Action-space clustering of tidal streams to infer the galactic potential

Robyn E. Sanderson, Amina Helmi, David W. Hogg

    Research output: Contribution to journalArticle

    Abstract

    We present a new method for constraining the Milky Way halo gravitational potential by simultaneously fitting multiple tidal streams. This method requires three-dimensional positions and velocities for all stars to be fit, but does not require identification of any specific stream or determination of stream membership for any star. We exploit the principle that the action distribution of stream stars is most clustered when the potential used to calculate the actions is closest to the true potential. Clustering is quantified with the Kullback-Leibler Divergence (KLD), which also provides conditional uncertainties for our parameter estimates. We show, for toy Gaia-like data in a spherical isochrone potential, that maximizing the KLD of the action distribution relative to a smoother distribution recovers the input potential. The precision depends on the observational errors and number of streams; using K III giants as tracers, we measure the enclosed mass at the average radius of the sample stars accurate to 3% and precise to 20%-40%. Recovery of the scale radius is precise to 25%, biased 50% high by the small galactocentric distance range of stars in our mock sample (1-25 kpc, or about three scale radii, with mean 6.5 kpc). 20-25 streams with at least 100 stars each are required for a stable confidence interval. With radial velocities (RVs) to 100 kpc, all parameters are determined with 10% accuracy and 20% precision (1.3% accuracy for the enclosed mass), underlining the need to complete the RV catalog for faint halo stars observed by Gaia.

    Original languageEnglish (US)
    Article number98
    JournalAstrophysical Journal
    Volume801
    Issue number2
    DOIs
    StatePublished - Mar 10 2015

    Fingerprint

    stars
    radial velocity
    radii
    divergence
    halos
    confidence interval
    gravitational fields
    catalogs
    tracers
    tracer
    confidence
    recovery
    intervals
    estimates
    distribution
    method
    parameter

    Keywords

    • astrometry
    • dark matter
    • Galaxy: halo
    • Galaxy: kinematics and dynamics
    • Galaxy: structure

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    Action-space clustering of tidal streams to infer the galactic potential. / Sanderson, Robyn E.; Helmi, Amina; Hogg, David W.

    In: Astrophysical Journal, Vol. 801, No. 2, 98, 10.03.2015.

    Research output: Contribution to journalArticle

    Sanderson, Robyn E. ; Helmi, Amina ; Hogg, David W. / Action-space clustering of tidal streams to infer the galactic potential. In: Astrophysical Journal. 2015 ; Vol. 801, No. 2.
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