MIRI spectrophotometry of GN-z11: Detection and nature of an optical red continuum component

A. Crespo Gómez; L. Colina; P. G. Pérez-González; J. Álvarez-Márquez; M. García-Marín; A. Alonso-Herrero; M. Annunziatella; A. Bik; S. Bosman; A. J. Bunker; A. Labiano; D. Langeroodi; P. Rinaldi; G. Östlin; L. Boogaard; S. Gillman; G. Barro; S. L. Finkelstein; G. C. K. Leung

doi:10.1051/0004-6361/202556814

paper

MIRI spectrophotometry of GN-z11: Detection and nature of an optical red continuum component

arXiv:2512.02997 · doi:10.1051/0004-6361/202556814

Abstract

We present new MIRI F560W, F770W and F1000W imaging of GN-z11, extending the previous rest-frame coverage from 0.38 to 0.86 $μ$ m. We report significant detections (14 $σ$ ) in the F560W and F770W images, and a marginal detection (3.2 $σ$ ) in F1000W. Here, we analyse its SED combining new MIRI imaging data with archival NIRSpec/Prism and MRS spectroscopy, and NIRCam imaging. The continuum emission shows a flat energy distribution, in f $_{ν}$ , up to 0.5 $μ$ m, compatible with the presence of a mixed stellar population of young (4 $\pm$ 1 Myr) and mature (63 $\pm$ 23 Myr) stars that also account for the [O III], H $β$ and H $α$ emission lines. The continuum at rest-frame 0.66 $μ$ m shows a 36 $\pm$ 3% flux excess above the predicted flux for a mixed stellar population, pointing to the presence of an additional source contributing at these wavelengths. This excess increases to 91 $\pm$ 28% at rest-frame 0.86 $μ$ m, although with a large uncertainty due to the marginal detection in the F1000W filter. We consider that hot dust emission in the dusty torus around a type 2 AGN could be responsible for the observed excess. Alternatively, this excess could be due to hot dust emission or to a photoluminiscence dust process (Extended Red Emission, ERE) under the extreme UV radiation field, as observed in some local metal-poor galaxies and in young compact starbursts. The presence of a type 1 AGN is not supported by the observed SED since high-z QSOs contribute at wavelengths above rest-frame 1 $μ$ m, and an additional ad-hoc red source would be required to explain the observed flux excess at 0.66 and 0.86 $μ$ m. Additional deep MIRI imaging covering the rest-frame near-IR are needed to confirm the flux detection at 10 $μ$ m with higher significance, and to discriminate between the different hot dust emission in the extreme starburst and AGN scenarios with MIRI imaging at longer wavelengths.

arXiv comment14 pages, 5 figures

MIRI spectrophotometry of GN-z11: Detection and nature of an optical red continuum component

Abstract

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