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arxiv: 2606.31773 · v1 · pith:YYW6DCRZnew · submitted 2026-06-30 · 🌌 astro-ph.GA

Uncovering neutral Hydrogen clouds in Radio Galaxies in the SKA era

Mamta Pandey-Pommier This is my paper

Pith reviewed 2026-07-01 04:17 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords neutral hydrogenHI 21-cm lineradio galaxiesAGN feedbackjet-ISM interactionSKA-VLBIparsec-scale imagingcold gas kinematics
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The pith

SKA-VLBI will resolve neutral hydrogen at parsec scales around radio jets to map atomic gas kinematics in AGN feedback sites.

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

The paper argues that arcsecond-scale observations cannot link neutral hydrogen to specific structures like circumnuclear disks, jet outflows, or compressed layers in active galaxies. It focuses on molecular gas-rich radio AGN with large jets and strong plasma-ISM interactions as the best targets where atomic, molecular, and ionized gas coexist. SKA-VLBI's milliarcsecond resolution and microJansky sensitivity will image HI 21-cm emission on parsec scales from nuclear regions out to kiloparsec jet interaction zones. This will determine whether the gas is inflowing, outflowing, or otherwise disturbed, directly testing how radio jets regulate cold interstellar medium. The result matters for models of AGN feedback and galaxy evolution because it connects atomic gas properties to multiphase interactions.

Core claim

In molecular gas-rich radio AGN hosting large-scale jets with strong interactions between the radio plasma and the surrounding ISM, SKA-VLBI will deliver milliarcsecond-scale imaging and μJy-level sensitivity, resolving HI gas clouds on parsec scales across extended radio structures and enabling detailed constraints on the location, morphology, and kinematics of atomic gas from the nuclear regions to kiloparsec-scale jet-ISM interaction sites.

What carries the argument

SKA-VLBI milliarcsecond imaging of the HI 21-cm line in systems where atomic, molecular, and ionized gas coexist near radio jets.

If this is right

  • HI will be mapped as associated with circumnuclear structures, jet-driven outflows, compressed gas layers, or fragmented clouds in a disturbed multiphase ISM.
  • Kinematics measurements will distinguish inflowing, outflowing, or otherwise disturbed atomic gas components.
  • Combined with molecular gas data at other wavelengths, the observations will give a full view of jet-ISM interactions and AGN-driven feedback on cold gas.
  • This will quantify the role of cold gas in regulating galaxy evolution through AGN feedback.

Where Pith is reading between the lines

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

  • The approach could be extended to compare HI distributions across different jet powers or galaxy types to test feedback efficiency.
  • Non-detections in some targets might reveal selection effects or new gas phases not captured by current models.
  • The same targets could serve as benchmarks for hydrodynamic simulations of multiphase gas in radio galaxies.

Load-bearing premise

Suitable target systems exist that are molecular gas-rich radio AGN with large-scale jets and strong plasma-ISM interactions where atomic, molecular, and ionized gas coexist.

What would settle it

Targeted SKA-VLBI observations of a sample of such radio AGN that fail to detect or resolve HI structures at parsec scales near jet-ISM interaction sites would show the claimed constraints on gas location and kinematics cannot be achieved.

Figures

Figures reproduced from arXiv: 2606.31773 by Mamta Pandey-Pommier.

