Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: Physical properties and implications for studies at z > 7

Daniel P. Stark, Johan Richard, Brian Siana, Stéphane Charlot, William R. Freeman, Julia Gutkin, Aida Wofford, Brant Robertson, Rahman Amanullah, Darach Watson, Bo Milvang-jensen

Research output: Contribution to journalArticle

106 Scopus citations


We present deep spectroscopy of 17 very low mass (M* ≃ 2.0 × 106-1.4 × 109 M) and low luminosity (MUV ≃-13.7 to -19.9) gravitationally lensed galaxies in the redshift range z ≃ 1.5-3.0. Deep rest-frame ultraviolet spectra reveal large equivalent width emission from numerous emission lines (N IV], OIII], CIV, Si III], CIII]) which are rarely seen in individual spectra of more massive star-forming galaxies. C III] is detected in 16 of 17 low-mass starforming systems with rest-frame equivalent widths as large as 13.5Å. Nebular C IV emission is present in the most extreme C III] emitters, requiring an ionizing source capable of producing a substantial component of photons with energies in excess of 47.9 eV. Photoionization models support a picture whereby the large equivalent widths are driven by the increased electron temperature and enhanced ionizing output arising from metal-poor gas and stars (0.04-0.13 Z), young stellar populations (6-50 Myr), and large ionization parameters (logU = -2.16 to -1.84). The young ages implied by the emission lines and continuum spectral energy distributions (SEDs) indicate that the extreme line emitters in our sample are in the midst of a significant upturn in their star formation activity. The low stellar masses, blue UV colours, and large specific star formation rates of our sample are similar to those of typical z ≳ 6 galaxies. Given the strong attenuation of Lya in z ≳ 6 galaxies, we suggest that CIII] is likely to provide our best probe of early star-forming galaxies with ground-based spectrographs and one off the most efficient means of confirming z ≳ 10 galaxies with the James Webb Space Telescope.

Original languageEnglish (US)
Pages (from-to)3200-3220
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Sep 5 2014



  • Cosmology: observations
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Stark, D. P., Richard, J., Siana, B., Charlot, S., Freeman, W. R., Gutkin, J., Wofford, A., Robertson, B., Amanullah, R., Watson, D., & Milvang-jensen, B. (2014). Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: Physical properties and implications for studies at z > 7. Monthly Notices of the Royal Astronomical Society, 445(3), 3200-3220. https://doi.org/10.1093/mnras/stu1618