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arxiv: 2606.28304 · v1 · pith:3BB2BBS2new · submitted 2026-06-26 · 🌌 astro-ph.GA · astro-ph.HE

SKA-VLBI view of AGN jets in the early Universe

C. Spingola , M. Mezcua , Y. Liu , S. Frey , S. Belladitta , T. An , M. Giroletti , A. Caccianiga
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A. Moretti L. Ighina T. Sbarrato G. Migliori D. Dallacasa L. I. Gurvits K. \'E. Gab\'anyi K. Perger Z. Paragi R. D. Baldi E. Ba\~nados G. Bernardi M. Bondi E. De Rubeis F. D'Ammando F. De Gasperin I. Delvecchio F. Vito K. Rubinur M. Krezinger R. Lico E. Momjian M. Orienti J. Hodgson C. Stanghellini A. Wang M. Latif H. Cao
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Pith reviewed 2026-06-29 02:57 UTC · model grok-4.3

classification 🌌 astro-ph.GA astro-ph.HE
keywords AGN jetshigh-redshift galaxiesSKA-VLBIsupermassive black holesearly universeradio interferometrycosmological geometryjet feedback
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The pith

SKA-VLBI will deliver sub-microJansky sensitivity and milliarcsecond resolution to image jetted AGN at redshifts above 6.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper argues that the Square Kilometre Array combined with very long baseline interferometry can reach the sensitivity and angular resolution required to study radio jets from active galactic nuclei in the first billion years of the Universe. These jetted sources stand out because their relativistic outflows can regulate gas in host galaxies, influence early star formation, and drive rapid growth of central supermassive black holes. The observations would place direct constraints on Doppler boosting, jet duty cycles, and jet-environment coupling at extreme redshifts, while also testing formation models that include jet-assisted super-Eddington accretion phases. The same data could refine measurements of the Universe's geometry at high precision through the properties of the sources themselves.

Core claim

SKA-VLBI observations across SKA-Mid and SKA-Low frequencies will achieve sub-μJy sensitivity together with milliarcsecond angular resolution, enabling the imaging and characterisation of compact, high-brightness-temperature radio cores in jetted AGN at z>6. This capability will directly test supermassive black hole formation and evolution models for masses above 10^6 solar masses, including possible jet-assisted super-Eddington phases, and will allow inference of the geometry of the Universe at high precision.

What carries the argument

Compact, high-brightness-temperature radio cores of jetted AGN that serve as sharp beacons for VLBI, observed with the SKA-VLBI array's combination of sensitivity and resolution at SKA frequencies.

If this is right

  • Direct constraints on Doppler boosting, jet duty cycles, and jet-environment coupling at redshifts greater than 6.
  • Tests of supermassive black hole formation models including jet-assisted super-Eddington accretion phases.
  • Inference of the geometry of the Universe at high precision from the source properties.
  • Panchromatic characterisation of host galaxies through synergies with multi-band facilities.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Detection of a substantial population would imply higher early jet activity than many current models assume, affecting estimates of black hole seed formation rates.
  • The resolved jet structures could help distinguish whether jets play a dominant role in regulating star formation in the first galaxies.
  • Cross-matching with future optical or X-ray surveys would test whether the radio-selected sources represent a distinct evolutionary channel for the earliest black holes.

Load-bearing premise

The SKA-VLBI array will actually reach the quoted sensitivity and milliarcsecond resolution at the frequencies needed for z>6 sources, and enough such jetted AGN exist to form statistically useful samples.

What would settle it

A completed SKA-VLBI survey that reaches sub-μJy levels yet detects no jetted AGN above redshift 6 or fails to resolve any milliarcsecond-scale jet structures would show the proposed capability does not materialise.

Figures

Figures reproduced from arXiv: 2606.28304 by A. Caccianiga, A. Moretti, A. Wang, C. Spingola, C. Stanghellini, D. Dallacasa, E. Ba\~nados, E. De Rubeis, E. Momjian, F. D'Ammando, F. De Gasperin, F. Vito, G. Bernardi, G. Migliori, H. Cao, I. Delvecchio, J. Hodgson, K. \'E. Gab\'anyi, K. Perger, K. Rubinur, L. Ighina, L. I. Gurvits, M. Bondi, M. Giroletti, M. Krezinger, M. Latif, M. Mezcua, M. Orienti, R. D. Baldi, R. Lico, S. Belladitta, S. Frey, T. An, T. Sbarrato, Y. Liu, Z. Paragi.

