{
  "id": "2301.00017",
  "version": "v1",
  "published": "2022-12-30T19:00:00.000Z",
  "updated": "2022-12-30T19:00:00.000Z",
  "title": "Broad emission lines in optical spectra of hot dust-obscured galaxies can contribute significantly to JWST/NIRCam photometry",
  "authors": [
    "Jed McKinney",
    "Luke Finnerty",
    "Caitlin Casey",
    "Maximilien Franco",
    "Arianna Long",
    "Seiji Fujimoto",
    "Jorge Zavala",
    "Olivia Cooper",
    "Hollis Akins",
    "Alexandra Pope",
    "Lee Armus",
    "B. T. Soifer",
    "Kirsten Larson",
    "Keith Matthews",
    "Jason Melbourne",
    "Michael Cushing"
  ],
  "comment": "8 pages, 3 figures, 1 table, submitted to ApJL",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Selecting the first galaxies at z>7-10 from JWST surveys is complicated by z<6 contaminants with degenerate photometry. For example, strong optical nebular emission lines at z<6 may mimic JWST/NIRCam photometry of z>7-10 Lyman Break Galaxies (LBGs). Dust-obscured 3<z<6 galaxies in particular are potentially important contaminants, and their faint rest-optical spectra have been historically difficult to observe. A lack of optical emission line and continuum measures for 3<z<6 dusty galaxies now makes it difficult to test their expected JWST/NIRCam photometry for degenerate solutions with NIRCam dropouts. Towards this end, we quantify the contribution by strong emission lines to NIRCam photometry in a physically motivated manner by stacking 21 Keck II/NIRES spectra of hot, dust-obscured, massive ($\\log\\mathrm{M_*/M_\\odot}\\gtrsim10-11$) and infrared (IR) luminous galaxies at z~1-4. We derive an average spectrum and measure strong narrow (broad) [OIII]5007 and H$\\alpha$ features with equivalent widths of $130\\pm20$ A ($150\\pm50$ A) and $220\\pm30$ A ($540\\pm80$ A) respectively. These features can increase broadband NIRCam fluxes by factors of 1.2-1.7 (0.2-0.6 mag). Due to significant dust-attenuation ($A_V\\sim6$), we find H$\\alpha$+[NII] to be significantly brighter than [OIII]+H$\\beta$, and therefore find that emission-line dominated contaminants of high-z galaxy searches can only reproduce moderately blue perceived UV continua of $S_\\lambda\\propto\\lambda^\\beta$ with $\\beta>-1.5$ and z>4. While there are some redshifts (z~3.75) where our stack is more degenerate with the photometry of z>10 LBGs between $\\lambda_{rest}\\sim0.3-0.8\\,\\mu$m, redder filter coverage beyond $\\lambda_{obs}>3.5\\,\\mu$m and far-IR/sub-mm follow-up may be useful for breaking the degeneracy and making a crucial separation between two fairly unconstrained populations, dust-obscured galaxies at z~3-6 and LBGs at z>10.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-12-30T19:00:00.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "broad emission lines",
      "hot dust-obscured galaxies",
      "jwst/nircam photometry",
      "optical spectra",
      "contribute"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}