Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances

Vanzella, E., Castellano, M., Meneghetti, M., Mercurio, A., Caminha, G. B., Cupani, G., Calura, F., Christensen, L., Merlin, E., Rosati, P., Gronke, M., Dijkstra, M., Mignoli, M., Gilli, R., De Barros, S., Caputi, K., Grillo, C., Balestra, I., Cristiani, S., Nonino, M., Giallongo, E., Grazian, A., Pentericci, L., Fontana, A., Comastri, A., Vignali, C., Zamorani, G., Brusa, M., Bergamini, P. & Tozzi, P., 13-Jun-2017, In : The Astrophysical Journal. 842, 1, 10 p., 47.

Research output: Contribution to journalArticleAcademicpeer-review

  • E. Vanzella
  • M. Castellano
  • M. Meneghetti
  • A. Mercurio
  • G. B. Caminha
  • G. Cupani
  • F. Calura
  • L. Christensen
  • E. Merlin
  • P. Rosati
  • M. Gronke
  • M. Dijkstra
  • M. Mignoli
  • R. Gilli
  • S. De Barros
  • K. Caputi
  • C. Grillo
  • I. Balestra
  • S. Cristiani
  • M. Nonino
  • E. Giallongo
  • A. Grazian
  • L. Pentericci
  • A. Fontana
  • A. Comastri
  • C. Vignali
  • G. Zamorani
  • M. Brusa
  • P. Bergamini
  • P. Tozzi

We study the spectrophotometric properties of a highly magnified (mu similar or equal to 40-70) pair of stellar systems identified at z = 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint (m(UV) similar or equal to 30.6), young (less than or similar to 100 Myr), low-mass (<10(7) M-circle dot), low-metallicity (12 + Log(O/H) similar or equal to 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by similar or equal to 300 pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow (sigma(nu) less than or similar to 25 km s(-1)) high-ionization lines. These features may be the signature of very hot (T > 50,000 K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Ly alpha emission (e.g., C IV/Ly alpha > 15), despite the fact that the Ly alpha line flux is expected to be 150 times brighter (inferred from the H beta flux). A spatially offset, strongly magnified (mu > 50) Ly alpha emission with a spatial extent less than or similar to 7.6 kpc(2) is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Ly alpha induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with m(UV) > 34 de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Ly alpha emission-suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Ly alpha detection.

Original languageEnglish
Article number47
Number of pages10
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 13-Jun-2017


  • cosmology: observations, galaxies: formation, galaxies: high-redshift

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