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Abstract

We present ALMA observations on and around the radio-quiet quasar UM 287 at z = 2.28. Together with a companion quasar, UM 287 is believed to play a major role in powering the surrounding enormous Lyα nebula (ELAN), dubbed the Slug ELAN, that has an end-to-end size of 450 physical kpc. In addition to the quasars, we detect a new dusty star-forming galaxy (DSFG), dubbed the Slug-DSFG, in 2 mm continuum with a single emission line consistent with CO(4−3). The Slug-DSFG sits at a projected distance of 100 kpc southeast from UM 287, with a systemic velocity difference of −360 ± 30 km s⁻¹ with respect to UM 287, suggesting it is a possible contributor to the powering of the Slug ELAN. With careful modeling of the SED and dynamical analyses, it is found that the Slug-DSFG and UM 287 appear low in both gas fraction and gas-to-dust ratio, suggesting environmental effects due to the host's massive halo. In addition, our Keck long-slit spectra reveal significant Lyα emissions from the Slug-DSFG, as well as a Lyα tail that starts at the location and velocity of the Slug-DSFG and extends toward the south, with a projected length of about 100 kpc. Supported by various analytical estimates we propose that the Lyα tail is a result of the Slug-DSFG experiencing ram pressure stripping. The gas mass stripped is estimated to be about 10⁹ M_⊙, contributing to the dense warm/cool gas reservoir that is believed to help power the exceptional Lyα luminosity.