Figure 1
Figure 1. Figure 1: Panel 1 & 2:Cold gas as observed with ALMA Oosterloo et al. (2023) and H i and CO profiles measured in 3C84 Morganti et al. (2023). limited to small samples due to sensitivity and frequency constraints. Further, the interactions encountered by the jet within the ISM are often imprinted in its morphology as bent or distorted asymmetries with wiggles, knots, or disrupted lobes that can be traced via continuu… view at source ↗
Figure 2
Figure 2. Figure 2: Panel 1 & 2:HI gas outflows as observed with VLBI in IC 15063 (Oosterloo et al., 2023) and 4C 12.50 (Morganti et al., 2004). Panel 3: 3C326: Map of N(H i)𝑇 −1 spin for H i features detected with the EVN (Schulz et al., 2018). Subsequent studies confirmed that such jet-driven atomic gas structures are common in compact and restarting radio sources. In compact radio galaxy, 4C 12.50, Morganti et al. (2004) u… view at source ↗
Figure 3
Figure 3. Figure 3: H i gas clouds and outflows measured via VLBI imaging observations on AGNs. powers. These plots offer valuable insights into the trends and variations in AGN feedback processes, as well as the influence of AGN jets on the surrounding ISM. Panel 1 reveals a broad range of values for both cloud velocity and radio power, reflecting the complex interplay between several factors, including jet morphology, jet p… view at source ↗
Figure 4
Figure 4. Figure 4: Panel 1:Baseline sensitivity for different SKA1-MID subarrays configurations and a 100m class remote telescope, for different observing bandwidths - adapted from - https://www.skao.int/sites/default/files/documents/JJ-WP10deliverable10.3.pdf. Panel 2 and 3: N(H i) sen￾sitivities for SKA and pathfinders w.r.t to detect cold gas in MOHEGs for different integration times (Wagh et al., 2024). SKA1-MID will ach… view at source ↗
read the original abstract

AGN feedback driven by radio jets plays a key role in regulating the cold ISM of galaxies. Neutral hydrogen traced through the H1 21-cm line provides a powerful probe of the kinematics, distribution, and physical conditions of cold gas in the central regions of AGN. Previous observations have detected H1 column densities down to $\sim10^{20}$ cm$^{-2}$, but typically at arcsecond-scale resolution, inhibiting the characterization of small-scale H1 gas clouds and their connection to molecular gas reservoirs and sites of jet-ISM interaction. High-resolution H1 imaging is therefore required to determine whether the atomic gas is associated with circumnuclear structures, jet-driven outflows, compressed gas layers, or fragmented cold clouds embedded within a disturbed multiphase ISM. In this chapter, we focus on molecular gas-rich radio AGN hosting large-scale jets and exhibiting strong interactions between the radio plasma and the surrounding ISM, where atomic, molecular, and ionized gas coexist. These systems provide ideal laboratories for investigating the spatial distribution and kinematics of H1, constraining the impact of radio jets on the cold gas, and determining whether the gas is associated with inflowing, outflowing, or otherwise disturbed components. SKA-VLBI will deliver milliarcsecond-scale imaging and $\mu$Jy-level sensitivity, resolving H1 gas clouds on parsec scales across extended radio structures. This capability will enable detailed constraints on the location, morphology, and kinematics of atomic gas from the nuclear regions to kiloparsec-scale jet-ISM interaction sites. Combined with molecular gas observations at other wavelengths, these measurements will provide a comprehensive view of the jet-ISM interactions, the impact of AGN-driven feedback, and the role of cold gas in galaxy evolution.

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 / 2 minor

Summary. The manuscript is a prospective review chapter motivating high-resolution neutral hydrogen (HI) 21-cm imaging with SKA-VLBI in molecular gas-rich radio AGN hosting large-scale jets and exhibiting strong jet-ISM interactions. It claims that prior arcsecond-scale detections (down to column densities ~10^20 cm^{-2}) are insufficient to characterize small-scale HI structures and their connection to molecular gas or jet-driven processes, and that SKA-VLBI's milliarcsecond resolution and μJy sensitivity will resolve parsec-scale clouds, enabling constraints on location, morphology, and kinematics from nuclear regions to kiloparsec-scale interaction sites when combined with multi-phase gas observations.

