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| Natura: | Preprint |
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2025
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| Accesso online: | https://arxiv.org/abs/2507.17738 |
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| author | Rinaldi, Pierluigi Rieke, George H. Wu, Zihao Gilbert, Carys J. E. Pacucci, Fabio Barchiesi, Luigi Alberts, Stacey Carniani, Stefano Bunker, Andrew J. Bhatawdekar, Rachana D'Eugenio, Francesco Ji, Zhiyuan Johnson, Benjamin D. Hainline, Kevin Kokorev, Vasily Kumari, Nimisha Iani, Edoardo Lyu, Jianwei Maiolino, Roberto Parlanti, Eleonora Robertson, Brant E. Sun, Yang Vignali, Cristian Williams, Christina C. Willmer, Christopher N. A. Zhu, Yongda |
| author_facet | Rinaldi, Pierluigi Rieke, George H. Wu, Zihao Gilbert, Carys J. E. Pacucci, Fabio Barchiesi, Luigi Alberts, Stacey Carniani, Stefano Bunker, Andrew J. Bhatawdekar, Rachana D'Eugenio, Francesco Ji, Zhiyuan Johnson, Benjamin D. Hainline, Kevin Kokorev, Vasily Kumari, Nimisha Iani, Edoardo Lyu, Jianwei Maiolino, Roberto Parlanti, Eleonora Robertson, Brant E. Sun, Yang Vignali, Cristian Williams, Christina C. Willmer, Christopher N. A. Zhu, Yongda |
| contents | Little Red Dots (LRDs) are compact, red sources discovered by JWST at high redshift ($z \gtrsim 4$), marked by distinctive "V-shaped" spectral energy distributions (SEDs) and often interpreted as rapidly accreting AGNs. Their evolution remains unclear, as identifying counterparts at lower redshifts is challenging. We present WISEA J123635.56+621424.2 (here dubbed {\it the Saguaro}), a $z=2.0145$ galaxy in GOODS-North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower-redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connection to LRDs includes that: (1) its nuclear spectrum shows a clear "V-shaped" SED; and (2) when redshifted to $z=7$, surface brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface brightness dimming alone can explain their compact appearance. Lastly, we show that {\it the Saguaro} is not unique by describing similar objects from the literature at $z\lesssim3.5$. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could be the visible nuclei of galaxies undergoing a short-lived, AGN-dominated evolutionary phase, with their compact, red appearance driven largely by observational biases. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_17738 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs Rinaldi, Pierluigi Rieke, George H. Wu, Zihao Gilbert, Carys J. E. Pacucci, Fabio Barchiesi, Luigi Alberts, Stacey Carniani, Stefano Bunker, Andrew J. Bhatawdekar, Rachana D'Eugenio, Francesco Ji, Zhiyuan Johnson, Benjamin D. Hainline, Kevin Kokorev, Vasily Kumari, Nimisha Iani, Edoardo Lyu, Jianwei Maiolino, Roberto Parlanti, Eleonora Robertson, Brant E. Sun, Yang Vignali, Cristian Williams, Christina C. Willmer, Christopher N. A. Zhu, Yongda Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics Little Red Dots (LRDs) are compact, red sources discovered by JWST at high redshift ($z \gtrsim 4$), marked by distinctive "V-shaped" spectral energy distributions (SEDs) and often interpreted as rapidly accreting AGNs. Their evolution remains unclear, as identifying counterparts at lower redshifts is challenging. We present WISEA J123635.56+621424.2 (here dubbed {\it the Saguaro}), a $z=2.0145$ galaxy in GOODS-North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower-redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connection to LRDs includes that: (1) its nuclear spectrum shows a clear "V-shaped" SED; and (2) when redshifted to $z=7$, surface brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface brightness dimming alone can explain their compact appearance. Lastly, we show that {\it the Saguaro} is not unique by describing similar objects from the literature at $z\lesssim3.5$. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could be the visible nuclei of galaxies undergoing a short-lived, AGN-dominated evolutionary phase, with their compact, red appearance driven largely by observational biases. |
| title | Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2507.17738 |