Figure 1
Figure 1. Figure 1: BH radio flux densities estimated from the fundamental plane of BH accretion (Merloni et al. 2003, MER03; Körding et al. 2006, KOR06; Gültekin et al. 2009, GUL09; Plotkin et al. 2012, PLT12; Bonchi et al. 2013, BON13; Gültekin et al. 2019, GUL19) for a spectral index 𝛼 = 0.7 (solid) and 𝛼 = 0.3 (dotted) from z = 6–14.5 at SKA-MID bands 1 (500 MHz), 2 (1.5 GHz), 5a (2.5 GHz), and 5b (6.5 GHz). The dashed, d… view at source ↗
Figure 2
Figure 2. Figure 2: A dropout radio source at 𝑧 = 7: photometry and spectrum of the quasar J0410−0139. The greyscale postage stamps show optical images, while the radio panels show the 1995 NVSS and the 2021 VLA 1.4 GHz images, both at 1.4 GHz. The 2021 VLA observations at 1.4 GHz, shown at the same size for comparison, confirms the presence of a single radio source in the field with clear evidence of variability (also confir… view at source ↗
Figure 3
Figure 3. Figure 3: The role of VLBI observations in disentangling AGN radio emission. Left: VLA map at 1.4 GHz for the quasar J2242+0334. The contour levels are at [−1, 2, 4, 6] times the RMS noise (24.7 𝜇Jy/beam). Right: 1 ′′ × 1 ′′ VLBA image at 1.5 GHz, zooming into the central area of the VLA map. In both images, the synthesized beam is shown at the bottom left corner. For both panels, the black plus sign denotes the opt… view at source ↗
Figure 4
Figure 4. Figure 4: Example of how VLBI can spatially resolve the jet structure in the source PSO J0309+27 at 𝑧 = 6.1 (adapted from Belladitta et al. 2020 and Spingola et al. 2020). The restoring beam relative to each observation and the observing frequencies are reported directly in the figure. The three VLBI bands shown here correspond to the SKA Band 2, Band 5a and Band 5b. 14 [PITH_FULL_IMAGE:figures/full_fig_p014_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Simulated 𝑢𝑣−coverage of a 12-hour observation at 1.4 GHz (Band 2) SKA-Mid AA4 with the European VLBI Network antennas (Effelsberg, Irbene, Jodrell Bank, Medicina, Noto, Sardinia, Onsala, Tianma, Torun, Urumqi and Westerbork). In red we highlight the baselines to SKA-Mid AA4. The three panels show the 𝑢𝑣−coverage for a source at a Declination of −10, 0 and 10 degrees (from left to right, respectively). in … view at source ↗
Figure 6
Figure 6. Figure 6: Simulated core–jet structure of a radio AGN at a given fixed arbitrary observing frequency (e.g. 1.6 GHz), as moved to higher redshifts and consequently to (1 + 𝑧) times higher emitted frequencies. The steep-spectrum jet emission becomes gradually weaker compared to the flat-spectrum core at (0, 0). The coordinate scales are in mas. There is one more way the Universe complicates our efforts to measure jet … view at source ↗
read the original abstract

Active Galactic Nuclei (AGN) are among the brightest sources in the Universe, and those that are also jetted are uniquely valuable at the earliest epochs, because their relativistic outflows can regulate the gas supply of their host galaxies, potentially affecting both early star formation and the rapid growth of supermassive black holes (SMBHs). Their compact, high-brightness-temperature radio cores provide the sharpest beacons for very long baseline interferometry (VLBI), enabling direct constraints on Doppler boosting, jet duty cycles, and jet$-$environment coupling at extreme redshifts. In this White Paper, we discuss how the SKA-VLBI will provide sub-$\mu$Jy sensitivity together with milliarcsecond (mas) angular resolution to image and characterise jetted AGN at $z>6$ across SKA-Mid and SKA-Low frequencies. These observations can directly test SMBHs ($>10^6$ M$_{\odot}$) formation/evolution models (including jet-assisted super-Eddington phases) and infer the geometry of the Universe, directly probing the cosmological framework at high precision. Synergies with current and next-generation multi-band facilities will also be crucial to fully understand their host galaxies and their environment, providing an unprecedented panchromatic knowledge of the first jetted AGN.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 1 minor

