Spectroscopic confirmation of a z = 6.740 galaxy behind the bullet cluster

Maruša Bradač, Eros Vanzella, Nicholas Hall, Tommaso Treu, Adriano Fontana, Anthony H. Gonzalez, Douglas Clowe, Dennis Zaritsky, Massimo Stiavelli, Benjamin Clément

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31 Scopus citations


We present the first results of our spectroscopic follow-up of 6.5 < z < 10 candidate galaxies behind clusters of galaxies.We report the spectroscopic confirmation of an intrinsically faint Lyman break galaxy (LBG) identified as a z850LP-band dropout behind the Bullet Cluster.We detect an emission line at λ = 9412 Å at>5σ significance using a 16 hr long exposure with FORS2 VLT. Based on the absence of flux in bluer broadband filters, the blue color of the source, and the absence of additional lines, we identify the line as Lyα at z = 6.740±0.003. The integrated line flux is f = (0.7±0.1±0.3)×10 -17 erg-1 s-1 cm-2 (the uncertainties are due to random and flux calibration errors, respectively) making it the faintest Lya flux detected at these redshifts. Given the magnification of μ = 3.0 ± 0.2 the intrinsic (corrected for lensing) flux is fint = (0.23 ± 0.03 ± 0.10 ± 0.02) × 10-17 erg-1 s-1 cm-2 (additional uncertainty due to magnification), which is ∼2-3 times fainter than other such measurements in z ∼ 7 galaxies. The intrinsic H 160W-band magnitude of the object is mint H160W = 27.57 ± 0.17, corresponding to 0.5L* for LBGs at these redshifts. The galaxy is one of the two sub-L* LBG galaxies spectroscopically confirmed at these high redshifts (the other is also a lensed z = 7.045 galaxy), making it a valuable probe for the neutral hydrogen fraction in the early universe.

Original languageEnglish (US)
Article numberL7
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Aug 10 2012


  • dark ages, reionization, first stars
  • galaxies: clusters: individual
  • galaxies: high-redshift
  • gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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