An ALMA view on the interstellar medium of the SPT sample of lensed high-redshift dusty galaxies

The South Pole Telescope unveiled a population of dusty, star-forming galaxies magnified by strong galaxy-galaxy lensing. We determined the redshift of 39 of these sources through ALMA millimeter spectroscopy and found a median redshift of 3.9 and a maximum of 5.8. An ongoing ALMA program targeting the reddest SPT sources should find even higher redshift. This sample of strongly magnified objects at high redshift offers a unique opportunity to study the cold interstellar medium (ISM) of distant galaxy. In addition, models predict that this population should contain a mix of starbursts and massive main-sequence galaxies. 

I will review the main results of the SPT collaboration about the properties of the ISM of these galaxies. Fine structure lines are also a very promising tracer of the ISM of these high-redshift objects. I will present a pilot study based on SPT2132-58 for which 3 fine-structure lines were detected ([NII], [CII] and [CI]. This extreme starburst at z=4.77 has an extremely short depletion timescale of 37 Gyr with a relatively mature ISM. Explaining the existence of so evolved galaxies at such high redshifts will by a stimulating challenge for galaxy evolution models.