Summary. This white paper outlines the prospective scientific capabilities of the SKA-VLBI array for studying jetted AGN at z>6. It claims that the array will deliver sub-μJy sensitivity combined with milliarcsecond angular resolution across SKA-Mid and SKA-Low bands, enabling direct imaging and characterization of these sources to test SMBH formation and evolution models (including jet-assisted super-Eddington accretion), constrain jet duty cycles and environment coupling, and provide cosmological constraints via geometry inference, with synergies to multi-wavelength facilities.

Significance. If the projected performance is achieved and a sufficient population of z>6 jetted AGN is available, the work identifies valuable future science cases for early-universe AGN jet studies that are currently inaccessible. The explicit discussion of synergies with next-generation facilities strengthens the case for coordinated observing strategies.

minor comments (1)
  1. [Abstract] Abstract: the statement that observations will 'infer the geometry of the Universe, directly probing the cosmological framework at high precision' would benefit from a short parenthetical note or reference clarifying the intended method (e.g., via angular-size or proper-motion measurements).

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive review, supportive assessment of the science case, and recommendation to accept the manuscript. No major comments were raised.

Circularity Check

0 steps flagged

No derivations, equations or fitted parameters; white paper on prospective instrument capabilities

full rationale

The supplied text is a white paper outlining expected SKA-VLBI performance for z>6 jetted AGN. It contains no equations, no fitted parameters, no derivation chain, and no self-citations invoked as load-bearing uniqueness theorems or ansatzes. All statements are forward-looking engineering and demographic projections framed as discussion points rather than proven results derived from prior steps within the paper. No step reduces to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are introduced; the text relies on standard assumptions about future telescope performance.

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Works this paper leans on

18 extracted references · 18 canonical work pages · 3 internal anchors

  1. [1]

    URLhttps://arxiv.org/abs/2603.21119. T. An et al.Nature Communications, 11:143, Jan. 2020a. doi: 10.1038/s41467-019-14093-2. T.An,Y.Zhang,andS.Frey.MonthlyNoticesoftheRoyalAstronomicalSociety,497(2):2260–2264, Sept. 2020b. doi: 10.1093/mnras/staa2132. E. Bañados et al.Astrophysical Journal Letters, 805(1):L8, May 2015a. doi: 10.1088/2041-8205/ 805/1/L8. 2...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1038/s41467-019-14093-2 2041

  2. [2]

    R.H.Becker,R.L.White,andD.J.Helfand

    doi: 10.1093/mnras/stab2613. R.H.Becker,R.L.White,andD.J.Helfand. InD.R.Crabtree,R.J.Hanisch,andJ.Barnes,editors, Astronomical Data Analysis Software and Systems III, volume 61 ofAstronomical Society of the Pacific Conference Series, page 165, Jan. 1994. S. Belladitta et al.Astronomy and Astrophysics, 635:L7, Mar. 2020. doi: 10.1051/0004-6361/ 201937395. ...

    work page doi:10.1093/mnras/stab2613 1994

  3. [3]

    doi: 10.1093/mnras/sty3526. A. Caccianiga et al.Astronomy and Astrophysics, 684:A98, Apr. 2024. doi: 10.1051/0004-6361/ 202348561. H. M. Cao et al.Monthly Notices of the Royal Astronomical Society, 467(1):950–960, May 2017a. doi: 10.1093/mnras/stx160. S. Cao et al.Astronomy and Astrophysics, 606:A15, Sept. 2017b. doi: 10.1051/0004-6361/ 201730551. 22 SKA–...

    work page doi:10.1093/mnras/sty3526 2024

  4. [4]

    doi: 10.1093/mnras/stae1732. K. J. Duncan et al.Monthly Notices of the Royal Astronomical Society, 522(3):4548–4564, July

    work page doi:10.1093/mnras/stae1732

  5. [5]

