July
2026
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2026ApJ..1005..224A
Authors
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Aziz, Hajar
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U, Vivian
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Aravindan, Archana
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Remigio, Raymond P.
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Canalizo, Gabriela
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Kader, Justin A.
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Bianchin, Marina
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Song, Yiqing
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Gao, Tianmu
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Rich, Jeff
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McGurk, Rosalie
Abstract
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We present the morphological, photometric, and spectroscopic properties of a z ∼ 1 galaxy, "lil gal," serendipitously detected in JWST Mid Infrared Instrument (MIRI) images of nearby galaxy VV 340. In the MIRI F560W and F770W images, we identify what appears to be a spiral galaxy with a central bulge. However, in the F1500W image, a second peak appears ∼0.″7 northwest (NW) from the central bulge, calling into question the nature of this source as a clumpy disk, a high-redshift interloper, or a galaxy merger. Multiband analyses of the three MIRI and four Hubble Space Telescope images suggest a photometric redshift of ∼0.92. Spectroscopic analyses of data from the Keck Near-Infrared Echellette Spectrometer (NIRES) reveal two sets of [N II] and Hα emission lines corresponding to the two observed sources. A redshift of z = 0.9248 is identified for the NW companion. Fainter emission lines are identified from the underlying galaxy at z = 0.9225, suggesting a merging galaxy pair at a projected separation of ∼5 kpc. From the emission line ratios from Keck NIRES and Keck Cosmic Web Imager spectra, we classify the system as hosting regions of active star formation, likely attributed to merger-induced starburst activity. The results demonstrate the necessity of resolved, spectroscopic follow-up analyses of galaxies found in deep JWST images to disentangle the role of galaxy mergers from clumpy disk galaxies at z ∼ 1 to cosmic noon and beyond.
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