A MegaCam Survey of Outer Halo Satellites. VI: The Spatially Resolved Star Formation History of the Carina Dwarf Spheroidal Galaxy

摘要: We present the spatially resolved star formation history (SFH) of Carina dwarf spheroidal galaxy, obtained from deep, wide-field g,r imaging and a metallicity distribution literature. Our photometry covers $\sim2$ deg$^2$, reaching up to $\sim10$ times half-light radius with completeness higher than $50\%$ at $g\sim24.5$, more one magnitude fainter oldest turnoff. This is first time combination depth coverage this quality has been used derive SFH Carina, enabling us trace its different populations unprecedented accuracy. find that Carina's consists two episodes well separated by temporal gap. These occurred old ($>10$ Gyr) intermediate ($2$-$8$ ages. measurements show episode comprises majority population, accounting for $54\pm5\%$ stellar mass within $1.3$ King tidal radius, while total derived $1.60\pm0.09\times 10^{6} M_{\rm{\odot}}$, mass-to-light ratio $1.8\pm0.2$. The consistent no recent which hints observed blue plume due stragglers. conclude evolved independently field Milky Way, since frequency duration events do not correlate orbital parameters. result supported age/metallicity relation in gradients calculated indicating outer regions are older metal poor.