Publication Date:
2014-10-26
Description:
We present deep spectroscopy of 17 very low mass ( M * ~= 2.0 10 6 –1.4 10 9 M ) and low luminosity ( M UV ~= –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 ], O iii ], C iv , Si iii ], C iii ]) which are rarely seen in individual spectra of more massive star-forming galaxies. C iii ] is detected in 16 of 17 low-mass star-forming systems with rest-frame equivalent widths as large as 13.5 Å. 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 (log U = –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 Lyα in z 6 galaxies, we suggest that C iii ] 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 .
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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