Poster
D. A. D. Vaz
Abstract
Nearby, a subset of the earliest galaxies that persisted until the present day as relics of the early universe
offers a unique glimpse into the past. They are known as Ultra-Faint Dwarfs (UFDs).
These UFDs are essential objects to understand as they stand among the oldest galaxies known to exist
and have undergone minimal evolution since their formation. They are invaluable probes of the early
universe, shedding light on the early stages of galaxy formation and evolution. Moreover, they are
excellent laboratories for studying star formation and feedback in the feeblest halos. They are ideal for
placing constraints on dark matter models, given that dark accounts for up to 99% of their total mass.
They represent the extreme low-mass end of galaxy assembly. Within the cohort of UFDs, Leo T has
received considerable attention for a compelling reason: it is the faintest and least massive dwarf
galaxy known to contain neutral gas and exhibit signs of relatively recent star formation. This sets it
apart and positions Leo T as a natural ‘Rosetta stone’ for testing galaxy formation models, which have
struggled to reproduce Leo T-like galaxies until very recently.
In this contribution we show results of a study of Leo T that we have done by combining data from the
MUSE integral field spectrograph and photometric data from the HST. We have studied the age and
metallicity of the stars. We identify two populations of stars, all consistent with similar metallicity. Within
the young population sample, we discovered three emission line Be stars - a first for ultra-faint dwarfs.
The high sensitivity of MUSE allowed us to obtain velocity measurements for stars as faint as magnitude
~24, which allowed us to increase the number of Leo T stars observed spectroscopically from 19 to 75.
While looking for differences in the dynamics of young and old stars we find that they have different
kinematics, with the young population having a velocity dispersion consistent with the kinematics of
the cold component of the neutral gas. In this contribution we discuss these results and their
implications for the origin and evolution of Leo T.
Science with the Hubble and James Webb Space Telescopes VII: Stars, Gas & Dust in the Universe
Porto, Portugal
2024 April
