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

abstract · 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 $E(B-V)=0.20\pm0.03$. 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 $\log(M_{\rm BH}/M_\odot)=9.04\pm0.42$, a bolometric luminosity of $L_{\rm bol}\simeq1.1\times10^{47}$ erg s$^{-1}$, and an Eddington ratio of $λ_{\rm Edd}\simeq0.8$. ALMA observations further reveal its host galaxy to be among the most [C II]-luminous known at $z>6$, with $L_{\mathrm{[C II]}}=(7.21\pm0.25)\times10^9 L_\odot$. For a fiducial dust temperature of 47 K and emissivity index $β=1.6$, the dust continuum implies $L_{\rm TIR}=8.9\times10^{12} L_\odot$ and $M_{\rm dust}=4.0\times10^8 M_\odot$. The inferred dynamical mass places J1440+0019 in the region of the $M_{\rm BH}$--$M_{\rm dyn}$ 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.

S5: 5 Conclusions / block 1 · html

We have combined JWST/NIRSpec spectroscopy and ALMA observations to characterize the nucleus and host of the reddened quasar J1440 + + 0019 at z = 6.5488 z=6.5488 . Our main results are:

S5: 5 Conclusions / block 1 · html

The continuum is best described by SMC-like extinction with E ⁡ ( B − V ) = 0.195 ± 0.03 E(B-V)=0.195\pm 0.03 , where the uncertainty reflects the unknown intrinsic continuum slope. The spectrum shows no evidence for a 2175 Å extinction feature.

S5: 5 Conclusions / block 1 · html

Three high-ionization absorption systems exhibit blueshifts reaching approximately 3600 ​ km ​ s − 1 3600\penalty\ \mathrm{km\,s^{-1}} . Their N v , Si iv , and C iv absorption supports an intrinsic or associated origin, although the location and dust content of the absorbing gas remain unconstrained.

S5: 5 Conclusions / block 1 · html

The extinction-corrected Mg ii fit gives log ⁡ ( M BH / M ⊙ ) = 9.04 ± 0.42 \log(M_{\rm BH}/M_{\odot})=9.04\pm 0.42 . Applying a bolometric correction of BC 3000 = 5.15 {\rm BC}_{3000}=5.15 to the dereddened continuum luminosity at 3000 Å gives L bol = 1.1 × 10 47 ​ erg ​ s − 1 L_{\rm bol}=1.1\times 10^{47}\penalty\ {\rm erg\,s^{-1}} , corresponding to an Eddington ratio of λ Edd ≃ 0.8 \lambda_{\rm Edd}\simeq 0.8 .

S5: 5 Conclusions / block 1 · html

The host has L [ C ​ ii ] = 7.21 × 10 9 ​ L ⊙ L_{\rm[{C\textsc{ii}}]}=7.21\times 10^{9}\penalty\ L_{\odot} . For T dust = 47 T_{\rm dust}=47 K and β = 1.6 \beta=1.6 , its continuum implies L TIR = 8.9 × 10 12 ​ L ⊙ L_{\rm TIR}=8.9\times 10^{12}\penalty\ L_{\odot} , M dust ≃ 4.0 × 10 8 ​ M ⊙ M_{\rm dust}\simeq 4.0\times 10^{8}\penalty\ M_{\odot} , and an upper limit of approximately 1330 ​ M ⊙ ​ yr − 1 1330\penalty\ M_{\odot}\,{\rm yr^{-1}} on the SFR. The [C ii ] emission is marginally resolved in space, with disk and dispersion-dominated prescriptions giving M dyn ≃ 2.9 × 10 10 M_{\rm dyn}\simeq 2.9\times 10^{10} and 1.1 × 10 11 ​ M ⊙ 1.1\times 10^{11}\penalty\ M_{\odot} , respectively. No broad [C ii ] component is detected within the observed velocity range, which does not cover the UV absorption systems.

S5: 5 Conclusions / block 1 · html

The Eddington ratio and position of J1440 + + 0019 in the M BH M_{\rm BH} – M dyn M_{\rm dyn} plane are similar to those of high-redshift blue quasars. Its host lies at the luminous end of their distribution, with a relatively high L [ C ​ ii ] / L TIR = 8.1 × 10 − 4 L_{\rm[{C\textsc{ii}}]}/L_{\rm TIR}=8.1\times 10^{-4} at comparable L TIR L_{\rm TIR} . The dispersion-dominated mass estimate remains consistent with the intrinsic scatter of the local black-hole–bulge relation.

