An almost NIRCam-dark dusty star-forming galaxy at z=6.63
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arXiv
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| Natura: | Preprint |
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2025
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| author | Bing, Longji Oliver, Seb Xiao, Mengyuan Lagache, Guilaine Adscheid, Sylvia Liu, Daizhong Magnelli, Benjamin Neri, Roberto Dessauges-Zavadsky, Miroslava Koekemoer, Anton M. Franco, Maximilien Jin, Shuowen Cooper, Olivia R. Faisst, Andreas L. Casey, Catilin M. Kartaltepe, Jeyhan S. Akins, Hollis Beelen, Alexandre Elbaz, David Gillman, Steven Harish, Santosh Long, Arianna S. McCracken, Henry Joy Oesch, Pascal Paquereau, Louise Ponthieu, Nicolas Rhodes, Jason Robertson, Brant Sanders, David B. Shuntov, Marko Wilkins, Stephen |
| author_facet | Bing, Longji Oliver, Seb Xiao, Mengyuan Lagache, Guilaine Adscheid, Sylvia Liu, Daizhong Magnelli, Benjamin Neri, Roberto Dessauges-Zavadsky, Miroslava Koekemoer, Anton M. Franco, Maximilien Jin, Shuowen Cooper, Olivia R. Faisst, Andreas L. Casey, Catilin M. Kartaltepe, Jeyhan S. Akins, Hollis Beelen, Alexandre Elbaz, David Gillman, Steven Harish, Santosh Long, Arianna S. McCracken, Henry Joy Oesch, Pascal Paquereau, Louise Ponthieu, Nicolas Rhodes, Jason Robertson, Brant Sanders, David B. Shuntov, Marko Wilkins, Stephen |
| contents | We present AC-2168, an almost NIRCam-dark, millimetre-bright galaxy in the COSMOS field. The source was identified blindly in ALMA Band-4 continuum data and remains undetected in the COSMOS-Web DR1 NIRCam catalogue. We spectroscopically confirm a redshift of $z_{\rm spec}=6.631$ from [CII] 158 $μ$m and four tentatively detected CO lines in NOEMA and ALMA data. SED fitting to near-IR to millimetre photometry yields $\rm L_{IR}=1.6\times10^{12}\,L_\odot$, an SFR of $\rm 244\,M_\odot/yr$, heavy dust attenuation $\rm A_V=5.4$ mag, and a stellar mass $\rm M_\star=3.7\times10^{10}\,M_\odot$. From the millimetre continuum and [CII] emission, we infer a warm ISM with $\rm T_{\rm dust}=60K$, $\rm M_{dust}=3.0\times10^{8}\,M_\odot$ and $\rm M_{gas}=4.1\times10^{10}\,M_\odot$. AC-2168 has a gas fraction ($f_{\rm gas}=M_{\rm gas}/(M_\star+M_{\rm gas})$) of $\sim52\%$, a short depletion time of $\rm \sim170Myr$, a compact ($\rm \sim1kpc$) dust-continuum size, and an SFR consistent with the star-forming main sequence at its mass. These properties match expectations for progenitors of massive quiescent galaxies at the peak of their assembly, as implied by NIRSpec-based SFHs of $z\sim4-5$ systems. Using the blind detection, we estimate a space density of $\rm 7.8^{+18.0}_{-6.5}\times10^{-6}\,cMpc^{-3}$ for AC-2168-like NIRCam-dark galaxies at $z\sim6-7$, $\sim42\%$ of the abundance of massive quiescent galaxies at $z\sim4-5$. No overdensity of Ly$α$ emitters or Lyman-break galaxies is found nearby, suggesting AC-2168 does not lie in a prominent protocluster and highlighting the importance of unbiased blind surveys for this population. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_08672 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | An almost NIRCam-dark dusty star-forming galaxy at z=6.63 Bing, Longji Oliver, Seb Xiao, Mengyuan Lagache, Guilaine Adscheid, Sylvia Liu, Daizhong Magnelli, Benjamin Neri, Roberto Dessauges-Zavadsky, Miroslava Koekemoer, Anton M. Franco, Maximilien Jin, Shuowen Cooper, Olivia R. Faisst, Andreas L. Casey, Catilin M. Kartaltepe, Jeyhan S. Akins, Hollis Beelen, Alexandre Elbaz, David Gillman, Steven Harish, Santosh Long, Arianna S. McCracken, Henry Joy Oesch, Pascal Paquereau, Louise Ponthieu, Nicolas Rhodes, Jason Robertson, Brant Sanders, David B. Shuntov, Marko Wilkins, Stephen Astrophysics of Galaxies We present AC-2168, an almost NIRCam-dark, millimetre-bright galaxy in the COSMOS field. The source was identified blindly in ALMA Band-4 continuum data and remains undetected in the COSMOS-Web DR1 NIRCam catalogue. We spectroscopically confirm a redshift of $z_{\rm spec}=6.631$ from [CII] 158 $μ$m and four tentatively detected CO lines in NOEMA and ALMA data. SED fitting to near-IR to millimetre photometry yields $\rm L_{IR}=1.6\times10^{12}\,L_\odot$, an SFR of $\rm 244\,M_\odot/yr$, heavy dust attenuation $\rm A_V=5.4$ mag, and a stellar mass $\rm M_\star=3.7\times10^{10}\,M_\odot$. From the millimetre continuum and [CII] emission, we infer a warm ISM with $\rm T_{\rm dust}=60K$, $\rm M_{dust}=3.0\times10^{8}\,M_\odot$ and $\rm M_{gas}=4.1\times10^{10}\,M_\odot$. AC-2168 has a gas fraction ($f_{\rm gas}=M_{\rm gas}/(M_\star+M_{\rm gas})$) of $\sim52\%$, a short depletion time of $\rm \sim170Myr$, a compact ($\rm \sim1kpc$) dust-continuum size, and an SFR consistent with the star-forming main sequence at its mass. These properties match expectations for progenitors of massive quiescent galaxies at the peak of their assembly, as implied by NIRSpec-based SFHs of $z\sim4-5$ systems. Using the blind detection, we estimate a space density of $\rm 7.8^{+18.0}_{-6.5}\times10^{-6}\,cMpc^{-3}$ for AC-2168-like NIRCam-dark galaxies at $z\sim6-7$, $\sim42\%$ of the abundance of massive quiescent galaxies at $z\sim4-5$. No overdensity of Ly$α$ emitters or Lyman-break galaxies is found nearby, suggesting AC-2168 does not lie in a prominent protocluster and highlighting the importance of unbiased blind surveys for this population. |
| title | An almost NIRCam-dark dusty star-forming galaxy at z=6.63 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2511.08672 |