Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: José A. Benavides, Laura V. Sales, Mario. G. Abadi, Mark Vogelsberger, Federico Marinacci
| Summary:
We study the stellar properties of a sample of simulated ultra-diffuse
galaxies (UDGs) with stellar mass $M_star=10^{7.5}$ – $10^{9} ~
rm{M_{odot}}$, selected from the TNG50 simulation, where UDGs form mainly in
high-spin dwarf-mass halos. We divide our sample into star-forming and quenched
UDGs, finding good agreement with the stellar assembly history measured in
observations. Star-forming UDGs and quenched UDGs with $M_star geq 10^8; rm
M_odot$ in our sample are particularly inefficient at forming stars, having
$2$ – $10$ times less stellar mass than non-UDGs for the same virial mass halo.
These results are consistent with recent mass inferences in UDG samples and
suggest that the most inefficient UDGs arise from a late assembly of the dark
matter mass followed by a stellar growth that is comparatively slower (for
star-forming UDGs) or that was interrupted due to environmental removal of the
gas (for quenched UDGs). Regardless of efficiency, UDGs are $60%$ poorer in
[Fe/H] than the population of non-UDGs at a fixed stellar mass, with the most
extreme objects having metal content consistent with the simulated
mass-metallicity relation at $z sim 2$. Quenched UDGs stop their star
formation in shorter timescales than non-UDGs of similar mass and are, as a
consequence, alpha-enhanced with respect to non-UDGs. We identify metallicity
profiles in UDGs as a potential avenue to distinguish between different
formation paths for these galaxies, where gentle formation as a result of
high-spin halos would present well-defined declining metallicity radial
profiles while powerful-outflows or tidal stripping formation models would lead
to flatter or constant metallicity as a function of radius due
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