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Warm gas in the vicinity of a supermassive black hole 13 billion years ago

Nature Astronomy volume 9, pages 720–728 (2025)Cite this article

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Abstract

Quasars, powered by supermassive black holes, are among the brightest objects in the Universe. In the vicinity of a supermassive black hole, X-ray photons from an active galactic nucleus can heat the surrounding gas to several hundred kelvin. Here we report observations of dust continuum and carbon monoxide (CO) J = 13–12 and J = 14–13 line emissions at a resolution of 130 pc in a luminous quasar at a redshift of 6. We successfully detected these high-J CO line emissions from warm gas in a compact disk component. The CO luminosity ratio in the central region of the compact disk is consistent with theoretical models in which X-ray heating dominates the CO excitation and the gas column density is as high as 1025 cm−2. This finding demonstrates that high-resolution observations of high-J CO lines are promising ways to identify extremely dust-obscured quasars in the early Universe.

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Fig. 1: Morphology of a luminous quasar at z = 6.0, J2310+1855.
Fig. 2: A variation of luminosity ratio between CO J = 14–13 and CO J = 13–12 emissions at different galactocentric radii.
Fig. 3: Energy distributions of dust continuum and CO line emissions in J2310+1855.
Fig. 4: [CII] spectrum in J2310+1855.
Fig. 5: Schematic view of J2310+1855.
Fig. 6: Galaxy-integrated CO SLEDs.

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Data availability

All the ALMA data are publicly available via the ALMA archive at https://almascience.nao.ac.jp/aq/, with the programme IDs ADS/JAO.ALMA#2018.1.00597.S, ADS/JAO.ALMA#2019.1.00080.S, ADS/JAO.ALMA#2019.1.00661.S, ADS/JAO.ALMA#2019.1.01721.S and ADS/JAO.ALMA#2022.1.01473.S (see also Extended Data Table 1).

Code availability

The codes used in the data analysis (CASA, UVMULTIFIT, galaxySLED and MERCURIUS) are all publicly available.

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Acknowledgements

This Article makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.00597.S, ADS/JAO.ALMA#2019.1.00080.S, ADS/JAO.ALMA#2019.1.00661.S, ADS/JAO.ALMA#2019.1.01721.S and ADS/JAO.ALMA#2022.1.01473.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSTC and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. K.T. acknowledges support from JSPS KAKENHI grant numbers JP 23K03466 and 23K20870. F.E. acknowledges support from grant PRIN MIUR 2017-20173ML3WW_s and funding from the INAF Mini Grant 2022 programme ‘Face-to-Face with the Local Universe: ISM’s Empowerment (LOCAL)’. T.M. is supported by a University Research Support Grant from the National Astronomical Observatory of Japan (NAOJ). K.T. was supported by the ALMA Japan Research Grant of NAOJ ALMA Project, NAOJ-ALMA-354. Data analysis was in part carried out on the Multi-wavelength Data Analysis System operated by the Astronomy Data Center (ADC), National Astronomical Observatory of Japan.

Author information

Authors and Affiliations

  1. Faculty of Engineering, Hokkai-Gakuen University, Sapporo, Japan

    K. Tadaki

  2. National Astronomical Observatory of Japan, Mitaka, Japan

    K. Tadaki & D. Iono

  3. Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Bologna, Italy

    F. Esposito

  4. Osservatorio di Astrofisica e Scienza dello Spazio (INAF–OAS), Bologna, Italy

    F. Esposito & L. Vallini

  5. Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory, Australia

    T. Tsukui

  6. ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Canberra, Australian Capital Territory, Australia

    T. Tsukui

  7. Faculty of Global Interdisciplinary Science and Innovation, Shizuoka University, Shizuoka, Japan

    T. Saito

  8. Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), Mitaka, Japan

    D. Iono

  9. Faculty of Information Science, Shunan University, Shunan, Japan

    T. Michiyama

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Contributions

K.T. led the project and reduced the ALMA data. F.E. and L.V. supported the modelling of the CO emission and helped in the interpretation of the results. All other authors contributed to the interpretation of the results and commented on the manuscript and the ALMA proposals.

Corresponding author

Correspondence to K. Tadaki.

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Extended data

Extended Data Fig. 1 Black hole mass versus bolometric luminosity for J2310 + 1855 and other quasars at z≳5.713.

Red circles indicate quasars where compact dust emission has been detected in high-resolution ALMA observations16,17,18,19.

Extended Data Fig. 2 ALMA images of 1.4 mm continuum emission.

From left to right, the observed clean images and the dirty images after subtraction of the best-fit one- and two-component models are shown. The spatial resolution of the images is 0.050″×0.039″. Dashed and solid contours are plotted every -1σ from -5σ and every 1σ from 5σ, respectively. The effective radii of the best-fit model are shown by the magenta lines.

Extended Data Fig. 3 X-ray-dominated region model.

A gas column density (top) and X-ray flux (bottom) at different galactocentric radii. The dotted, solid, and dashed lines show the XDR models with different gas masses.

Extended Data Fig. 4 ALMA image of dust continuum emission.

The beam size is 0.08″×0.08″ (top) and 0.24″×0.24″ (bottom). The contours are plotted every 10σ from 5σ.

Extended Data Fig. 5 ALMA image of CO emission.

From left to right, the CO (J = 6-5), CO (J = 8-7), CO (J = 13-12), and CO (J = 14-13) maps are shown. The beam size is 0.08″×0.08″ (top) and 0.24″×0.24″ (bottom). The contours are plotted every 2σ from 3σ.

Extended Data Fig. 6 Visibility amplitude of [CII] emission.

Top, a wing component in in the velocity range of -465 km s-1 < v < -345 km s-1. Bottom, a disk component in in the velocity range of -315 km s-1 < v < +315 km s-1. Different symbols show different observations (Extended Data Table 1). We show the real part of the visibility as a function of uv distance along the minor axis, corresponding to the major axis in the images. The center and length of the error bars represent the mean value of the real part of the visibilities and the 1σ uncertainty. A red line and red shaded region show the best-fit model and its uncertainties, respectively.

Extended Data Table 1 Summary of ALMA observations
Full size table
Extended Data Table 2 Summary of image processing
Full size table
Extended Data Table 3 Peak flux/flux densities in the ALMA images
Full size table

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Tadaki, K., Esposito, F., Vallini, L. et al. Warm gas in the vicinity of a supermassive black hole 13 billion years ago. Nat Astron 9, 720–728 (2025). https://doi.org/10.1038/s41550-025-02505-x

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