Clumpy Disk, Interloper, or Merger? Nature of a Distant Galaxy Pair at 5 kpc Projected Separation

Hajar Aziz; Vivian U; Archana Aravindan; Raymond P. Remigio; Gabriela Canalizo; Justin A. Kader; Marina Bianchin; Yiqing Song; Tianmu Gao; Jeff Rich; Rosalie McGurk

arXiv · 2606.21007

Clumpy Disk, Interloper, or Merger? Nature of a Distant Galaxy Pair at 5 kpc Projected Separation

Hajar Aziz·Vivian U·Archana Aravindan·Raymond P. Remigio·Gabriela Canalizo·Justin A. Kader·Marina Bianchin·Yiqing Song·Tianmu Gao·Jeff Rich·Rosalie McGurk

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Abstract

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. Multi-band analyses of the three MIRI and four Hubble Space Telescope (HST) 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 H-alpha 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 (KCWI) 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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Hajar Aziz, Vivian U, Archana Aravindan, Raymond P. Remigio, Gabriela Canalizo, Justin A. Kader, Marina Bianchin, Yiqing Song, Tianmu Gao, Jeff Rich, Rosalie McGurk. 2026-06-19. Clumpy Disk, Interloper, or Merger? Nature of a Distant Galaxy Pair at 5 kpc Projected Separation. https://arxiv.org/abs/2606.21007

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