Program: GN-2015B-FT-30

We propose a pilot study for 5 massive dusty galaxies in the photometric redshift range of 1.6-2.5: they are classified as being quiescent (i.e. having suppressed star formation rate) from their UV-to-NIR colours, but are luminous in the Herschel FIR imaging implying high dust-obscured star formation rates (SFRs). Their discrepant SFRs motivate our proposed GNIRS spectroscopic follow-up to obtain independent Halpha SFR estimates. The proposed GNIRS spectroscopy will provide the necessary constraints to discern between the possible scenarios for the strong Herschel emission of these galaxies: (1) are they caught in a transition phase of < 200 Myr after a major starburst? (2) are they in fact star-forming galaxies that are misclassified because they follow an unconventional dust attenuation law, or have strong emission lines that bias their photometry? The GNIRS spectroscopic redshifts will be valuable for future ALMA follow-up. These peculiar galaxies present opportunities for new insights on most debated topics in galaxy evolution, e.g. star formation, quenching, and dust attenuation.