{
  "id": "1707.03833",
  "version": "v1",
  "published": "2017-07-12T18:00:02.000Z",
  "updated": "2017-07-12T18:00:02.000Z",
  "title": "The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae",
  "authors": [
    "G. Iorio",
    "V. Belokurov",
    "D. Erkal",
    "S. E. Koposov",
    "C. Nipoti",
    "F. Fraternali"
  ],
  "comment": "submitted to MNRAS, \"comments welcome\"",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We exploit the first \\gaia data release to study the properties of the Galactic stellar halo as traced by RR Lyrae. We demonstrate that it is possible to select a pure sample of RR Lyrae using only photometric information available in the Gaia+2MASS catalogue. The final sample contains about 21600 RR Lyrae covering an unprecedented fraction ($\\sim60\\%$) of the volume of the Galactic inner halo ($\\text{R}<28$ kpc). We study the morphology of the stellar halo by analysing the RR Lyrae distribution with parametric and non-parametric techniques. Taking advantage of the uniform all-sky coverage, we test halo models more sophisticated than usually considered in the literature, such as those with varying flattening, tilt and/or offset of the halo with respect to the Galactic disc. A consistent picture emerges: the inner halo is well reproduced by a smooth distribution of stars settled on triaxial ellipsoids. The minor axis is perpendicular to the Milky Ways disc, while the major axis is misaligned by $\\sim20^{\\circ}$ from the Galactic Y axis. The elongation along the major axis is mild ($\\text{p}=1.27$), and the vertical flattening is shown to evolve from a squashed state with $\\text{q}\\approx0.57$ in the centre to a more spherical $\\text{q}\\approx0.75$ at the outer edge of our dataset. The density slope is well approximated by a single power-law with exponent $\\alpha=-2.96$. Within the range probed, we see no significant evidence for a change of the radial density slope, out of the plane tilt or an offset of the halo with respect to the Galaxy's centre.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-07-12T18:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "rr lyrae",
      "milky way stellar halo",
      "first all-sky view",
      "density slope",
      "major axis"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}