Inhomogeneous Galactic Chemical Evolution: Modelling Ultra-Faint Dwarf Galaxies of the Large Magellanic Cloud

Kavli Affiliate: Alexander P. Ji

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| Summary:

Ultra-faint dwarf galaxies are among the oldest and most metal-poor galaxies
in the cosmos, observed to contain no traces of gas at the present time and a
high dark matter mass fraction. Understanding the chemical abundance dispersion
in such extreme environments could shed light on the properties of the first
generations of stars in the cosmos. We present a novel inhomogeneous chemical
evolution model, i-GEtool, that we apply to two ultra-faint dwarf galaxies,
Carina II (Car II) and Reticulum II (Ret II), which are satellites of the Large
Magellanic Cloud. In summary, our model is based on the Monte Carlo sampling of
the initial mass function as star formation proceeds in different gas cells of
the simulated galaxy volume. We account for the chemical enrichment of
Supernova bubbles as they spread in the interstellar medium, which causes
dispersion in the predicted elemental abundances. We recreate the elemental
abundance patterns by focusing on $alpha$- and odd-$textit{Z}$ elements,
predicting two sequences in [C/Fe] and [N/Fe] at all metallicities. Our models
systematically underestimate [C/Fe] and [Ti/Fe] because of the large
uncertainty in the adopted stellar nucleosynthesis yields. We discuss that the
observed C and N abundances had likely been affected by internal mixing
processes, which changed the initial surface abundances in the red giants. Our
Supernova feedback scheme is responsible for driving galactic outflows, which
quench the star formation activity in the simulated galaxies at early times.
The average outflow mass-loading factor as predicted by our models is $approx
10^{3}$, which extrapolates towards very low galaxy stellar masses the trend
observed at high stellar masses. Finally, by combining our model with the MIST
isochrone database, we draw synthetic colour-magnitude diagrams of Car II and
Ret II and compare them to observations.

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