Compact Core, Extended Reach: A Bipolar kpc-Scale Elongation in a Little Red Dot at z ≈ 5.5
Abstract
Little Red Dots (LRDs) appear extremely compact at rest-frame optical wavelengths, yet many show extended rest-frame UV morphology revealing more complex internal structure. We present a combined analysis of VLT/MUSE rest-frame UV integral-field spectroscopy and continuum-subtracted [O III], Hβ, and Hα+[N II] emission-line maps from JWST/NIRCam imaging at sub-kpc resolution for LRD-204851 at z=5.482 in GOODS-S. We find that LRD-204851 hosts a remarkably thin, bipolar, elongated structure passing through the optical continuum centroid and extending several kpc on either side, traced by both the UV continuum and the rest-frame optical emission lines, with a bright [O III] clump-like structure ∼2 kpc to the south-east of the centroid. The MUSE observations reveal a double-peaked Lyα profile, with a broad and bright near-systemic red peak and a relatively faint peak blueshifted by ∼430 km s−1, accompanied by a tentative N V λ1238 detection at similar velocity. In narrow-band imaging extracted from the MUSE IFU cube, both the blue Lyα peak and the tentative N V emission lean toward this same south-eastern direction. Independently, radiative-transfer modeling of the integrated Lyα profile favors a biconical low-column-density cavity in a dense, slowly expanding neutral envelope, in support of the bipolar geometry traced by the line maps. Together, these results suggest that the elongated emission of LRD-204851 is connected to radiation and/or gas flow from its central engine through a low-column-density channel with a small opening angle that may trace either a slow outflow or a quasi-static ionization cone. LRD-204851 is one of the first LRDs where the central engine's impact on its host galaxy is potentially directly observable on kpc scales.
Versions
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BibTeX
@misc{ji2026compact,
title = {{Compact Core, Extended Reach: A Bipolar kpc-Scale Elongation in a Little Red Dot at $z \approx 5.5$}},
author = {Zhiyuan Ji and Yang Sun and Mauro Giavalisco and Yongda Zhu and George H. Rieke and Christina C. Williams and Michael V. Maseda and Jianwei Lyu and Marcia Rieke and Sandro Tacchella},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2606.18342},
eprint = {2606.18342},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.18342},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Compact Core, Extended Reach: A Bipolar kpc-Scale Elongation in a Little Red Dot at z ≈ 5.5
AU - Zhiyuan Ji
AU - Yang Sun
AU - Mauro Giavalisco
AU - Yongda Zhu
AU - George H. Rieke
AU - Christina C. Williams
AU - Michael V. Maseda
AU - Jianwei Lyu
AU - Marcia Rieke
AU - Sandro Tacchella
PY - 2026
DA - 2026/08/28
PB - arXiv
DO - 10.48550/arxiv.2606.18342
UR - https://arxiv.org/abs/2606.18342
AB - Little Red Dots (LRDs) appear extremely compact at rest-frame optical wavelengths, yet many show extended rest-frame UV morphology revealing more complex internal structure. We present a combined analysis of VLT/MUSE rest-frame UV integral-field spectroscopy and continuum-subtracted [O III], Hβ, and Hα+[N II] emission-line maps from JWST/NIRCam imaging at sub-kpc resolution for LRD-204851 at z=5.482 in GOODS-S. We find that LRD-204851 hosts a remarkably thin, bipolar, elongated structure passing through the optical continuum centroid and extending several kpc on either side, traced by both the UV continuum and the rest-frame optical emission lines, with a bright [O III] clump-like structure ∼2 kpc to the south-east of the centroid. The MUSE observations reveal a double-peaked Lyα profile, with a broad and bright near-systemic red peak and a relatively faint peak blueshifted by ∼430 km s^−1, accompanied by a tentative N V λ1238 detection at similar velocity. In narrow-band imaging extracted from the MUSE IFU cube, both the blue Lyα peak and the tentative N V emission lean toward this same south-eastern direction. Independently, radiative-transfer modeling of the integrated Lyα profile favors a biconical low-column-density cavity in a dense, slowly expanding neutral envelope, in support of the bipolar geometry traced by the line maps. Together, these results suggest that the elongated emission of LRD-204851 is connected to radiation and/or gas flow from its central engine through a low-column-density channel with a small opening angle that may trace either a slow outflow or a quasi-static ionization cone. LRD-204851 is one of the first LRDs where the central engine's impact on its host galaxy is potentially directly observable on kpc scales.
ER -