic wilderness? Standard galactic evolutionary models say this shouldn't happen, yet "Zangetsu" exists. Discovered lurking in the blinding glare of a nearby bright star within the HSC-SSP UltraDeep survey, Zangetsu is a newly unmasked Ultra Diffuse Galaxy (UDG) that shatters our understanding of low surface brightness systems. While most isolated dwarf galaxies are actively forming stars and possess irregular or round shapes, Zangetsu is a bizarre anomaly: it is completely quiescent, exceptionally red, and boasts a uniquely elongated, blade-like geometry (b/a ~ 0.25). In this talk, we will explore the observational wizardry required to extract this faint ghost from stellar scattered light, and confront the physics puzzle it presents. Internal mechanisms like supernova feedback fail to produce such extreme elongation, while external environmental stripping fails to explain its isolation. We will debate the two leading, radical scenarios for its origin: is Zangetsu a "backsplash" galaxy violently ejected from a past cluster collision, or the product of a rare, highly directional dwarf-dwarf merger?