Formation of Ultra-diffuse galaxies in clusters

Using galaxy clusters from the TNG100 cosmological simulations we find that ultra-diffuse galaxies (UDGs) in clusters can have a dual origin: born-UDGs and tidal-UDGs, the latter formed by tidal disruption of more massive normal galaxies.

Different origins for the UDGs in clusters

UDGs are fascinating objects. With the typical stellar mass of dwarf galaxies (about M* ~ 1e8 Msun) but the sizes of a few kpc, UDGs are found in abundance in groups and clusters. How do these very extended dwarf galaxies form?

In our paper published in MNRAS we find that UDGs in cluster are a combination of two populations: normal low-surface brightness dwarfs from the field that happen to infall into the cluster and stop forming stars and also a sample of galaxies that underwent substantial tidal disruption where the mass content is more rapidly affected than the size, leaving a remnant with low surface brightnesses reminiscent of UDGs. We call these two samples “born-UDGs” and “tidal-UDGs”, respectively.

The dual origin is interesting because observations are starting to suggest that UDGs are not an homogeneous sample of objects (see for example their globular cluster contents, Lim et al. 2018). Our formation scenario in TNG100 makes clear predictions for born- and tidal-UDGs that may be observationally confirmed: tidal-UDGs are accreted earlier, they are more centrally concentrated within the cluster and have older stellar populations compared to born-UDGs. Also, tidal-UDGs have low velocity dispersions due to the tidal stripping, which may help explain some observed UDGs in the literature with low to little dark matter content.

You can check our article here

Check also some of our other awesome papers related to UDGs:

UDGs and their globular clusters in Virgo, Lim et al. 2020

UDGs and their globular clusters in Coma, Lim et al. 2018

Dark matter mass estimates of UDGs in Virgo, Toloba et al. 2018