{
  "id": "1606.01259",
  "version": "v1",
  "published": "2016-06-03T20:03:30.000Z",
  "updated": "2016-06-03T20:03:30.000Z",
  "title": "The Relation Between [OIII]/H$β$ and Specific Star Formation Rate in Galaxies at $z \\sim 2$",
  "authors": [
    "Claire Mackay Dickey",
    "Pieter van Dokkum",
    "Pascal Oesch",
    "Katherine Whitaker",
    "Ivelina Momcheva",
    "Erica Nelson",
    "Joel Leja",
    "Gabriel Brammer",
    "Marijn Franx",
    "Rosalind Skelton"
  ],
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Recent surveys have identified a seemingly ubiquitous population of galaxies with elevated [OIII]/H$\\beta$ emission line ratios at $z > 1$, though the nature of this phenomenon continues to be debated. The [OIII]/H$\\beta$ line ratio is of interest because it is a main component of the standard diagnostic tools used to differentiate between active galactic nuclei (AGN) and star-forming galaxies, as well as the gas-phase metallicity indicators $O_{23}$ and $R_{23}$. Here, we investigate the primary driver of increased [OIII]/H$\\beta$ ratios by median-stacking rest-frame optical spectra for a sample of star-forming galaxies in the 3D-HST survey in the redshift range $z\\sim1.4-2.2$. Using $N = 4220$ star-forming galaxies, we stack the data in bins of mass and specific star formation rates (sSFR) respectively. After accounting for stellar Balmer absorption, we measure [OIII]$\\lambda5007$\\AA/H$\\beta$ down to $\\mathrm{M} \\sim 10^{9.2} \\ \\mathrm{M_\\odot}$ and sSFR $\\sim 10^{-9.6} \\ \\mathrm{yr}^{-1}$, more than an order of magnitude lower than previous work at similar redshifts. We find an offset of $0.59\\pm0.05$ dex between the median ratios at $z\\sim2$ and $z\\sim0$ at fixed stellar mass, in agreement with existing studies. However, with respect to sSFR, the $z \\sim 2$ stacks all lie within 1$\\sigma$ of the median SDSS ratios, with an average offset of only $-0.06\\pm 0.05$. We find that the excitation properties of galaxies are tightly correlated with their sSFR at both $z\\sim2$ and $z\\sim0$, with a relation that appears to be roughly constant over the last 10 Gyr of cosmic time.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-06-03T20:03:30.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "specific star formation rate",
      "star-forming galaxies",
      "median sdss ratios",
      "standard diagnostic tools",
      "stellar balmer absorption"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}