Ultra-diffuse galaxy
An ultra-diffuse galaxy , UDG for short , is a large galaxy with a low surface brightness , more precisely with a surface brightness of less than 24 mag per square arc second , and with a half-light radius of more than 1.5 kilo parsec , which is an area of the order of magnitude corresponds to the Milky Way .
properties
In the course of systematic surveys , hundreds of ultra-diffuse galaxies have been found in nearby galaxy clusters . But there are also isolated UDGs, and a small number have been observed in low density groups .
Most of the ultra-diffuse galaxies are red and show no signs of star formation . The light profile drops exponentially from the center, and the mass is 100 million solar masses . For this relatively small mass, ultra-diffuse galaxies can show unexpectedly many globular clusters .
The metallicity corresponds to that of dwarf galaxies and is interpreted in such a way that a UDG does not contain several star generations.
Emergence
Several hypotheses are discussed regarding the formation of ultra-diffuse galaxies :
- These are fast rotating galaxies with low surface brightness
- The result of a gravitational interaction with other galaxies
- When the UDG passed through dense intergalactic medium , the interstellar material was removed from the galaxy, and the missing mass led to an expansion of the orbits of the remaining stars ( RAM pressure stripping ).
Dark matter
While some ultra-diffuse galaxies have a halo of dark matter like other galaxies, at least two UDGs show little signs at best: the orbits of the star clusters belonging to NGC1052-DF2 and NGC1052-DF4 are each completely covered by the visible baryonic matter of these Understand galaxies.
Individual evidence
- ^ Paul Bennet, David J. Sand, Dennis Zaritsky, Denija Crnojević, Kristine Spekkens, Ananthan Karunakaran: Evidence for Ultra-Diffuse Galaxy 'Formation' Through Galaxy Interactions . In: Astrophysics. Solar and Stellar Astrophysics . arxiv : 1809.01145v1 .
- ↑ Sungsoon Lim, Eric W. Peng, Patrick Cote, Laura V. Sales, Mark den Brok, John P. Blakeslee, Puragra Guhathakurta: The globular cluster system of ultra-Diffuse Galaxies in the Coma cluster . In: Astrophysics. Solar and Stellar Astrophysics . arxiv : 1806.05425v1 .
- ↑ Anna Ferre-Mateu et al .: Origins of ultra-diffuse galaxies in the Coma cluster II. Constraints from their stellar populations . In: Astrophysics. Solar and Stellar Astrophysics . arxiv : 1801.09695v2 .
- ↑ Pavel E. Mancera Piña, JAL Aguerri, Reynier Peletier, Aku Venhola, Scott Trager, Nelvy Choque Challapa: The evolution of ultra-diffuse galaxies in nearby galaxy clusters from the Kapteyn IAC WEAVE INT Clusters Survey . In: Astrophysics. Solar and Stellar Astrophysics . arxiv : 1901.07577v1 .
- ^ Pieter van Dokkum, Shany Danieli, Roberto Abraham, Charlie Conroy, Aaron J. Romanowsky: A second galaxy missing dark matter in the NGC1052 group . In: Astrophysics. Solar and Stellar Astrophysics . arxiv : 1901.05973v1 .