Many new MW satellite galaxies have been discovered in the last few years, but some have been called into question by more sensitive imaging campaigns and most have only poorly constrained properties. CfA astronomer Nelson Caldwell was a member of a team that used the Magellan Clay telescope and the Megacam instrument to obtain images of four nearby dwarf galaxies probing nearly sixteen times fainter than previous measurements. The images reveal new stars and other objects, including extended structures, and enabled the astronomers to revise key parameters of these galaxies. One of the dwarfs, Sagittarius II, with a gas mass of only 1300 solar masses, is unusual in that it is small in size even for a dwarf galaxy and might instead be considered as the most extended globular cluster of stars for its brightness. Another, Reticulum II, is the most elongated dwarf galaxy known (nearly eight times longer than it is wide). A third, Tucana III, seems to be associated with a stream of material flowing into the MW and may be tidally disrupted. The sensitive new results were unable to measure any gas in any of the objects, but they set new limits, and will help astronomers make a more complete census of the Milky Way’s family of galaxies. Reference: “A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III” by Burçi̇n Mutlu-Pakdi̇l, David J. Sand, Jeffrey L. Carlin, Kristine Spekkens, Nelson Caldwell, Denija Crnojević, Allison K. Hughes, Beth Willman and Dennis Zaritsky, 7 August 2018, The Astrophysical Journal.DOI: 10.3847/1538-4357/aacd0e
