{
  "id": "1205.2693",
  "version": "v2",
  "published": "2012-05-11T20:00:00.000Z",
  "updated": "2016-11-30T00:36:14.000Z",
  "title": "The velocity dispersion and mass function of the outer halo globular cluster Palomar 4",
  "authors": [
    "Matthias J. Frank",
    "Michael Hilker",
    "Holger Baumgardt",
    "Patrick Côté",
    "Eva K. Grebel",
    "Hosein Haghi",
    "Andreas H. W. Küpper",
    "S. G. Djorgovski"
  ],
  "comment": "17 pages, accepted for publication in MNRAS; Fig. 8 surface brightness/density data at github.com/matthiasjfrank/pal4_surface_brightness",
  "doi": "10.1111/j.1365-2966.2012.21105.x",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "We obtained precise line-of-sight radial velocities of 23 member stars of the remote halo globular cluster Palomar 4 (Pal 4) using the High Resolution Echelle Spectrograph (HIRES) at the Keck I telescope. We also measured the mass function of the cluster down to a limiting magnitude of V~28 mag using archival HST/WFPC2 imaging. We derived the cluster's surface brightness profile based on the WFPC2 data and on broad-band imaging with the Low-Resolution Imaging Spectrometer (LRIS) at the Keck II telescope. We find a mean cluster velocity of 72.55+/-0.22 km/s and a velocity dispersion of 0.87+/-0.18 km/s. The global mass function of the cluster, in the mass range 0.55<=M<=0.85 M_solar, is shallower than a Kroupa mass function and the cluster is significantly depleted in low-mass stars in its center compared to its outskirts. Since the relaxation time of Pal 4 is of the order of a Hubble time, this points to primordial mass segregation in this cluster. Extrapolating the measured mass function towards lower-mass stars and including the contribution of compact remnants, we derive a total cluster mass of 29800 M_solar. For this mass, the measured velocity dispersion is consistent with the expectations of Newtonian dynamics and below the prediction of Modified Newtonian Dynamics (MOND). Pal 4 adds to the growing body of evidence that the dynamics of star clusters in the outer Galactic halo can hardly be explained by MOND.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2012-05-11T20:00:00.000Z",
      "comment": "17 pages, accepted for publication in MNRAS",
      "journal": null,
      "doi": null
    },
    {
      "version": "v2",
      "updated": "2016-11-30T00:36:14.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "outer halo globular cluster palomar",
      "mass function",
      "velocity dispersion",
      "remote halo globular cluster palomar",
      "precise line-of-sight radial velocities"
    ],
    "tags": [
      "journal article",
      "github project"
    ],
    "publication": {
      "doi": "10.1111/j.1365-2966.2012.21105.x",
      "journal": "J. Finance",
      "year": 2012,
      "month": "Jul",
      "volume": 423,
      "number": 3,
      "pages": 2917,
      "publisher": "Wiley-Blackwell"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1114397,
      "adsabs": "2012MNRAS.423.2917F"
    }
  }
}