UV Insights into the Complex Populations of M 87 Globular Clusters

摘要: We have imaged with HST's WFC3/UVIS the central 2.7$\times$2.7 arcmin$^2$ region of giant elliptical galaxy M 87, using ultraviolet filter F275W. In combination archival ACS/WFC data taken through F606W and F814W filters, covering same field, we constructed integrated-light UV-optical colors magnitudes for 1460 objects, most which are believed to be globular clusters belonging 87. The purpose was ascertain whether multiple-populations syndrome, ubiquitous among Galactic (GCs), exists also 87 family clusters. To achieve this goal, sought those GCs exceptionally blue UV-to-optical colors, because helium-enriched sub-populations produce a horizontal-branch morphology that is well populated at high effective temperature. For comparison, integrated, synthetic UV$-$optical purely optical been 45 GCs, starting from individual-star photometry obtained instruments filters. identify small group exhibiting radial color gradient, representing our best candidate hosting multiple populations extreme helium content. find spatial distribution bluer flattened in direction parallel jet, while redder more spherical. release astronomical community photometric catalog F275W, bands high-quality image stacks bands.