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Ultra-Diffuse Galaxies (UDGs) are some of the most remarkable galaxies in the Universe. They have been in the spotlight since 2015, when they were found by the dozens in the Coma cluster. These galaxies defy our understanding of natural evolutionary processes of low-mass galaxies, as they have the luminosities of dwarfs, but the sizes of giants. Several formation scenarios were proposed for UDGs, but none of them seems to fully explain all of the different kinds of UDGs found to date.
Ultra-Diffuse Galaxies (UDGs) are some of the most remarkable galaxies in the Universe. They have been in the spotlight since 2015, when they were found by the dozens in the Coma cluster. These galaxies defy our understanding of natural evolutionary processes of low-mass galaxies, as they have the luminosities of dwarfs, but the sizes of giants. Several formation scenarios were proposed for UDGs, but none of them seems to fully explain all of the different kinds of UDGs found to date.
Exploring the UDG universe using imaging
Exploring the UDG universe using imaging
Due to the faintness of UDGs, these galaxies are extremely hard to study with spectroscopy, making it hard to build up statistically meaningful samples of them. My research is devoted to developing tools to study UDGs using imaging and spectral energy distribution (SED) fitting. Through a sequence of works, we have shown that using imaging from the optical to the mid-infrared combined with Bayesian SED modelling routines, we can recover reliable stellar populations and structural parameters for UDGs. For more information, see Buzzo et al. 2022b.
Globular cluster (GC) content of UDGs as an indicator of their formation histories
Globular cluster (GC) content of UDGs as an indicator of their formation histories
Throughout the years, some UDGs have been shown to host unusually numerous GC systems for their stellar masses. In our work, we have found that the GC-richness of UDGs is correlated with their stellar populations. UDGs that have few-to-none GCs are young and metal-rich, while UDGs with a vast population of GCs show older and much more metal-poor populations. These findings make GC-poor UDGs consistent with the mass-metallicity scaling relation expected for regular dwarf galaxies. On the other hand, the GC-rich UDGs are found to be consistent with scaling relations of high-redshift galaxies, indicative of early-quenching. These results are discussed in details in Buzzo et al. 2022b and Buzzo et al. 2024 .
The multiple classes of Ultra-Diffuse Galaxies
The multiple classes of Ultra-Diffuse Galaxies
As mentioned previously, we found that a subsample of UDGs lies within the scatter of the mass-metallicity relation (MZR) for local classical dwarfs. However, another subsample is more metal-poor, being consistent with the evolving MZR at high-redshift. We investigate UDG positioning trends in the mass-metallicity plane as a function of surface brightness, effective radius, axis ratio, local volume density, mass-weighted age, star formation time-scale, globular cluster (GC) counts, and GC specific frequency. We find that there are multiple classes of UDGs. The first one comprises UDGs with lower stellar masses, prolonged star formation histories (SFHs), more elongated, inhabiting less dense environments, hosting fewer GCs, younger, consistent with the classical dwarf MZR, and fainter. The second contains UDGs with higher stellar masses, rapid SFHs, rounder, inhabiting the densest of our probed environments, hosting on average the most numerous GC systems, older, consistent with the high-redshift MZR (i.e. consistent with early-quenching), and brighter. The combination of these properties suggests that the first class of UDGs likely have dwarf progenitors, while the second class seems to have an early-quenching-like formation scenario.
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