Resolving the timing problem of the globular clusters orbiting the Fornax dwarf galaxy

G. W. Angus, A. Diaferio

    Research output: Contribution to journalArticle

    18 Citations (Scopus)

    Abstract

    We re-investigate the old problem of the survival of the five globular clusters (GCs) orbiting the Fornax dwarf galaxy in both standard and modified Newtonian dynamics (MOND). For the first time in the history of the topic, we use accurate mass models for the Fornax dwarf, obtained through Jeans modelling of the recently published line-of-sight (LOS) velocity dispersion data, and we are also not resigned to circular orbits for the GCs. Previously conceived problems stem from fixing the starting distances of the globulars to be less than half the tidal radius. We relax this constraint since there is absolutely no evidence for it and show that the dark matter (DM) paradigm, with either cusped or cored DM profiles, has no trouble sustaining the orbits of the two least massive GCs for a Hubble time almost regardless of their initial distance from Fornax. The three most massive globulars can remain in orbit as long as their starting distances are marginally outside the tidal radius. The outlook for MOND is also not nearly as bleak as previously reported. Although dynamical friction (DF) inside the tidal radius is far stronger in MOND, outside DF is negligible due to the absence of stars. This allows highly radial orbits to survive, but more importantly circular orbits at distances more than 85 per cent of Fornax's tidal radius to survive indefinitely. The probability of the GCs being on circular orbits at this distance compared with their current projected distances is discussed and shown to be plausible. Finally, if we ignore the presence of the most massive globular (giving it a large LOS distance), we demonstrate that the remaining four globulars can survive within the tidal radius for the Hubble time with perfectly sensible orbits.

    Original languageEnglish
    Pages (from-to)887-893
    Number of pages7
    JournalMonthly Notices of the Royal Astronomical Society
    Volume396
    Issue number2
    DOIs
    Publication statusPublished - Jun 2009

    Fingerprint

    dwarf galaxies
    globular clusters
    friction
    time measurement
    circular orbits
    radii
    orbits
    line of sight
    history
    dark matter
    modeling
    sustaining
    stems
    fixing
    histories
    stars
    profiles

    All Science Journal Classification (ASJC) codes

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

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    abstract = "We re-investigate the old problem of the survival of the five globular clusters (GCs) orbiting the Fornax dwarf galaxy in both standard and modified Newtonian dynamics (MOND). For the first time in the history of the topic, we use accurate mass models for the Fornax dwarf, obtained through Jeans modelling of the recently published line-of-sight (LOS) velocity dispersion data, and we are also not resigned to circular orbits for the GCs. Previously conceived problems stem from fixing the starting distances of the globulars to be less than half the tidal radius. We relax this constraint since there is absolutely no evidence for it and show that the dark matter (DM) paradigm, with either cusped or cored DM profiles, has no trouble sustaining the orbits of the two least massive GCs for a Hubble time almost regardless of their initial distance from Fornax. The three most massive globulars can remain in orbit as long as their starting distances are marginally outside the tidal radius. The outlook for MOND is also not nearly as bleak as previously reported. Although dynamical friction (DF) inside the tidal radius is far stronger in MOND, outside DF is negligible due to the absence of stars. This allows highly radial orbits to survive, but more importantly circular orbits at distances more than 85 per cent of Fornax's tidal radius to survive indefinitely. The probability of the GCs being on circular orbits at this distance compared with their current projected distances is discussed and shown to be plausible. Finally, if we ignore the presence of the most massive globular (giving it a large LOS distance), we demonstrate that the remaining four globulars can survive within the tidal radius for the Hubble time with perfectly sensible orbits.",
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    Resolving the timing problem of the globular clusters orbiting the Fornax dwarf galaxy. / Angus, G. W.; Diaferio, A.

    In: Monthly Notices of the Royal Astronomical Society, Vol. 396, No. 2, 06.2009, p. 887-893.

    Research output: Contribution to journalArticle

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    AU - Diaferio, A.

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