The faint Universe
A myriad of galaxies have been discovered in the last decade thanks to the improvements in the telescope sensitives. Such galaxies have revealed and entirely new universe that was hidden due to their faintness.
The old and new-realm of early-type galaxies. The figure shows where the galaxies of the newly discovered families live in the size-luminosity diagram. cEs and UCDs follow as the natural extension of the low-mass ellipticals, whereas UDGs resemble more the dwarf regimes
Their location in the scaling relations are a good indicator of what type of early-type galaxy they could be, but it is unclear if they are intrinsic objects or if they are the result of external interactions. I have recently started to study how these faint galaxies form and what properties they have.
Compact elliptical galaxies
I have studied the possible mechanisms for the formation of compact elliptical galaxies (cE in the figure). using a sample of cEs with different environments and evolutionary stages, we find that the majority of our sample is consistent of being the stripped remnant of a larger and more massive galaxy. We do find, however, a few galaxies that are compatible with being the very low-mass end of the elliptical family, instead.
See:
'On the formation mechanisms of compact elliptical galaxies'; A. Ferre-Mateu, D. Forbes, A.J. Romanowsky, J. Janz, C. Dixon, Christoper; 2018, MNRAS, 473, 1819
Ultra-diffuse galaxies
UDGs have only been in the game for about 5 years, and thus their properties are still highly debated. They are thought to be either failed giants or simply a new type of dwarf. Unfortunately, their observations are very challenging and only a few galaxies have been studied so far. With new data from the 10.2m Keck telescope in Mauna Kea, Hawaii, we have studied the largest spectroscopic sample of UDGs in the Coma cluster, showing that they are mostly compatible with being a type of puffed dwarfs!
More data is on the way, so... Stay tuned!!!!
See:
'Origins of ultradiffuse galaxies in the Coma cluster - II: Constraints from their stellar populations'; A. Ferre-Mateu, A. Alabi, D. Forbes, A.J. Romanowsky, J. Brodie, V. Pandya, I. Martin-Navarro, S. Bellstedt, A. Wasserman, M. Stone and N. Okabe; 2018, MNRAS 479, 4891
'Origins of ultradiffuse galaxies in the Coma cluster - I: Constraints from their velocity phase space'; A. Alabi, A. Ferre-Mateu, A.J. Romanowsky, J. Brodie, D. Forbes, A. Wasserman, S. Bellstedt, I. Martin-Navarro, V. Pandya, M. Stone and N. Okabe; 2018, MNRAS, 479, 3308
'Extreme chemical abundance ratio suggesting an exotic origin for an ultradiffuse galaxy'; I. Martin-Navarro, A.J. Romanowsky, J. Brodie, A. Ferre-Mateu, A. Alabi, D. Forbes, M. Sharina, A. Villaume, V. Pandya, D. Martinez-Delgado; 2019, MNRAS, 484, 3425
Stellar population properties of Coma UDGs: ages, metallicities, alpha-enhancement (left panels) and star formation histories (right-top panel). They are all more similar to the properties of dwarf galaxies.
Bottom-right panel shows that the majority of these Coma UDGs are better explained with a late infall into the cluster, another clue to this dwarf-type origin.
