High-resolution spectroscopy of a young, low-metallicity optically-thin L = 0.02L* star-forming galaxy at z = 3.12

Vanzella, E., De Barros, S., Cupani, G., Karman, W., Gronke, M., Balestra, I., Coe, D., Mignoli, M., Brusa, M., Calura, F., Caminha, G. -B., Caputi, K., Castellano, M., Christensen, L., Comastri, A., Cristiani, S., Dijkstra, M., Fontana, A., Giallongo, E., Giavalisco, M., Gilli, R., Grazian, A., Grillo, C., Koekemoer, A., Meneghetti, M., Nonino, M., Pentericci, L., Rosati, P., Schaerer, D., Verhamme, A., Vignali, C. & Zamorani, G., 20-Apr-2016, In : Astrophysical Journal Letters. 821, 2, 7 p., 27.

Research output: Contribution to journalArticleAcademicpeer-review

  • E. Vanzella
  • S. De Barros
  • G. Cupani
  • W. Karman
  • M. Gronke
  • I. Balestra
  • D. Coe
  • M. Mignoli
  • M. Brusa
  • F. Calura
  • G. -B. Caminha
  • K. Caputi
  • M. Castellano
  • L. Christensen
  • A. Comastri
  • S. Cristiani
  • M. Dijkstra
  • A. Fontana
  • E. Giallongo
  • M. Giavalisco
  • R. Gilli
  • A. Grazian
  • C. Grillo
  • A. Koekemoer
  • M. Meneghetti
  • M. Nonino
  • L. Pentericci
  • P. Rosati
  • D. Schaerer
  • A. Verhamme
  • C. Vignali
  • G. Zamorani

We present VLT/X-Shooter and MUSE spectroscopy of a faint F814W = 28.60 +/- 0.33 (M-UV = -17.0), low-mass (less than or similar to 10(7)M(circle dot)), and compact (R-eff = 62 pc) freshly star-forming galaxy at z = 3.1169 magnified (16x) by the Hubble Frontier Fields galaxy cluster Abell S1063. Gravitational lensing allows for a significant jump toward lowluminosity regimes, in moderately high-resolution spectroscopy (R = lambda/d lambda similar to 3000-7400). We measured C IV lambda 1548, 1550, He II lambda 1640, OIII] lambda 1661, 1666, CIII]lambda lambda 1907, 1909, H beta, [O III] lambda lambda 4959, 5007 emission lines with FWHM less than or similar to 50 km s(-1) and (de-lensed) fluxes spanning the interval 1.0 x 10(-19)-2 x 10(-18) erg s(-1) cm(-2) at signal-to-noise ratio (S/N) = 4-30. The double-peaked Ly alpha emission with Delta v(red -blue) = 280(+/- 7) km s(-1) and delensed fluxes 2.4((blue))vertical bar 8.5((red)) x 10(-18) erg s(-1) cm(-2) (S/N = 38((blue))vertical bar 110((red)) indicate a low column density of neutral hydrogen gas consistent with a highly ionized interstellar medium as also inferred from the large [O III]lambda 5007/[O II] lambda 3727 > 10 ratio. We detect C IV lambda 1548, 1550 resonant doublet in emission, each component with FWHM less than or similar to 45 km s(-1) and redshifted by + 51(+/- 10) km s(-1) relative to the systemic redshift. We interpret this as nebular emission tracing an expanding optically thin interstellar medium. Both C IV lambda 1548, 1550 and He II lambda 1640 suggest the presence of hot and massive stars (with a possible faint active galactic nucleus). The ultraviolet slope is remarkably blue, beta = -2.95 +/- 0.20 (F-lambda = lambda(beta)), consistent with a dust-free and young less than or similar to 20 Myr galaxy. Line ratios suggest an oxygen abundance 12 + log(O/H) <7.8. We are witnessing an early episode of star formation in which a relatively low N-H I and negligible dust attenuation might favor a leakage of ionizing radiation. This galaxy currently represents a unique low-luminosity reference object for future studies of the reionization epoch with the James Webb Space Telescope.

Original languageEnglish
Article number27
Number of pages7
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 20-Apr-2016



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