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Spatial correlation between submillimetre and Lyman-α galaxies in the SSA 22 protocluster


Lyman-α emitters are thought to be young, low-mass galaxies with ages of 108 yr (refs 1, 2). An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z ≈ 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster3,4. Galaxies that are bright at (sub)millimetre wavelengths are undergoing violent episodes of star formation5,6,7,8, and there is evidence that they are preferentially associated with high-redshift radio galaxies9, so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-α emitters) naturally arises. Here we report an imaging survey of 1,100-μm emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-α emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure.

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Figure 1: The positions of 1,100-μm sources and Lyα emitters towards the SSA 22 protocluster region.
Figure 2: Angular cross-correlation between submillimetre galaxies and Lyα emitters.


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We acknowledge T. Yamada and T. Hayashino for providing the Lyα emitter catalogue. We are grateful to H. Hirashita, T. Suwa, T. Kodama, M. Sameshima, M. Hayashi, T. T. Takeuchi and S. Komugi for discussions. We thank M. Uehara and the ASTE and AzTEC staff for their support. The ASTE project is led by Nobeyama Radio Observatory, in collaboration with the University of Chile, the University of Tokyo, Nagoya University, Osaka Prefecture University, Ibaraki University, and Hokkaido University. This work is based in part on archival data obtained with the NASA Spitzer Space Telescope.

Author Contributions K.N., Y.T., T. Takata, K.K. and R.K. designed and proposed the survey. Y.T., K.K., K.N., B.H., D.I. and T. Tosaki conducted the observing runs for two months. G.W.W., T.A.P., J.E.A. and K.S.S. developed the AzTEC instrument and the fundamental AzTEC reduction pipeline. H.E., D.H.H., I.A, T.O., N.Y. and K.T. contributed to the operation of AzTEC and ASTE during the survey. Y.T. and B.H. processed the raw AzTEC data, carried out simulations to create a source catalogue and computed the correlation functions. M.S.Y. and A.C. processed the Very Large Array 20-cm data. Y.M. provided the Lyα emitter catalogue and contributed to discussions, especially on Lyα emitters. All the authors discussed the results.

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Correspondence to Yoichi Tamura.

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Tamura, Y., Kohno, K., Nakanishi, K. et al. Spatial correlation between submillimetre and Lyman-α galaxies in the SSA 22 protocluster. Nature 459, 61–63 (2009).

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