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5th of March 2021
ATCA and ALMA observations of Hyper Luminous Infrared Galaxies
by Riechers et al.
Hyper-luminous infrared galaxies (HyLIRGs) represent the most intensely star-forming galaxies through cosmic history. While rare at any epoch, they are particularly uncommon in the early universe, when structure formation had not yet matured sufficiently for such systems to exist. The star formation activity in HyLIRGs is typically driven by major mergers and commonly takes place in compact regions only a few kiloparsecs across, which contain intense radiation fields powered by newly-born massive stars. Riechers et al. report new observations of the hyper-luminous binary starburst ADFS-27 at z=5.655 using the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA), and the Hubble Space Telescope. A number of CO transitions are detected,together with spectral lines of H2O, OH+(11→01) and CH+. The 230GHz rest frame frequency of the CO(J=2→1) transition is redshifted (by the expansion of the Universe) to an observed frequency of 34.6GHz, which lies in the ATCA 7mm band.

The figure above shows, in black, the ALMA and ATCA broad-band spectrum of the line and continuum emission toward ADFS-27 (main panel), and CO spectral line profiles (inset). The Herschel/SPIRE spectrum of the nearby ultra-luminous infrared galaxy Arp 220, shifted to the observed frame of ADFS-27, is shown in gray for comparison. The detection of CO J=2→1 to 10→9 emission toward ADFS-27 reveals a massive, moderately highly excited molecular gas reservoir with a mass corresponding to about 25% of the stellar mass. The dynamical mass estimates suggest that ADFS-27 is consistent with a 1:1 merger of very massive galaxies that have comparable gas fractions, which at face value would suggest a similar evolutionary stage. More details are given in the paper, published in The Astrophysical Journal.

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