Does SEGUE/SDSS indicate a dual galactic halo?

摘要: We re-examine recent claims of observational evidence for a dual Galactic halo in SEGUE/SDSS data, and trace them back to improper error treatment neglect selection effects. In particular, the detection vertical abundance gradient can be explained as metallicity bias distance. A similar impact disk contamination affect sample blue horizontal branch stars. These examples highlight why non-volume complete samples require forward modeling from theoretical models or extensive bias-corrections. also show how uncertainties produce specific non-Gaussianity observed azimuthal velocity distribution stars, which erroneously identified two Gaussian components. single kinematic component yields an excellent fit when we model measurement process including distance uncertainties. Furthermore, that differences proper motion space are direct consequence cuts enhanced estimates less accurate. Thus, their presence is neither proof separate population nor measure reliability applied distances. conclude currently there no would favor over full substructure.