    R.Endsleyetal.MonthlyNoticesoftheRoyalAstronomicalSociety,512(3):4248–4261,May2022

    doi: 10.1093/mnras/stad1267. R.Endsleyetal.MonthlyNoticesoftheRoyalAstronomicalSociety,512(3):4248–4261,May2022. doi: 10.1093/mnras/stac737. R.Endsleyetal.MonthlyNoticesoftheRoyalAstronomicalSociety,520(3):4609–4620,Apr.2023. doi: 10.1093/mnras/stad266. Euclid Collaboration et al.Astronomy and Astrophysics, 662:A112, June 2022. doi: 10.1051/ 0004-6361/202...

    work page doi:10.1093/mnras/stad1267 2023

  6. [6]

    S.Frey,L.Mosoni,Z.Paragi,andL.I.Gurvits.MonthlyNoticesoftheRoyalAstronomicalSociety, 343(1):L20–L24, July 2003

    doi: 10.1051/0004-6361/202556447. S.Frey,L.Mosoni,Z.Paragi,andL.I.Gurvits.MonthlyNoticesoftheRoyalAstronomicalSociety, 343(1):L20–L24, July 2003. doi: 10.1046/j.1365-8711.2003.06869.x. S. Frey et al.Astronomy and Astrophysics, 524:A83, Dec. 2010. doi: 10.1051/0004-6361/ 201015554. S.Freyetal.AstronomyandAstrophysics,531:L5,July2011. doi: 10.1051/0004-6361...

    work page doi:10.1051/0004-6361/202556447 2003

  7. [7]

    doi: 10.1093/mnras/stt637. G. Ghisellini et al.Monthly Notices of the Royal Astronomical Society, 438(3):2694–2700, Mar

    work page doi:10.1093/mnras/stt637

  8. [8]

    doi: 10.1093/mnras/stt2394. M. Ghodsi Yengejeh et al.arXiv e-prints, art. arXiv:2604.12936, Apr. 2026. doi: 10.48550/arXiv. 2604.12936. R. Gilli et al.Astronomy and Astrophysics, 666:A17, Oct. 2022. doi: 10.1051/0004-6361/ 202243708. 24 SKA–VLBI view of AGN jets in the early Universe C. Spingola et al. A. J. Gloudemans et al.Astronomy and Astrophysics, 65...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stt2394 2026

  9. [9]

    doi: 10.1093/mnras/staf622. R. H. Hildebrand.Quarterly Journal of the Royal Astronomical Society, 24:267–282, Sept. 1983. J. A. Hodgson et al.Monthly Notices of the Royal Astronomical Society, 495(1):L27–L31, June

    work page doi:10.1093/mnras/staf622 1983

  10. [10]

    T.Hovattaetal.AstronomicalJournal,147(6):143,June2014

    doi: 10.1093/mnrasl/slaa051. T.Hovattaetal.AstronomicalJournal,147(6):143,June2014. doi: 10.1088/0004-6256/147/6/143. L. Ighina et al.Astrophysical Journal Letters, 990(2):L56, Sept. 2025a. doi: 10.3847/2041-8213/ aded0a. 25 SKA–VLBI view of AGN jets in the early Universe C. Spingola et al. L. Ighina et al.Astronomy and Astrophysics, 698:A158, June 2025b....

    work page doi:10.1093/mnrasl/slaa051 2041

  11. [11]

    doi: 10.1093/mnras/stad1813. E. Körding, H. Falcke, and S. Corbel.Astronomy and Astrophysics, 456(2):439–450, Sept. 2006. doi: 10.1051/0004-6361:20054144. Y. Kovalev et al. InAdvancing Astrophysics with the SKA – II (AASKAII). 2026. arXiv search: Report number AASKAII/Kovalev01. Y. Y. Kovalev et al.Astronomical Journal, 130(6):2473–2505, Dec. 2005. doi: 1...

    work page doi:10.1093/mnras/stad1813 2006

  12. [12]

