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arXiv · 2402.16649

A Strongly Lensed Dusty Starburst of an Intrinsic Disk Morphology at Photometric Redshift of $z_{\rm ph}>7$

Chenxiaoji Ling·Bangzheng Sun·Cheng Cheng·Nan Li·Zhiyuan Ma·Haojing Yan
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Abstract

We present COSBO-7, a strong millimeter (mm) source known for more than sixteen years but was just revealed its near-to-mid-IR counterpart by the James Webb Space Telescope (JWST). The precise pin-pointing by the Atacama Large Millimeter Array (ALMA) on the exquisite NIRCam and MIRI images show that it is a background source gravitationally lensed by a single foreground galaxy, and the analysis of its spectral energy distribution by different tools is in favor of photometric redshift at $z_{\rm ph}>7$. Strikingly, our lens modeling based on the JWST data shows that it has a regular, disk morphology in the source plane. The dusty region giving rise to the far-IR-to-mm emission seems to be confined to a limited region to one side of the disk and has a high dust temperature of $>90$~K. The galaxy is experiencing starburst both within and outside of this dusty region. After taking the lensing magnification of $μ\approx 2.5-3.6$ into account, the intrinsic star formation rate is several hundred $M_\odot$~yr$^{-1}$ both within the dusty region and across the more extended stellar disk, and the latter already has $>10^{10}M_\odot$ of stars in place. If it is indeed at $z>7$, COSBO-7 presents an extraordinary case that is against the common wisdom about galaxy formation in the early universe; simply put, its existence poses a critical question to be answered: how could a massive disk galaxy come into being so early in the universe and sustain its regular morphology in the middle of an enormous starburst?

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Chenxiaoji Ling, Bangzheng Sun, Cheng Cheng, Nan Li, Zhiyuan Ma, Haojing Yan. 2024-07-04. A Strongly Lensed Dusty Starburst of an Intrinsic Disk Morphology at Photometric Redshift of $z_{\rm ph}>7$. https://arxiv.org/abs/2402.16649

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