Does SEGUE/SDSS indicate a dual galactic halo?

Ralph Schönrich, Martin Asplund, Luca Casagrande

    Research output: Contribution to journalArticlepeer-review

    35 Citations (Scopus)


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

    Original languageEnglish
    Article number7
    JournalAstrophysical Journal
    Issue number1
    Publication statusPublished - 1 May 2014


    Dive into the research topics of 'Does SEGUE/SDSS indicate a dual galactic halo?'. Together they form a unique fingerprint.

    Cite this