S5: 5 Conclusions / block 1 · html

The nuclear reddening of J1440 + + 0019 resembles that of moderately reddened low-redshift quasars, while its dust reservoir is comparable to those of more heavily reddened systems. Its nominal Eddington ratio exceeds those of most objects in the low-redshift comparison samples. The radio limits are too shallow to test the compact radio excess reported for low-redshift red quasars.

S5: 5 Conclusions / block 1 · html

Among reddened and obscured sources at z > 6 z>6 , J1440 + + 0019 resembles J1205 − - 0000 in its nuclear spectrum but has a more luminous host, comparable to COS-87259. GNz7q instead has a smaller black hole and a higher nominal Eddington ratio, while the obscured SHELLQs quasars have much weaker UV continua relative to their emission lines. These comparisons show that red and obscured sources span diverse accretion states and host properties.

A2: Appendix B Comparison of extinction laws / block 1 · html

Figure 9 compares the resulting fits. The SMC curve gives the lowest reduced χ 2 \chi^{2} , with χ 2 / ν = 3.6 \chi^{2}/\nu=3.6 , where ν \nu is the number of fitted pixels minus two. The LMC average, LMC2, and Milky Way curves give χ 2 / ν = 64.7 \chi^{2}/\nu=64.7 , 25.4, and 93.0, respectively. Their main discrepancy is the broad depression associated with the 2175 Å extinction feature, which falls at an observed wavelength of 1.64 ​ μ ​ m 1.64\penalty\ \mu{\rm m} at the systemic redshift of J1440 + + 0019. The observed continuum shows no corresponding trough, including at the weaker depth predicted by the LMC2 curve.

PDF page 15 / block 2 · pdf

inally, we estimated the black hole mass (MBH) from the width and luminosity of the Hα BLR compo- nent, following the recipe of Greene & Ho (2005) and Reines et al. (2013). The resultant values (MBH = 107.8−9.1M⊙) overlap with the distributions of low- z SDSS quasars (e.g., Rakshit et al. 2020; Toba et al. 2021) and UV-luminous quasars at z ∼ 6 (e.g., Yang et al. 2021), but are at the lower end on av- erage. The Eddington ratios are in the range from λEdd = 0.5 to 1.1, suggesting that sub-Eddington to Ed- dington accretion takes place in the BL objects. Figure Figure 8. Black hole masses and bolometric lumi- nosities of luminous quasars (open squares; Willott et al. 2010; Shen et al. 2019; Yang et al. 2021, 2023) and SHEL- LQs low-luminosity quasars (grey dots; Onoue et al. 2019; Matsuoka et al. 2019b; Onoue et al. 2024, M. Onoue et al., in prep.) at z ∼ 6 −7. The dark blue sym- bols represent JWST BHEs at z > 4 (Harikane et al. 2023; ¨Ubler et al. 2023; Furtak et al. 2024; Greene et al. 2024; Juodˇzbalis et al. 2024, 2025; Maiolino et al. 2024b; Matthee et al. 2024; Schindler et al. 2024; Lin et al. 2025). The dotted lines represent constant Eddington ratios of λEdd = 1, 0.1, and 0.01, from top to bottom. 8 compares the estimated values with those of classical quasars and other JWST BHEs,4 demonstrating that the present objects bridge the two AGN populations. We also note the overall similarity of the present tar- gets with the SDSS type-II quasar candidates at lower redshifts (Alexandroffet al. 2013; Greene et al. 2014), both of which are characterized by black hole masses of MBH ∼108−9M⊙with sub-Eddington accretion, mild dust obscuration (AV ∼0 −3 mag), and high line lumi- nosities (L[OIII] ∼1043−45 erg s−1). However, we caution that our estimates reported above have large uncertainties. Black hole masses derived from single-epoch spectra are associated with statistical uncertainty of 0.3 – 0.5 dex (e.g., Vestergaard & Peterson 2006). The bolometric correc- tion to Hα luminosity has been derived from low-z AGNs, and we do not know how accurate it is when 4 This figure is a collection of heterogeneous measurements, since different works used different assumptions

