{
  "id": "2003.13800",
  "version": "v1",
  "published": "2020-03-30T20:29:42.000Z",
  "updated": "2020-03-30T20:29:42.000Z",
  "title": "X-ray emission from He II 1640 emitting galaxies in VANDELS",
  "authors": [
    "A. Saxena",
    "L. Pentericci",
    "D. Schaerer",
    "R. Schneider",
    "R. Amorin",
    "A. Bongiorno",
    "A. Calabrò",
    "M. Castellano",
    "A. Cimatti",
    "F. Cullen",
    "A. Fontana",
    "J. P. U. Fynbo",
    "N. Hathi",
    "D. J. McLeod",
    "M. Talia",
    "G. Zamorani"
  ],
  "comment": "10 pages, 4 figures, submitted to MNRAS. Comments welcome!",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present X-ray measurements for 18 star-forming galaxies showing He II $\\lambda 1640$ emission at $z\\sim2.2-5$ in the Chandra Deep Field South, to test whether they show any X-ray excess compared to galaxies with no He II emission. Using aperture photometry on the 7 Ms Chandra image, we find that even though He II emitting galaxies in our sample (especially those with FWHM(He II) < 1000 km~s$^{-1}$) have marginally higher X-ray emission than galaxies with no He II, the difference is not statistically significant. The X-ray luminosity per star formation rate ($L_X$/SFR) for He II emitters and non-emitters are comparable, which rules out any enhanced contribution from young X-ray sources. The $L_X$/SFR at $z\\sim3$ for both He II emitters and non-emitters is consistent with observations at lower redshifts, and in line with the redshift evolution predicted by models. We also find that our $L_X$/SFR measurements are consistent with the metallicity dependence predicted and observed in the literature. Therefore, we conclude that there is no significant difference between the X-ray emission from galaxies with and without He II emission, which rules out enhanced contribution from XRBs or weak or obscured AGN in galaxies with strong He II at $z\\sim3$. Given the other similarities in the physical properties of both He II emitters and non-emitters reported earlier, alternative sources of He II ionising photon production, such as localised low-metallicity stellar populations, Pop-III stars, etc. may need to be explored.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-03-30T20:29:42.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "emitting galaxies",
      "chandra deep field south",
      "localised low-metallicity stellar populations",
      "young x-ray sources",
      "enhanced contribution"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 10,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}