The Digital Press

Ultra-diffuse galaxies (UDGs) are not unusually large but follow expected size trends when linked to brightness and structure like other early-type galaxies. Their large sizes result from natural extensions of relations involving brightness, shape, and surface brightness.

Why it matters: Clarifies that UDG sizes fit established galaxy scaling relations, avoiding misconceptions about their nature.

The big picture: UDGs extend faint-end trends of early-type galaxies, linking size, brightness, and structural parameters smoothly.

The stakes: Misinterpreting UDG size-luminosity relations can lead to false claims about distinct galaxy types or formation processes.

Quick takeaway: Scatter in brightness and shape explains size variations; no evidence supports two separate UDG classes.