  Leo T ($M_V = -8.0$) is both the faintest and the least massive galaxy known
to contain neutral gas and to display signs of recent star formation. We
analyse photometry and stellar spectra to identify member stars and to better
understand the overall dynamics and stellar content of the galaxy and to
compare the properties of its young and old stars. We use data from the Multi
Unit Spectroscopic Explorer (MUSE) on the VLT. We supplement this information
with spectroscopic data from the literature and with Hubble Space Telescope
(HST) photometry. Our analysis reveals two distinct populations of stars in Leo
T. The first population, with an age of $\lesssim 500~\mathrm{Myr}$, includes
three emission-line Be stars comprising 15% of the total number of young stars.
The second population of stars is much older, with ages ranging from
$>5~\mathrm{Gyr}$ to as high as $10~\mathrm{Gyr}$. We combine MUSE data with
literature data to obtain an overall velocity dispersion of $\sigma_{v} =
7.07^{+1.29}_{-1.12}~\mathrm{km\ s^{-1}}$ for Leo T. When we divide the sample
of stars into young and old populations, we find that they have distinct
kinematics. Specifically, the young population has a velocity dispersion of
$2.31^{+2.68}_{-1.65}\,\mathrm{km\ s^{-1}}$, contrasting with that of the old
population, of $8.14^{+1.66}_{-1.38}\,\mathrm{km\ s^{-1}}$. The fact that the
kinematics of the cold neutral gas is in good agreement with the kinematics of
the young population suggests that the recent star formation in Leo T is linked
with the cold neutral gas. We assess the existence of extended emission-line
regions and find none to a surface brightness limit of~$< 1\times
10^{-20}\,\mathrm{erg}\,\mathrm{s}^{-1}\,\mathrm{cm}^{-2}~\mathrm{arcsec}^{-2}$
which corresponds to an upper limit on star formation of $\sim
10^{-11}~\mathrm{M_\odot~yr^{-1}~pc^{-2}}$, implying that the star formation in
Leo T has ended.

Astrophysics of Galaxies