PDF page 20 / block 3 · pdf

nding the whole picture of SMBH activity during cosmic dawn. 4. SUMMARY We present the results from JWST/NIRSpec observa- tions of 13 objects in the EoR. The sample was originally selected by the HSC-SSP imaging survey over >1000 deg2, and all the objects have luminous Lyα emission

S5: 5 Conclusions / block 1 · html

Massive cold gas reservoirs and contrasting obscured star formation. ALMA reveals luminous [C ii ] 158 ​ μ 158\,\mu m emission in both sources ( L [ CII ] ≃ 0.8 L_{\rm[CII]}\simeq 0.8 and 4.1 × 10 9 ​ L ⊙ 4.1\times 10^{9}\,L_{\odot} for J1450 − - 0144 and J1429 − - 0104, respectively) and a clear dust-continuum detection in J1429 − - 0104 ( L TIR ≃ 2.6 × 10 12 ​ L ⊙ L_{\rm TIR}\simeq 2.6\times 10^{12}\,L_{\odot} , SFR IR ≃ 310 ​ M ⊙ ​ yr − 1 \mathrm{SFR_{IR}}\simeq 310\,M_{\odot}\,{\rm yr}^{-1} ), while J1450 − - 0144 remains undetected in the continuum. Both galaxies are ≳ 1 \gtrsim 1 mag brighter in the rest-frame UV than typical REBELS galaxies yet match the most [C ii ]-luminous REBELS sources, and the implied molecular gas masses of M mol ∼ 10 10 M_{\rm mol}\sim 10^{10} – 10 11 ​ M ⊙ 10^{11}\,M_{\odot} correspond to depletion times of a few hundred Myr, sufficient to sustain the present star-formation episodes provided the gas reservoirs are not disrupted. The two galaxies nonetheless differ sharply in obscuration: J1429 − - 0104 sits in the ultra-luminous infrared regime with an obscured-to-total star-formation fraction of ≈ 70 \approx 70 per cent and lies well above the Calzetti-like and SMC-like IRX– β \beta relations, whereas the 2 ​ σ 2\sigma IRX upper limit of J1450 − - 0144 is consistent with little obscured star formation. A potential explanation for the IRX excess of J1429 − - 0104 is that its UV and FIR emission arise from spatially distinct regions, consistent with the ∼ 1 ′′ \sim 1^{\prime\prime} ( ∼ 5.4 \sim 5.4 kpc) offset between its rest-UV centroid and the [C ii ]/dust peak, whose origin (a merger, an obscured central starburst, or feedback-driven dust displacement) require future high-resolution imaging (Sect. 3.3 and 4.1 ).

S2.SS1: 2.1 Initial discovery / block 1 · html

A summary of the basic properties of J1429 − - 0104 and J1450 − - 0144 is presented in Table 1 . Note that we have updated the redshifts using the [C ii ] line from our ALMA observations (Sect. 3.3 ) and M 1450 M_{1450} from our JWST/NIRSpec data (Sect. 2.2.2 ). In Fig. 1 we show the two galaxies in the redshift versus M UV M_{\rm UV} plane with these updated values.

S3.SS1: III.1 Spectral fitting / block 1 · html

This procedure results in a good fit for one of the objects, CFHQS J2229+1457, which exhibits pronounced narrow emission lines, while we need to implement further constraints to fit the rest of the spectra due to their relatively weak [O III ] lines that blend with the enhanced [Fe II ] emission. In particular, for all other quasars we model the complex line profiles of H α \alpha and H β \beta with two broad Gaussian components instead of one, and we also model the [S II ] λ ​ λ \lambda\lambda 6718 , 6732 \,6718,6732 doublet (with shared linewidths and velocity offsets but without a fixed line ratio) in order to accurately fit the red wing of the broadest H α \alpha component. We further tie the linewidths and velocity offsets of the narrow H α \alpha component to the single-Gaussian components of the [N II ] λ ​ λ \lambda\lambda 6549 , 6585 6549,6585 and [S II ] λ ​ λ \lambda\lambda 6718 , 6732 6718,6732 emission lines. Similarly, we tie the narrow component of H β \beta to the narrow components of [O III ] λ ​ λ \lambda\lambda 4959 , 5007 4959,5007 . The extracted quasar spectra as well as the resultant spectral fits are displayed in Fig. 1 .

