Astrophysics Colloquium by Joaquin Vieira (Caltech)

Abstract: The South Pole Telescope has systematically identified large numbers of high-redshift strongly gravitationally lensed systems. These sources are selected by their extreme mm flux, which is largely independent of redshift and lensing configuration. I will report results from the first blind redshift survey undertaken with the recently commissioned Atacama Large Millimeter Array (ALMA). We targeted 26 extraordinarily bright and dusty sources selected from a 2500 deg^2 mm survey conducted by the SPT and obtained redshifts via molecular carbon monoxide (CO) lines. We determine that roughly 40% of these sources lie at z>4, indicating that we have uncovered the missing high-redshift tail of starburst galaxies. Two sources are at z>5.6, placing them among the highest redshift starbursts known, and indicating that large reservoirs of dust can be present in massive galaxies at the end of the epoch of cosmic reionization. These sources were additionally targeted with high resolution imaging with ALMA, unambiguously demonstrating them to be strongly gravitationally lensed by foreground structure. We are undertaking a comprehensive and systematic followup campaign to use these ``cosmic magnifying glasses'' to study the infrared background in unprecedented detail, conduct detailed investigations of the properties of massive galaxies at z~1, inform the condition of the interstellar medium in starburst galaxies at high redshift, and place limits on dark matter substructure. I will discuss the scientific context and potential for these strongly lensed starburst galaxies, give an overview of our team's extensive followup efforts, and describe our preliminary science results.