2016A&A...593L...2N

We present spatially resolved ALMA [CII] observations of the bright (flux density S₃₅₀=400mJy at 350µm), gravitationally lensed, starburst galaxy PLCK G045.1+61.1 at z=3.427, the "Garnet". This source is part of our set of "Planck's Dusty GEMS", discovered with the Planck's all-sky survey. Two emission-line clouds with a relative velocity offset of ∼600km/s extend towards north-east and south-west, respectively, of a small, intensely star-forming clump with a star-formation intensity of 220M_☉/yr/kpc², akin to maximal starbursts. [CII] is also seen in absorption, with a redshift of +350km/s relative to the brightest CO component. [CII] absorption has previously only been found in the Milky Way along sightlines toward bright high-mass star-forming regions, and this is the first detection in another galaxy. Similar to Galactic environments, the [CII] absorption feature is associated with [CI] emission, implying that this is diffuse gas shielded from the UV radiation of the clump, and likely at large distances from the clump. Since absorption can only be seen in front of a continuum source, the gas in this structure can definitely be attributed to gas flowing towards the clump. The absorber could be part of a cosmic filament or merger debris being accreted onto the galaxy. We discuss our results also in light of the on-going debate of the origin of the [CII] deficit in dusty star-forming galaxies.