Gas kinematics in FIRE simulated galaxies compared to spatially unresolved HI observations.

The shape of a galaxy's spatially unresolved, globally integrated 21-cm emission line depends on its internal gas kinematics: galaxies with rotationally supported gas discs produce double-horned profiles with steep wings, while galaxies with dispersion-supported gas produce Gaussian-like profiles with sloped wings. Using mock observations of simulated galaxies from the FIRE project, we show that one can therefore constrain a galaxy's gas kinematics from its unresolved 21-cm line profile. In particular, we find that the kurtosis of the 21-cm line increases with decreasing and that this trend is robust across a wide range of masses, signal-to-noise ratios, and inclinations.

The origin of the diverse morphologies and kinematics of Milky Way-mass galaxies in the FIRE-2 simulations.

We use hydrodynamic cosmological zoom-in simulations from the Feedback in Realistic Environments project to explore the morphologies and kinematics of 15 Milky Way (MW)-mass galaxies. Our sample ranges from compact, bulge-dominated systems with 90 per cent of their stellar mass within 2.5 kpc to well-ordered discs that reach ≳15 kpc.

Where are the most ancient stars in the Milky Way?

The oldest stars in the Milky Way (MW) bear imprints of the Galaxy's early assembly history. We use FIRE cosmological zoom-in simulations of three MW-mass disc galaxies to study the spatial distribution, chemistry, and kinematics of the oldest surviving stars ( ≳ 5) in MW-like galaxies. We predict the oldest stars to be less centrally concentrated at = 0 than stars formed at later times as a result of two processes.