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arXiv · 2605.29149

Compact near infrared sources in the center of the extraordinary galaxy IC 860

J. S. Gallagher·L. Schisgal·G. C. Privon·S. Aalto·S. König·R. Kotulla·J. Mangum·W. St. John·D. Rigopoulou·K. Alatalo
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Abstract

Hubble Space Telescope (HST) images are used to study the structure of the central regions of the luminous infrared galaxy (LIRG) IC 860. IC 860 is of special interest as a system due to its extreme central concentration of molecular gas cloaking its compact obscured nucleus (CON). The CON provides most of the 1.5E11 Lsun luminosity in IC 860 from an undetermined combination of stellar and AGN power sources. We mapped and photometered the central molecular zone (CMZ) of IC 860 motivated by a previous NIR detection of a luminous compact nuclear source. Our objective was to study properties of the CMZ and its relationship to the CON, that we identified as an opaque central region in archival near infrared (NIR) images. Coordinates of the compact NIR source, IC860-a, came from HST image coordinates calibrated with Gaia positions. Photometry of the HST images yielded magnitudes, colors, and high V-band dust optical depths based on foreground screen dust models. Photometry corrected for dimming by dust yielded NIR luminosities of IC860-a and the CMZ. We found IC 860 has distinct compact central luminosity sources: Most of the NIR luminosity is from the CMZ while the LIRG-CON is an obscured region centered in the CMZ. IC860-a, in the northeast side of the CMZ, is offset by about 0.2 arcsec from the CON, has a luminosity of approximately 1E9 Lsun, and may be a massive young stellar complex or intruding nucleus. We concluded that the inner CMZ in IC 860 contains two luminous compact objects: The CON is identified for the first time as an obscured central source while the structure of the CMZ and CON is complicated by the presence of the IC860-a compact object, possibly a massive young stellar system or second nucleus. The presence of IC 860-a in combination with the CON is a further signature of the unusual evolution of the gas-rich IC 860 CMZ.

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J. S. Gallagher, L. Schisgal, G. C. Privon, S. Aalto, S. König, R. Kotulla, J. Mangum, W. St. John, D. Rigopoulou, K. Alatalo. 2026-05-27. Compact near infrared sources in the center of the extraordinary galaxy IC 860. https://arxiv.org/abs/2605.29149

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