Vol. 581
In section 4. Extragalactic astronomy

Planck's dusty GEMS: The brightest gravitationally lensed galaxies discovered with the Planck all-sky survey

The Planck satellite has done a submillimeter all-sky survey that is very useful for uncovering the exceptionally bright sources, which are gravitationally enhanced. Together with follow-up Herschel-SPIRE imaging that selects the high-redshift sources when they peak in the 350-500 micron bands, this work presents follow-up at IRAM in continuum and CO lines of 11 exceptionally bright far-infrared/submillimeter objects. The redshift of the sources ranges between z=2.2-3.6 from multiple lines obtained through a blind redshift search with EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA, along with optical/near-infrared imaging obtained at the CFHT and the VLT, show that they have the morphologies of strongly gravitationally lensed sources, including several giant arcs. Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850um and 2mm, respectively. Luminosities reach 2x10^14 Lsun (not corrected for the lensing effect). These exceptional sources must be caused essentially by starbursts and not AGN, as shown by additional WISE 22-um photometry and template fitting. Some sources are detected in radio at 1.4 GHz, with a flux ratio to infrared that is higher than expected from star formation, but that is attributed to the turbulent interstellar medium of these galaxies, rather than to the presence of radio AGN. The overall dust-to-gas ratios and star formation efficiencies of these exceptional sources are due to massive, metal-rich, intense, high-redshift starbursts.