Thesis topic: The origin of the blue stellar halos around Massive Group-Dominant Galaxies





Thesis Supervisors: Magda Arnaboldi, Johanna Hartke


The outermost stellar halos around the dominant galaxies in nearby massive groups are found to be very blue in colour. This measurement conflicts with the standard hierarchical mass assembly paradigm, since the current late-accretion models predict that the merging satellites that formed these extended halos were relatively massive, and hence, from the mass–metallicity relation, red, due to their relatively high metallicities. Thus, either these blue halos formed much earlier than predicted, or the late-accreted satellites have lower masses than expected from cosmological simulations. To distinguish between these possibilities, we carry out a study using the kinematics of planetary nebulae in these halos: late-accreted satellites leave tell-tale dynamical substructures at large radii that these observations are uniquely able to detect, even where they are photometrically invisible. This thesis requires active participation to the observations, data reduction and analysis.



Figure 1: Field of views for some of the group member galaxies to be studied in this thesis (M60, NGC 4365 and M105). The fields in red are to be surveyed with the Planetary Nebulae Spectrograph (PN.S) mounted on the William Herschel telescope on La Palma, and the whole Field of view with the wide field imager Megacam@CFHT on the Maunakea Observatory.