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A median redshift of 2.4 for galaxies bright at submillimetre wavelengths


A significant fraction of the energy emitted in the early Universe came from very luminous galaxies that are largely hidden at optical wavelengths (because of interstellar dust grains); this energy now forms part of the cosmic background radiation at wavelengths near 1 mm (ref. 1). Some submillimetre (submm) galaxies have been resolved from the background radiation2, but they have been difficult to study because of instrumental limitations3. This has impeded the determination of their redshifts (z), which is a crucial element in understanding their nature and evolution4. Here we report spectroscopic redshifts for ten submm galaxies that were identified using high-resolution radio observations5,6,7. The median redshift for our sample is 2.4, with a quartile range of 1.9–2.8. This population therefore coexists with the peak activity of quasars, suggesting a close relationship between the growth of massive black holes and luminous dusty galaxies8. The space density of submm galaxies at redshifts over 2 is about 1,000 times greater than that of similarly luminous galaxies in the present-day Universe, so they represent an important component of star formation at high redshifts.

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Figure 1: The ten spectra (aj) from Table 1 with identified redshifts from the sample of 34 submm galaxies observed, spanning the I = 22.2–26.4 range.
Figure 2: The redshift histogram of our submm galaxy sample (heavy cyan line).


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We thank C. Steidel, A. Shapley and T. Heckman for discussions. S.C.C. acknowledges support from NASA. I.R.S. acknowledges support from the Royal Society and a Philip Leverhulme Prize Fellowship. NRAO is operated by Associated Universities Inc., under a cooperative agreement with the US National Science Foundation. Data presented herein were obtained using the W. M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California and NASA. The Observatory was made possible by the financial support of the W. M. Keck Foundation.

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Chapman, S., Blain, A., Ivison, R. et al. A median redshift of 2.4 for galaxies bright at submillimetre wavelengths. Nature 422, 695–698 (2003).

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