{
  "id": "1910.11877",
  "version": "v1",
  "published": "2019-10-25T18:00:01.000Z",
  "updated": "2019-10-25T18:00:01.000Z",
  "title": "Searching for z > 6.5 Analogs Near the Peak of Cosmic Star Formation",
  "authors": [
    "Xinnan Du",
    "Alice E. Shapley",
    "Mengtao Tang",
    "Daniel P. Stark",
    "Crystal L. Martin",
    "Bahram Mobasher",
    "Michael W. Topping",
    "Jacopo Chevallard"
  ],
  "comment": "21 pages, 9 figures, submitted to ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Strong [OIII]$\\lambda\\lambda$4959,5007+H$\\beta$ emission appears to be typical in star-forming galaxies at z > 6.5. As likely contributors to cosmic reionization, these galaxies and the physical conditions within them are of great interest. At z > 6.5, where Ly$\\alpha$ is greatly attenuated by the intergalactic medium, rest-UV metal emission lines provide an alternative measure of redshift and also constraints on the physical properties of star-forming regions and massive stars. We present the first statistical sample of rest-UV line measurements in z $\\sim$ 2 galaxies selected as analogs of those in the reionization era based on [OIII]$\\lambda\\lambda$4959,5007 EW or rest-frame U-B color. Our sample is drawn from the 3D-HST Survey and spans the redshift range 1.36 $\\leqslant$ z $\\leqslant$ 2.49. We find that the median Ly$\\alpha$ and CIII]$\\lambda\\lambda$1907,1909 EWs of our sample are significantly greater than those of z $\\sim$ 2 UV-continuum-selected star-forming galaxies. Measurements from both individual and composite spectra indicate a monotonic, positive correlation between CIII] and [OIII], while a lack of trend is observed between Ly$\\alpha$ and [OIII] at [OIII] EW < 1000$\\unicode{x212B}$. At higher [OIII] EW, extreme Ly$\\alpha$ emission starts to emerge. Using stacked spectra, we find that Ly$\\alpha$ and CIII] are significantly enhanced in galaxies with lower metallicity. Two objects in our sample appear comparable to z > 6.5 galaxies with exceptionally strong rest-UV metal line emission. These objects have significant CIV$\\lambda\\lambda$1548,1550, HeII$\\lambda$1640, and OIII]$\\lambda\\lambda$1661,1665 emission in addition to intense Ly$\\alpha$ or CIII]. Detailed characterization of these lower-redshift analogs provides unique insights into the physical conditions in z > 6.5 star-forming regions, motivating future observations of reionization-era analogs at lower redshifts.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2019-10-25T18:00:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cosmic star formation",
      "strong rest-uv metal line emission",
      "exceptionally strong rest-uv metal line"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 21,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}