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Galaxies: Primeval twins

Nature Astronomy volume 1, Article number: 0054 (2017) Cite this article

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Spectroscopic and imaging data for low metallicity galaxies observed during the peak epoch of star formation offer detailed insights into the most distant galaxies discovered to date.

Galaxies observed within the first billion years of cosmic time (that is, at a redshift z ≳ 6) typically have properties that are quite distinct from those of star-forming galaxies at lower redshifts. These primeval galaxies commonly have very blue colours suggestive of negligible extinction by dust; very high rates of star formation per unit mass, suggesting rapid growth; low metallicity (less than 10% that of the Sun); small sizes; and extremely strong emission lines in the rest-frame ultraviolet and rest-frame optical5,7–9. Such systems are rare even just two billion years later, during the epoch when the global star formation rate density in the Universe reached its peak (z ≈ 2–3). Yet this later epoch offers the promise of a significantly higher signal-to-noise ratio and a wider rest-frame wavelength baseline for study. To identify lower-redshift analogues of primeval galaxies, Amorín and colleagues searched through a large spectroscopic survey of ∼2,000 galaxies at z ≈ 2–3 (ref. 10). They found and analysed ten rare galaxies whose rest-frame ultraviolet spectra showed the significant detection of multiple emission lines, which the authors consider the essential signature of an analogue for reionization-epoch galaxies. Detailed analysis of the HST images of these actively forming z ≈ 3 galaxies reveals a diversity of morphologies, ranging from close pairs (implying possible mergers), tadpole-like shapes with possible underlying disks, and irregular clumpy structures.

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Figure 1: Young stars and galaxy-scale outflows in distant galaxies.

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  1. Alice Shapley is in the Department of Physics and Astronomy at the University of California Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, California 90095, USA.,

    Alice Shapley

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  1. Alice Shapley
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Correspondence to Alice Shapley.

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Shapley, A. Galaxies: Primeval twins. Nat Astron 1, 0054 (2017). https://doi.org/10.1038/s41550-017-0054

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  • DOI: https://doi.org/10.1038/s41550-017-0054

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