Are Gas-rich Ultra-diffuse Galaxies and Field Dwarfs Distinct?

Khadeejah Motiwala; Ananthan Karunakaran; Kristine Spekkens; Nikhil Arora; Arianna Di Cintio; Anna C. Wright; Dennis Zaritsky; Andrea V. Macciò

arXiv · 2502.14971

Are Gas-rich Ultra-diffuse Galaxies and Field Dwarfs Distinct?

Khadeejah Motiwala·Ananthan Karunakaran·Kristine Spekkens·Nikhil Arora·Arianna Di Cintio·Anna C. Wright·Dennis Zaritsky·Andrea V. Macciò

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Abstract

We explore the differences in gas-rich field Ultra-Diffuse Galaxies (UDGs) and classical dwarf galaxies using an extensive atomic gas (HI) follow-up survey of optically-selected UDG candidates from the Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) catalogue. We also compare the SMUDGes-HI observations with two state-of-the-art cosmological hydrodynamical simulations: Numerical Investigation of a Hundred Astrophysical Objects (NIHAO), where UDGs form through a series of bursty star formation episodes and Romulus25, in which UDGs occupy dark matter halos with high spins as a result of major mergers. Although the suggested formation scenarios for UDGs within these simulations are different, the present-day HI masses $M_{HI}$, stellar masses $M_*$, and star formation rates $SFR$ of simulated galaxies are qualitatively and quantitatively consistent with each other and with the observed SMUDGes-HI sample. We find that when controlling for $M_*$, there is a positive correlation between the gas richness $M_{HI}$/$M_*$ and the effective optical radius $R_{eff}$ , and that this trend is not different between the UDG and dwarf populations, within the measured scatter. Taken together, our results suggest that gas-rich, star-forming UDGs and dwarfs are not distinct galaxy populations, either observationally or in simulations.

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Khadeejah Motiwala, Ananthan Karunakaran, Kristine Spekkens, Nikhil Arora, Arianna Di Cintio, Anna C. Wright, Dennis Zaritsky, Andrea V. Macciò. 2025-02-20. Are Gas-rich Ultra-diffuse Galaxies and Field Dwarfs Distinct?. https://arxiv.org/abs/2502.14971

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