A DECam View of the Diffuse Dwarf Galaxy Crater II: The Colour-Magnitude Diagram
A.R. Walker, C.E. Mart\'inez-V\'azquez, M. Monelli, A.K. Vivas, G., Bono, C. Gallart, S. Cassisi, G. Andreuzzi, E.J. Bernard, M. Dall'Ora, G., Fiorentino, D.L. Nidever, K. Olsen, A. Pietrinferni, P.B. Stetson

TL;DR
This study presents a detailed colour-magnitude diagram of Crater II, revealing its old stellar population, star formation history, spatial distribution, and proper motion, providing insights into its evolution and properties.
Contribution
First deep CMD analysis of Crater II showing its old, bifurcated stellar populations and spatial inhomogeneities, with proper motion measurement from Gaia data.
Findings
Crater II's stars are predominantly old (~12.5 Gyr) with a secondary population (~10.5 Gyr).
The galaxy shows an elliptical shape with inhomogeneous star distribution.
Proper motion measured as approximately (-0.14, -0.10) mas/yr from Gaia DR2.
Abstract
We present a deep Blanco/DECam colour-magnitude diagram (CMD) for the large but very diffuse Milky Way satellite dwarf galaxy Crater II. The CMD shows only old stars with a clearly bifurcated subgiant branch (SGB) that feeds a narrow red giant branch. The horizontal branch (HB) shows many RR Lyrae and red HB stars. Comparing the CMD with [Fe/H] = -2.0 and [/Fe] = +0.3 alpha-enhanced BaSTI isochrones indicates a mean age of 12.5 Gyr for the main event and a mean age of 10.5 Gyr for the brighter SGB. With such multiple star formation events Crater II shows similarity to more massive dwarfs that have intermediate age populations, however for Crater II there was early quenching of the star formation and no intermediate age or younger stars are present. The spatial distribution of Crater II stars overall is elliptical in the plane of the sky, the detailed distribution shows a lack of…
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