Canada-France-Hawaii Telescope | 2020 Sep 10
Astronomers have found that the key to understanding galaxies with "extreme" sizes, either small or large, may lie in their surroundings. In two related studies, an international team found that galaxies that are either "ultra-compact" or "ultra-diffuse" relative to normal galaxies of comparable brightness appear to reside in dense environments, i.e., regions that contain large numbers of galaxies. This has led the team to speculate that these "extreme" objects could have started out resembling normal galaxies, but then evolved to have unusual sizes through interactions with other galaxies.
- A wide field view of the central region of the Virgo Cluster, measuring 4.4 million light years on each side, from the Sloan Digital Sky Survey. Insets show deep images of two structurally extreme galaxies, taken with the MegaCam instrument on CFHT as part of the Next Generation Virgo Cluster Survey. An ultra-compact dwarf is within the crosshairs in the lower inset, while an ultra-diffuse galaxy is featured in the upper inset. Image credits: Sloan Digital Sky Survey, Canada-France-Hawaii Telescope and the NGVS team
The team identified both ultra-compact and ultra-diffuse galaxies as part of an unprecedented census of galaxies residing in the nearby Virgo cluster. The investigation used data from the Next Generation Virgo Cluster Survey (NGVS) obtained at the Canada-France-Hawaii Telescope (CFHT) using MegaCam, a wide-field, optical camera. At a distance of 50 million light years, Virgo is the galaxy cluster nearest to the Milky Way, and contains several thousand member galaxies, the majority of which are revealed, for the first time, in the NGVS data.
Astronomers discovered ultra-compact dwarf galaxies (UCDs) a quarter century ago, and they are the densest known galaxies in the Universe. Competing theories describe UCDs as either large star clusters, or as the remnants of larger galaxies that have been stripped of their stellar envelopes. ...
Ultra-diffuse galaxies (UDGs) are a mystery at the other end of the size spectrum. They are much larger, and more diffuse, than typical galaxies with similar brightness. Some theories suggest that UDGs are massive galaxies whose gas --- the fuel for their star formation --- was removed before many stars could form. Others suggest that they were once normal galaxies that have been made more diffuse through mergers and interactions. ...
The Next Generation Virgo Cluster Survey (NGVS). XXX.
Ultra-Diffuse Galaxies and Their Globular Cluster Systems ~ Sungsoon Lim et al
- Astrophysical Journal 899(1):69 (2020 Aug 10) DOI: 10.3847/1538-4357/aba433
- arXiv.org > astro-ph > arXiv:2007.10565 > 21 Jul 2020
Ultracompact Dwarf Galaxies in the Virgo Cluster ~ Chengze Liu et al