A dusty, normal galaxy in the epoch of reionization
Nature 519, 7543 (2015). doi:10.1038/nature14164
Authors: Darach Watson, Lise Christensen, Kirsten Kraiberg Knudsen, Johan Richard, Anna Gallazzi & Michał Jerzy Michałowski
Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7.
Five Solar System sights NASA should visit
Nature 519, 7543 (2015). http://www.nature.com/doifinder/10.1038/519274a
Author: Alexandra Witze
US planetary scientists dream up voyages of discovery, from Venus mappers to asteroid tours.
Crunch time for Canada’s role in mega-telescope
Nature 519, 7543 (2015). http://www.nature.com/doifinder/10.1038/519270a
Author: Alexandra Witze
Astronomers ask federal government to honour promise for Thirty Meter Telescope.
Highly efficient star formation in NGC 5253 possibly from stream-fed accretion
Nature 519, 7543 (2015). doi:10.1038/nature14218
Authors: J. L. Turner, S. C. Beck, D. J. Benford, S. M. Consiglio, P. T. P. Ho, A. Kovács, D. S. Meier & J.-H. Zhao
Gas clouds in present-day galaxies are inefficient at forming stars. Low star-formation efficiency is a critical parameter in galaxy evolution: it is why stars are still forming nearly 14 billion years after the Big Bang and why star clusters generally do not survive their births, instead dispersing to form galactic disks or bulges. Yet the existence of ancient massive bound star clusters (globular clusters) in the Milky Way suggests that efficiencies were higher when they formed ten billion years ago. A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. Here we report the detection of the J = 3→2 rotational transition of CO at the location of the massive cluster. The gas cloud is hot, dense, quiescent and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by the embedded star cluster. Its star-formation efficiency exceeds 50 per cent, tenfold that of clouds in the Milky Way. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.
Astronomy: Milky Way has corrugated rings
Nature 519, 7543 (2015). doi:10.1038/519265c
The Milky Way's stars sprawl outwards in a series of concentric ripples, hinting that it might extend farther into space than was thought.Data from the Sloan Digital Sky Survey confirm a previously known ring of stars at about 9,000 parsecs from the Sun. They