On the nature and physical conditions of the luminous Ly alpha emitter CR7 and its rest-frame UV components

Research output: Contribution to journalJournal articleResearchpeer-review


  • sty2779

    Final published version, 10.8 MB, PDF document

  • David Sobral
  • Jorryt Matthee
  • Brammer, Gabriel
  • Andrea Ferrara
  • Lara Alegre
  • Huub Rottgering
  • Daniel Schaerer
  • Bahram Mobasher
  • Behnam Darvish

We present new Hubble Space Telescope (HST)/WFC3 observations and re-analyse VLT data to unveil the continuum, variability, and rest-frame ultraviolet (UV) lines of the multiple UV clumps of the most luminous Ly alpha emitter at z = 6.6, CR7 (COSMOS Redshift 7). Our re-reduced, flux-calibrated X-SHOOTER spectra of CR7 reveal an HeII emission line in observations obtained along the major axis of Ly alpha emission with the best seeing conditions. He II is spatially offset by approximate to+ 0.8 arcsec from the peak of Ly alpha emission, and it is found towards clump B. Our WFC3 grism spectra detects the UV continuum of CR7' s clump A, yielding a power law with beta = -2.5(-0.7) (+ 0.6) and M-UV = -21.87(-0.20) (+ 0.25) . No significant variability is found for any of the UV clumps on their own, but there is tentative (approximate to 2.2 sigma) brightening of CR7 in F110W as a whole from 2012 to 2017. HST grism data fail to robustly detect rest-frame UV lines in any of the clumps, implying fluxes less than or similar to 2 x 10(-17) erg s(-1) cm(-2) (3 sigma). We perform CLOUDY modelling to constrain the metallicity and the ionizing nature of CR7. CR7 seems to be actively forming stars without any clear active galactic nucleus activity in clump A, consistent with a metallicity of similar to 0.05-0.2 Z(circle dot). Component C or an interclump component between B and C may host a high ionization source. Our results highlight the need for spatially resolved information to study the formation and assembly of early galaxies.

Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Pages (from-to)2422-2441
Number of pages20
Publication statusPublished - Jan 2019
Externally publishedYes

    Research areas

  • galaxies: evolution, galaxies: high-redshift, galaxies: ISM, cosmology: observations, dark ages, reionization, first stars, early Universe, COLLAPSE BLACK-HOLE, CONTINUUM SLOPES, RADIO GALAXIES, NO EVIDENCE, TO 6-7, REIONIZATION, EPOCH, DUST, SPECTROSCOPY, EVOLUTION


Number of downloads are based on statistics from Google Scholar and www.ku.dk

No data available

ID: 245611907