S4.SS2: IV.2 Search for extended emission / block 1 · html

Table 4: A summary of H α \alpha and [O III ] nebular (non-)detections and their properties: the 5 ​ σ 5\sigma detection limit over a 1 ​ arcsec 2 1{\rm arcsec}^{2} aperture, SB 5 ​ σ 1 {\rm SB}^{1}_{5\sigma} , the maximum extent of the nebula, d max Neb d_{\rm max}^{\rm Neb} , and the corresponding lifetime measurement, log ⁡ t Q Neb \log{t_{\rm Q}^{\rm Neb}} .

S4: 4 Results / block 1 · html

X-ray images of each target were constructed by stacking the repeat exposures. The total exposure times are and 56.7 ks for G01, 56.5 ks for G02, 57.0 ks for G03, and 60.0 ks for G04, respectively. We examined those images in the 1-5 keV band, where the signal to noise ratio is expected to be optimal owing to low instrumental background. None of the targets were detected (Fig. 4 ). With the point spread function (PSF) of the ACIS-S, 60% of counts from a point source are expected to fall within a 1-pixel ( = 0.49 ​ ″ =0.49\arcsec ) radius (MARX document 5.2.2). No counts were observed within a 1-pixel radius from any of the four target positions. The background counts in the 1-5 keV band are 0.013-0.015 cts pixel -1 for these observations. Therefore no background count is expected (the probability of observing one or more background counts in the area is 4%), as observed. Detection of no counts sets the 95% upper limit to be 3 counts in each aperture, using a Bayesian formulation for a Poisson distribution of counts ( Kraft et al. 1991 ) . Assuming that each source has a photon-index Γ = 2 \Gamma=2 ( Huang et al. 2020 , e.g.) and absorbing column N H N_{\rm H} < 10 23 <10^{23} cm -2 , the corresponding rest-frame 2-10 keV luminosity at the median redshift of the four targets, z = 6.13 z=6.13 , is 2 × 10 44 2\times 10^{44} erg s -1 , which we adopt as the upper limit for each object for the discussion below.

S4: 4 Results / block 1 · html

We note that one count was registered at 0.8 arcsec (within a 2-pixel radius) from the target position in the G03 image. Given the PSF, the probability of detecting one source count in the second radial pixel but none in the first is 10%. Given the background level, observing one background count within the same area has a probability of 12%, assuming a Poisson process. Since the Bayes factor is around unity, no preference is given whether it is a source or background count. Even if it is a source count, the one count does not constitutes a detection, but gives an increased upper limit of 4.7 counts for G03, corresponding to 3 × 10 44 3\times 10^{44} erg s -1 .

Sx2: RESULTS / block 1 · html

Figure 3 : Multiphase clearing of the buried nucleus. The top panels show the Mg ii (left) and Na i D (right) absorption profiles. The lower panels show the Ly α \alpha velocity map (left) and velocity-dispersion map (right). Because the Ly α \alpha detection has a low signal-to-noise ratio (S/N), we use maps rebinned by 3 × 3 3\times 3 spatial pixels and show only pixels with S / N > 2 {\rm S/N}>2 . The gray circle shows the MUSE PSF with FWHM = = 0.66 ′′ . These absorption features trace cool outflowing gas, while the extended Ly α \alpha halo reveals kinematically complex gas on ∼ 20 \sim 20 kpc scales.

Sx17: Measuring host properties from image decomposition / block 1 · html

The source shows extended structure in the short-wavelength NIRCam bands. We therefore used JWST/NIRCam imaging to decompose the observed emission into a point source (i.e., the AGN) and an extended component (i.e., the host galaxy). The resulting host-galaxy photometry was then used to infer the stellar population properties, in particular the stellar mass.

S1: I Introduction / block 1 · html

In this paper, we present the first results on broad-line AGNs at z > 5 z>5 from COSMOS-3D. This first dataset, covering 127 arcmin 2 and representing just 10% of the full survey, already demonstrates the capabilities of COSMOS-3D in studying the nature of high-redshift AGNs. This work serves as a preview of the full potential of the survey. Detailed analyses of the complete COSMOS-3D sample will follow in future papers once the full dataset is available.

