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Published December 10, 2008 | Published
Journal Article Open

Molecular Gas in a Submillimeter Galaxy at z = 4.5: Evidence for a Major Merger at 1 Billion Years after the Big Bang


We report the detection of CO molecular line emission in the z = 4.5 millimeter-detected galaxy COSMOS J100054+023436 (hereafter J1000+0234) using the IRAM Plateau de Bure interferometer (PdBI) and NRAO's Very Large Array (VLA). The^12CO(4-3) line as observed with PdBI has a full line width of ~1000 km s^(−1), an integrated line flux of 0.66 Jy km s−1, and a CO luminosity of 3.2 × 10^10 L☉. Comparison to the 3.3 σ detection of the CO(2-1) line emission with the VLA suggests that the molecular gas is likely thermalized to the J = 4–3 transition level. The corresponding molecular gas mass is 2.6 × 10^(10) M☉ assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blueshifted line peaks and the line width a dynamical mass of 1.1 × 10^(11) M☉ is estimated assuming a merging scenario. The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5" from the previously detected Lyα emission. J1000+0234 exhibits very typical properties for lower redshift (z ~ 2) submillimeter galaxies (SMGs) and thus is very likely one of the long sought after high-redshift (z > 4) objects of this population. The large CO(4-3) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the big bang. Given its large star formation rate (SFR) of >1000 M☉ yr^(−1) and molecular gas content this object could be the precursor of a "red and dead" elliptical observed at a redshift of z = 2.

Additional Information

© 2008. The American Astronomical Society. Received 2008 September 11; accepted 2008 October 13; published 2008 October 29. E. S. would like to thank J. M. Winter and R. Neri for their great help during the visit of IRAM, Grenoble. E. S. thanks A. Weiß and E. F. Bell for helpful discussions. E. S. acknowledges the hospitality of the Aspen Center for Physics where the manuscript was prepared. C. C. thanks the Max-Planck- Gesellschaft and the Humboldt-Stiftung for support through the Max-Planck-Forschungspreis. The National Radio Astronomy Observatory (NRAO) is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.

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Published - Schinnerer2008p407Astrophys_J_Lett.pdf


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