{
  "id": "1010.0340",
  "version": "v1",
  "published": "2010-10-02T14:35:46.000Z",
  "updated": "2010-10-02T14:35:46.000Z",
  "title": "History and modes of star formation in the most active region of the Small Magellanic Cloud, NGC 346",
  "authors": [
    "M. Cignoni",
    "M. Tosi",
    "E. Sabbi",
    "A. Nota",
    "J. S. Gallagher"
  ],
  "comment": "17 pages. Accepted for publication in AJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We discuss the star formation history of the SMC region NGC 346 based on Hubble Space Telescope images. The region contains both field stars and cluster members. Using a classical synthetic CMD procedure applied to the field around NGC 346 we find that there the star formation pace has been rising from a quite low rate 13 Gyr ago to \\approx 1.4 \\times 10^{-8} Mo yr^{-1}pc^{-2} in the last 100 Myr. This value is significantly higher than in other star forming regions of the SMC. For NGC 346 itself, we compare theoretical and observed Color-Magnitude Diagrams (CMDs) of several stellar sub-clusters identified in the region, and we derive their basic evolution parameters. We find that NGC 346 experienced different star formation regimes, including a dominant and focused \"high density mode\", with the sub-clusters hosting both pre-main sequence (PMS) and upper main sequence (UMS) stars, and a diffuse \"low density mode\", as indicated by the presence of low-mass PMS sub-clusters. Quantitatively, the star formation in the oldest sub-clusters started about 6 Myr ago with remarkable synchronization, it continued at high rate (up to 2 \\times 10^{-5} Mo yr^{-1} pc^{-2}) for about 3 Myr and is now progressing at a lower rate. Interestingly, sub-clusters mainly composed by low mass PMS stars seem to experience now the first episode of star formation, following multi-seeded spatial patterns instead of resulting from a coherent trigger. Two speculative scenarios are put forth to explain the deficiency of UMS stars: the first invokes under-threshold conditions of the parent gas; the second speculates that the initial mass function (IMF) is a function of time, with the youngest sub-clusters not having had sufficient time to form more massive stars.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2010-10-02T14:35:46.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "star formation",
      "small magellanic cloud",
      "active region",
      "sub-clusters",
      "synthetic cmd procedure"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-6256/141/2/31",
      "journal": "The Astronomical Journal",
      "year": 2011,
      "month": "Feb",
      "volume": 141,
      "number": 2,
      "pages": 31
    },
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 871766,
      "adsabs": "2011AJ....141...31C"
    }
  }
}