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arXiv · 2604.19651

A Possible Protocluster of Galaxies Serendipitously Discovered in the Field of an Intermediate-Redshift Post-starburst Galaxy

Mary C. Knowlton·Justin S. Spilker·Rachel Bezanson·Vincenzo R. D'Onofrio·Anika Kumar·David J. Setton·Katherine A. Suess
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Abstract

We present the serendipitous discovery of an overdensity of submillimeter galaxies (SMGs) in the field of SDSSJ0909-0108, a massive z~0.7 post-starburst galaxy from the SQuIGGLE survey. ALMA observations at 870um and 2mm reveal six galaxies within a 35'' region with flux ratios consistent with emission from dust. Given the rarity of 870um sources and the small field-of-view of ALMA, we speculate that some of these sources are physically associated. None of the sources are at the same redshift as the post-starburst, and four do not have spectroscopic redshifts. We suggest that follow-up optical and/or ALMA observations be carried out to measure redshifts for the galaxies in this potential protocluster environment.

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Mary C. Knowlton, Justin S. Spilker, Rachel Bezanson, Vincenzo R. D'Onofrio, Anika Kumar, David J. Setton, Katherine A. Suess. 2026-04-21. A Possible Protocluster of Galaxies Serendipitously Discovered in the Field of an Intermediate-Redshift Post-starburst Galaxy. https://arxiv.org/abs/2604.19651

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