    A., Chandler, C

    doi: 10.1088/1538-3873/ab63eb. R.L.Larsonetal.AstrophysicalJournalLetters,953(2):L29,Aug.2023. doi: 10.3847/2041-8213/ ace619. M. A. Latif, D. J. Whalen, and M. Mezcua.Monthly Notices of the Royal Astronomical Society, 527(1):L37–L41, Jan. 2024. doi: 10.1093/mnrasl/slad102. M. A. Latif, A. Aftab, D. J. Whalen, and M. Mezcua.Astronomy and Astrophysics, 694...

    work page doi:10.1088/1538-3873/ab63eb 2023

  13. [13]

    doi: 10.1051/0004-6361/202453194. S.-S. Lee.Journal of Korean Astronomical Society, 47(6):303–309, Dec. 2014. doi: 10.5303/ JKAS.2014.47.6.303. Y. Li et al.Research in Astronomy and Astrophysics, 24(7):072001, July 2024. doi: 10.1088/ 1674-4527/ad420c. M. L. Lister et al.Astrophysical Journal, 874(1):43, Mar. 2019. doi: 10.3847/1538-4357/ab08ee. Y. Liu et...

    work page doi:10.1051/0004-6361/202453194 2014

  14. [14]

    doi: 10.1093/mnras/stab1998. M. Magliocchetti.Astronomy and Astrophysics Review, 30(1):6, Dec. 2022. doi: 10.1007/ s00159-022-00142-1. R. Maiolino et al.Nature, 544(7649):202–206, Mar. 2017. doi: 10.1038/nature21677. R. Maiolino et al.Nature, 627(8002):59–63, Mar. 2024. doi: 10.1038/s41586-024-07052-5. A. Marconi et al.Monthly Notices of the Royal Astrono...

    work page doi:10.1093/mnras/stab1998 2022

  15. [15]

    doi: 10.1051/0004-6361/201629832. J. Matthee et al.Astrophysical Journal, 963(2):129, Mar. 2024. doi: 10.3847/1538-4357/ad2345. J. H. Mayo et al.Astronomy and Astrophysics, 539:A33, Mar. 2012. doi: 10.1051/0004-6361/ 201118254. 27 SKA–VLBI view of AGN jets in the early Universe C. Spingola et al. G. Mazzolari et al.Astronomy and Astrophysics, 687:A120, Ju...

    work page doi:10.1051/0004-6361/201629832 2024

  16. [16]

    doi: 10.1093/mnras/sty1776. S. Murthy et al.Nature Astronomy, 6:488–495, Feb. 2022. doi: 10.1038/s41550-021-01596-6. M.Neelemanetal.AstrophysicalJournal,911(2):141,Apr.2021. doi: 10.3847/1538-4357/abe70f. Á.A.Orsi,N.Fanidakis,C.G.Lacey,andC.M.Baugh.MonthlyNoticesoftheRoyalAstronomical Society, 456(4):3827–3839, Mar. 2016. doi: 10.1093/mnras/stv2919. F. Pa...

    work page internal anchor Pith review doi:10.1093/mnras/sty1776 2022

  17. [17]

    doi: 10.3847/1538-4357/ab4999. G. Risaliti et al.Astronomische Nachrichten, 344(4):e20230054, May 2023. doi: 10.1002/asna. 20230054. J. Roland et al.Classical and Quantum Gravity, 10:S251–S254, Dec. 1993. doi: 10.1088/ 0264-9381/10/S/040. N. Roy et al.Astrophysical Journal, 970(1):69, July 2024. doi: 10.3847/1538-4357/ad4bda. M. Ruszkowski and V. Springel...

    work page doi:10.3847/1538-4357/ab4999 2023

  18. [18]

    doi: 10.1093/mnras/stab2121. M. Yue et al.Astrophysical Journal Letters, 974(2):L26, Oct. 2024a. doi: 10.3847/2041-8213/ ad7eba. M. Yue et al.Astrophysical Journal, 966(2):176, May 2024b. doi: 10.3847/1538-4357/ad3914. G. R. Zeimann et al.Astrophysical Journal, 736(1):57, July 2011. doi: 10.1088/0004-637X/736/ 1/57. Y. Zhang et al.Astrophysical Journal, 9...

    work page doi:10.1093/mnras/stab2121 2041