S1: I Introduction / block 1 · html

The paper is organized as follows. In § II , we introduce the datasets and methods to select broad-line AGNs. We present the analysis and results in § III , including the photometric and spectroscopic properties, variability, and luminosity function. We discuss the abundance of z > 7 z>7 AGNs in § IV . We adopt the AB magnitude system for all photometric measurements in this paper. Throughout this work, a flat Λ \Lambda CDM cosmology is assumed, with H 0 = 70 ​ km ​ s − 1 ​ Mpc − 1 \rm H_{0}=70~km~s^{-1}~Mpc^{-1} , Ω Λ , 0 = 0.7 \Omega_{\Lambda,0}=0.7 , and Ω m , 0 = 0.3 \Omega_{m,0}=0.3 .

abstract / block 1 · abstract

We analyze 23 spectroscopically confirmed Type-2 quasars (QSOs) selected from the WISE 22$\rm μ$m band in the SDSS Stripe 82 region, focusing on their multi-band photometry and spectral energy distributions (SEDs). These objects were selected to be IR-luminous ($\rm flux_{W4} > 5mJy$, i.e., $12.62 < W4 < 14.62 \rm\ AB \, magnitude$), optically faint ($r > 23$) or with red color ($r - W4 >8.38$). Gemini/GNIRS observations were conducted for all 24 candidates, and 18/24 were also observed with Keck/LRIS. The observations confirm 23 to be real Type-2 QSOs in the redshift range $0.88 - 2.99$ (12 are at $z>2$). We collect multi-band photometry and conduct SED fitting. The composite photometry probes the wavelength from 0.1$\rm μ$m to 10$\rm μ$m at the rest frame. The IR emission is dominated by dust torus implying an average torus luminosity for the sample of $L_{\rm torus} 10^{46.84} \rm erg/s$. The origin of the rest-UV/optical light is not definitive, but we present three possible scenarios: scattered light, stellar emission, and the reddened accretion disk. Assuming an obscured:unobscured ratio of approximately 1:1, our targets have $L_{\rm bol} = 10^{46.28} \rm erg \,s^{-1} - 10^{47.49} \rm erg \,s^{-1}$ and around SMBH masses $\rm 10^{8.18} M_{\odot} - 10^{9.39} M_{\odot}$, assuming they accreate at the Eddington limit. Compared to previous Type-2 AGN SEDs, our targets have a brighter dust torus and redder optical-IR color. By comparing the SED to the results from JWST `little red dots' (LRDs), we find that these IR-selected Type-2 QSOs have similar SED shapes to the LRDs. This pilot Type-2 QSO survey demonstrates that mid-IR selection is an efficient way to find luminous Type-2 QSOs at $z>2$. Finally, the composite photometry and Type-2 QSOs SED model generated by this sample provide a guide for finding more Type-2 QSOs at higher redshift.

S5: V Summary and Conclusions / block 1 · html

A morphological analysis on a subset of LoRDs with HSC coverage shows that the majority of sources ( > 80 % >80\% ) are compact regardless of their spectral shape (see Section IV.1 ). We find that LoRDs with a V-shaped continuum are more likely to have a resolved morphology compared to sources without the V-shape. This suggests that some of the V-shaped spectra ( ∼ 40 % \sim 40\% ) are the result of an underlying stellar population and thus are unlikely to serve as proper LRD analogs. The remaining ∼ 60 % \sim 60\% of V-shaped LoRDs are proper LRD analog candidates, but space-based imaging is necessary to quantify their compactness.

S5: V Summary and Conclusions / block 1 · html

In this paper we have shown that the JWST filters used to select LRDs at z ∼ 5 z\sim 5 align well with the SDSS filters at both z = 0.38 z=0.38 and z = 0.78 z=0.78 . We leverage this mapping to photometrically select Local Red Dots (LoRDs) from SDSS using selection criteria similar to the red1/red2 criteria from Greene et al. [45] ; our selection is given in Equations 2 and 3 . In total we find ∼ 1300 \sim 1300 QSOs which share similar photometric colors to the LRDs (Section II.1 ). While not every LoRD we identify serves as a proper analog to LRDs, this is the first step towards studying LRD-like systems in the local Universe at the population level where archival data is plentiful.