A dust-reddened quasar in a [C II]-luminous host at z=6.55

Abstract

Most known quasars at z>6 were selected through their rest-frame UV emission. Only a small number of reddened quasars have been identified at these redshifts, leaving their nuclear and host-galaxy properties poorly constrained. We present JWST/NIRSpec spectroscopy and ALMA band 6 observations of the quasar J1440+0019 at z=6.5488, revealing its dust-reddened nature and jointly characterizing its nucleus and host galaxy. The continuum is best described by an SMC-like extinction law with E(B−V)=0.20±0.03. Three absorption systems detected in N V, Si IV, and C IV are blueshifted by approximately $900−−3600$ km s⁻¹ and likely trace an ionized nuclear outflow. The broad Mg II line and extinction-corrected continuum yield a black-hole mass of log(M_BH/M_⊙)=9.04±0.42, a bolometric luminosity of L_bol≃1.1×10⁴⁷ erg s⁻¹, and an Eddington ratio of λ_Edd≃0.8. ALMA observations further reveal its host galaxy to be among the most [C II]-luminous known at z>6, with L_{[C II]}=(7.21±0.25)×10⁹ L_⊙. For a fiducial dust temperature of 47 K and emissivity index β=1.6, the dust continuum implies L_TIR=8.9×10¹² L_⊙ and M_dust=4.0×10⁸ M_⊙. The inferred dynamical mass places J1440+0019 in the region of the M_BH--M_dyn plane occupied by high-redshift blue quasars. These observations reveal a moderately reddened, rapidly accreting quasar in a luminous, dust-rich host during reionization. Its measured nuclear and host-galaxy properties provide an observational reference for identifying and characterizing similar systems in future systematic searches with wide-area infrared surveys.

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BibTeX RIS

BibTeX

@misc{yang2026dustreddened,
  title = {{A dust-reddened quasar in a [C II]-luminous host at z=6.55}},
  author = {Daming Yang and Joseph F. Hennawi and Rychard Bouwens and Timo Kist and Eduardo Bañados and Hiddo S. B. Algera and Aaron J. Barth and Sarah E. I. Bosman and Frederick B. Davies and Anna-Christina Eilers and Xiaohui Fan and Victoria A. Fawcett and Yuming Fu and Anniek J. Gloudemans and Francesco Guarneri and Bin Jia and Elia Pizzati and Huub Röttgering and Jan-Torge Schindler and Feige Wang and Jinyi Yang},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.13758},
  eprint = {2610.13758},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.13758},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - A dust-reddened quasar in a [C II]-luminous host at z=6.55
AU  - Daming Yang
AU  - Joseph F. Hennawi
AU  - Rychard Bouwens
AU  - Timo Kist
AU  - Eduardo Bañados
AU  - Hiddo S. B. Algera
AU  - Aaron J. Barth
AU  - Sarah E. I. Bosman
AU  - Frederick B. Davies
AU  - Anna-Christina Eilers
AU  - Xiaohui Fan
AU  - Victoria A. Fawcett
AU  - Yuming Fu
AU  - Anniek J. Gloudemans
AU  - Francesco Guarneri
AU  - Bin Jia
AU  - Elia Pizzati
AU  - Huub Röttgering
AU  - Jan-Torge Schindler
AU  - Feige Wang
AU  - Jinyi Yang
PY  - 2026
DA  - 2026/10/09
PB  - arXiv
DO  - 10.48550/arxiv.2610.13758
UR  - https://arxiv.org/abs/2610.13758
AB  - Most known quasars at z>6 were selected through their rest-frame UV emission. Only a small number of reddened quasars have been identified at these redshifts, leaving their nuclear and host-galaxy properties poorly constrained. We present JWST/NIRSpec spectroscopy and ALMA band 6 observations of the quasar J1440+0019 at z=6.5488, revealing its dust-reddened nature and jointly characterizing its nucleus and host galaxy. The continuum is best described by an SMC-like extinction law with E(B−V)=0.20±0.03. Three absorption systems detected in N V, Si IV, and C IV are blueshifted by approximately $900−−3600$ km s^−1 and likely trace an ionized nuclear outflow. The broad Mg II line and extinction-corrected continuum yield a black-hole mass of log(M_BH/M_⊙)=9.04±0.42, a bolometric luminosity of L_bol≃1.1×10^47 erg s^−1, and an Eddington ratio of λ_Edd≃0.8. ALMA observations further reveal its host galaxy to be among the most [C II]-luminous known at z>6, with L_[C II]=(7.21±0.25)×10^9 L_⊙. For a fiducial dust temperature of 47 K and emissivity index β=1.6, the dust continuum implies L_TIR=8.9×10^12 L_⊙ and M_dust=4.0×10^8 M_⊙. The inferred dynamical mass places J1440+0019 in the region of the M_BH--M_dyn plane occupied by high-redshift blue quasars. These observations reveal a moderately reddened, rapidly accreting quasar in a luminous, dust-rich host during reionization. Its measured nuclear and host-galaxy properties provide an observational reference for identifying and characterizing similar systems in future systematic searches with wide-area infrared surveys.
ER  -

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