Abstract
Most massive galaxies are thought to have formed their dense stellar cores in early cosmic epochs1,2,3. Previous studies have found galaxies with high gas velocity dispersions4 or small apparent sizes5,6,7, but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we report a candidate core in the process of formation 11 billion years ago, at redshift z = 2.3. This galaxy, GOODS-N-774, has a stellar mass of 100 billion solar masses, a half-light radius of 1.0 kiloparsecs and a star formation rate of solar masses per year. The star-forming gas has a velocity dispersion of 317 ± 30 kilometres per second. This is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, which are compact quiescent galaxies at z ≈ 2 (refs 8, 9, 10, 11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 seem to be rare; however, from the star formation rate and size of this galaxy we infer that many star-forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.
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Support from STScI grant GO-1277 is acknowledged.
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E.N. obtained the data, led the analysis and the interpretation, and wrote the manuscript. P.v.D. contributed to the analysis and the interpretation. M.F. contributed to the interpretation. I.M. reduced the WFC3 imaging. G.B. and I.M. reduced the grism spectroscopy. K.W. and R.S. led the photometric analysis. All authors commented on the manuscript.
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Extended data figures and tables
Extended Data Figure 1 Linewidths of z ≈ 2 star-forming and quiescent galaxies.
The linewidth of GOODS-N-774 (open box) is among the highest measured for a normal star-forming galaxy at high redshift in Hα emission26,46 (light blue) or CO emission4 (SMGs; dark blue). The gas velocity dispersion is similar to the median stellar velocity dispersion of 304 km s−1 in a sample of quiescent galaxies at z = 1.5–2.2 with median mass of (refs 8, 9, 10, 11; red).
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Nelson, E., van Dokkum, P., Franx, M. et al. A massive galaxy in its core formation phase three billion years after the Big Bang. Nature 513, 394–397 (2014). https://doi.org/10.1038/nature13616
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DOI: https://doi.org/10.1038/nature13616
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