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The JWST discovery of ``little red dots'' (LRDs) is reshaping our picture of the early Universe, yet the physical mechanisms driving their compact size and UV-optical colors remain elusive. Here we report an unusually bright LRD (z=3. 1) observed as part of the RUBIES program. This LRD exhibits broad emission lines (FWHM 4000km/s), a blue UV continuum, a clear Balmer break and a red continuum sampled out to rest 4 m with MIRI. We develop a new joint galaxy and AGN model within the Prospector Bayesian inference framework and perform spectrophotometric modeling using NIRCam, MIRI, and NIRSpec/Prism observations. Our fiducial model reveals a M_* 10⁹M_ galaxy alongside a dust-reddened AGN driving the optical emission. Explaining the rest-frame optical color as a reddened AGN requires A ₕ4, suggesting that a great majority of the accretion disk energy is re-radiated as dust emission. Yet despite clear AGN signatures, we find a surprising lack of hot torus emission, which implies that either the dust emission in this object must be cold, or the red continuum must instead be driven by a massive, evolved stellar population of the host galaxy -- seemingly inconsistent with the high EW broad lines (H EW 800). The widths and luminosities of Pa, Pa, Pa, and H imply a modest black hole mass of M ₁₇10⁸M_. Additionally, we identify a narrow blue-shifted HeI absorption in G395M spectra, signaling an ionized outflow with kinetic energy up to 1\% the luminosity of the AGN. The low redshift of RUBIES-BLAGN-1 combined with the depth and richness of the JWST imaging and spectroscopic observations provide a unique opportunity to build a physical model for these so-far mysterious LRDs, which may prove to be a crucial phase in the early formation of massive galaxies and their supermassive black holes.
Wang et al. (Mon,) studied this question.