{
  "id": "1506.05495",
  "version": "v1",
  "published": "2015-06-17T21:01:48.000Z",
  "updated": "2015-06-17T21:01:48.000Z",
  "title": "Leo P: An Unquenched Very Low-Mass Galaxy",
  "authors": [
    "Kristen B. W. McQuinn",
    "Evan D. Skillman",
    "Andrew Dolphin",
    "John M. Cannon",
    "John J. Salzer",
    "Katherine L. Rhode",
    "Elizabeth A. K. Adams",
    "Danielle Berg",
    "Riccardo Giovanelli",
    "Léo Girardi",
    "Martha P. Haynes"
  ],
  "comment": "16 pages, 8 figures, 6 tables. Submitted to ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Leo P is a low-luminosity dwarf galaxy discovered through the blind HI Arecibo Legacy Fast ALFA (ALFALFA) survey. The HI and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with active star formation, an underlying older population, and an extremely low oxygen abundance. We have obtained optical imaging from the Hubble Space Telescope to study the evolution of Leo P. We refine the distance measurement to Leo~P to be 1.62+/-0.15 Mpc, based on the luminosity of the horizontal branch stars and 10 newly identified RR Lyrae candidates. This places the galaxy at the edge of the Local Group, ~0.4 Mpc from the loose association of dwarfs that includes Sextans A, Sextans B, Antlia, and NGC 3109. The star responsible for ionizing the HII region is most likely an O7V or O8V spectral type, with a stellar mass >25 Msun. The presence of this star provides observational evidence that massive stars at the upper-end of the initial mass function are capable of being formed at star formation rates as low as ~10^-5 Msun/yr. The best-fitting star formation history derived from the resolved stellar populations of Leo P using the latest PARSEC models shows a relatively constant star formation rate over the lifetime of the galaxy. The modeled luminosity characteristics of Leo P at early times are consistent with low-luminosity dSph Milky Way satellites, suggesting that Leo P is what a low-mass dSph would look like if it evolved in isolation and retained its gas. Despite the very low mass of Leo P, the imprint of reionization on its star formation history is subtle at best, and consistent with being totally negligible. The isolation of Leo P, and the total quenching of star formation of Milky Way satellites of similar mass, implies that local environment dominates the quenching of the Milky Way satellites.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-06-17T21:01:48.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "star formation history",
      "arecibo legacy fast alfa",
      "dsph milky way satellites",
      "hi arecibo legacy fast",
      "constant star formation rate"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}