Astronomy

Signs of Old Age

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Science  29 May 2009:
Vol. 324, Issue 5931, pp. 1119
DOI: 10.1126/science.324_1119b

Researchers believe that most of the stars we see today were formed during short but very vigorous bursts in early dusty galaxies. Although the starlight emanating from these galaxies is concealed by dust, bright submillimeter emission, which traces dust heated by the ultraviolet light from newly formed stars, can be detected at great distances. Using data from a new submillimeter survey combined with radio, infrared, and optical observations, Coppin et al. found the most distant submillimeter galaxy yet detected: Its redshift of 4.76 suggests that intense star formation occurred in galaxies within 1 billion years of the Big Bang. In a different study, Cowie et al. used a submillimeter interferometer to determine an accurate position for HDF 850.1, a submillimeter galaxy discovered in 1998. Their data are not consistent with any previous optical identifications; no counterpart can be found even in the Hubble Deep Field, one of the deepest optical images available. Combined with information at other wavelengths, this result implies that HDF 850.1 is very distant, most probably characterized by a redshift greater than 4. Very few submillimeter galaxies have been confirmed at these high redshifts, but their absence could simply be the result of the observational difficulties involved in determining their positions. Both groups of authors suggest that galaxy formation models could be challenged if such galaxies proved to be more common than anticipated at early times in the history of the universe.

Mon. Not. R. Astron. Soc. 395, 1905 (2009); Astrophys. J. 697, L122 (2009).

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