{
  "id": "1604.06802",
  "version": "v1",
  "published": "2016-04-22T20:00:02.000Z",
  "updated": "2016-04-22T20:00:02.000Z",
  "title": "The FMOS-COSMOS survey of star-forming galaxies at z~1.6. IV: Excitation state and chemical enrichment of HII regions",
  "authors": [
    "D. Kashino",
    "J. D. Silverman",
    "D. Sanders",
    "J. S. Kartaltepe",
    "E. Daddi",
    "A. Renzini",
    "F. Valentino",
    "G. Rodighiero",
    "S. Juneau",
    "L. J. Kewley",
    "H. J. Zahid",
    "N. Arimoto",
    "T. Nagao",
    "J. Chu",
    "N. Sugiyama",
    "F. Civano",
    "O. Ilbert",
    "M. Kajisawa",
    "O. Le Fevre",
    "C. Maier",
    "M. Onodera",
    "A. Puglisi",
    "Y. Taniguchi",
    "COSMOS"
  ],
  "comment": "22 pages, 17 Figures, submitted to ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present results on the physical conditions of the interstellar medium of star-forming galaxies at 1.4<~z<~1.7 from the FMOS-COSMOS survey. We use a sample of 701 galaxies, for which the H$\\alpha$ emission line is detected, that represents the star-forming population over the stellar mass range 10^9.6<~M*/Msun<~10^11.6 with those at M*>10^11Msun being well sampled. The excitation state and chemical enrichment of the ionized gas are investigated using diagnostic diagrams based on the ratios of emission line strengths, including Alpha, [NII]6584, [SII]6717,6731, Hbeta, and [OIII]5007. Our data confirm an offset of the star-forming sequence on the BPT diagram ([OIII]/Hbeta vs. [NII]/Halpha), primarily towards higher [OIII]/Hbeta, compared with local star-forming galaxies. Based on the [SII] ratio, we measure an electron density (n_e=222^{+172}_{-128} cm^-3), higher than that of local galaxies. Overall, these changes in emission-line properties are due to a higher ionization parameter in high redshift galaxies as demonstrated by a lower than expected [SII]/Halpha ratio and a comparison to theoretical models. These results likely rule out an offset in the BPT diagram caused by a harder radiation field or AGN as assessed with Chandra. Finally, we revisit the mass-metallicity relation by using a conventional [NII]/Halpha-based indicator and a new calibration based on the [NII]/[SII] ratio introduced by Dopita et al. Consistent with our previous results, the most massive galaxies (M*>~10^11Msun) are fully enriched, while lower mass galaxies have metallicities considerably lower than local galaxies, in agreement with many studies. In addition, we show that the FMOS sample is inconsistent with a \"fundamental metallicity relation\", though well-fit with a physically-motivated model of galaxy evolution with gas regulation.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-04-22T20:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "star-forming galaxies",
      "excitation state",
      "chemical enrichment",
      "hii regions",
      "fmos-cosmos survey"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 22,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2016arXiv160406802K"
    }
  }
}