Significance. If the described instrumental capabilities are realized, the work identifies a valuable path for probing multiphase gas in AGN feedback environments, bridging current resolution limits with the scales needed to distinguish inflow, outflow, or disturbed components. As a forward-looking review without new data, derivations, or quantitative predictions, its value is in highlighting observational strategies rather than delivering falsifiable results; the focus on coexisting atomic/molecular/ionized gas systems is logically consistent with existing literature on such AGN.

minor comments (2)
  1. [Abstract] Abstract: The notation 'H1' appears repeatedly and should be standardized to the conventional 'HI' for clarity and consistency with standard astrophysical usage.
  2. [Abstract] Abstract: Specific citations or references to the 'previous observations' of HI column densities at arcsecond scales would help readers locate the foundational results being contrasted.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript and their recommendation to accept. The review accurately captures the prospective nature of the work as a forward-looking discussion of observational strategies with SKA-VLBI.

Circularity Check

0 steps flagged

No significant circularity; purely descriptive review with no derivations

full rationale

The manuscript is a prospective review chapter focused on future SKA-VLBI observational capabilities for milliarcsecond-scale HI 21-cm imaging in radio AGN. It advances no equations, derivations, fitted parameters, quantitative predictions, or model reductions. All claims are descriptive statements about instrumental resolution and sensitivity, referencing prior literature on target systems without any self-referential fitting or load-bearing self-citation chains. The presupposition of suitable targets is drawn from external cited work and does not reduce to an internal definition or construction within this paper. This is the standard case of a self-contained descriptive text with no derivation chain to inspect.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are introduced because the document is a review chapter focused on future observational strategy rather than any quantitative model or derivation.

pith-pipeline@v0.9.1-grok · 5839 in / 1110 out tokens · 40635 ms · 2026-07-01T04:17:09.385570+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

20 extracted references · 18 canonical work pages · 4 internal anchors

  1. [1]

    10 Uncovering Hiclouds in Radio Galaxies in the SKA era M

    doi: https://doi.org/10.1093/mnras/sty2184. 10 Uncovering Hiclouds in Radio Galaxies in the SKA era M. Pandey-Pommier et al. J.N.H.S.Aditya,H.Yoon,J.R.Allison,etal.MonthlyNoticesoftheRoyalAstronomicalSociety, 527(3):8511–8534, Jan

    work page doi:10.1093/mnras/sty2184

  2. [2]

    doi: 10.1093/mnras/stad3722. C. Cicone et al.Astronomy & Astrophysics, 562:A21,

    work page doi:10.1093/mnras/stad3722

  3. [3]

    doi: 10.1051/0004-6361/201322464. S. J. Curran.Publications of the Astronomical Society of Australia, 41, Feb

    work page internal anchor Pith review doi:10.1051/0004-6361/201322464

  4. [4]

    D.S.DeYoung, M.S.Roberts, andW.C.Saslaw.TheAstrophysicalJournal, 185:809–815,

    doi: 10.1017/ pasa.2024.1. D.S.DeYoung, M.S.Roberts, andW.C.Saslaw.TheAstrophysicalJournal, 185:809–815,

    2024

  5. [5]

    doi: 10.1086/152456. R. D. Ekers, J. M. van der Hulst, and G. K. Miley.Nature, 262:369–370,

    work page doi:10.1086/152456

  6. [6]

    doi: 10.48550/arXiv.1708.07371. T. M. Heckman and P. N. Best.Annual Review of Astronomy and Astrophysics, 52:589–660,

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.1708.07371

  7. [7]

    doi: 10.1146/annurev-astro-081913-035722. M. R. Krumholz.Physics Reports, 539:49–134, June

    work page internal anchor Pith review doi:10.1146/annurev-astro-081913-035722

  8. [8]

    doi: 10.48550/arXiv.1402.0867. R. A. Laing and A. H. Bridle.Monthly Notices of the Royal Astronomical Society, 437(4):3405– 3441,

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.1402.0867

  9. [9]

    A.K.Leroy,F.Walter,E.Brinks,andetal.TheAstronomicalJournal,136:2782–2845,Dec.2008

    doi: 10.1093/mnras/stt2138. A.K.Leroy,F.Walter,E.Brinks,andetal.TheAstronomicalJournal,136:2782–2845,Dec.2008. doi: 10.1088/0004-6256/136/6/2782. Y. Li et al.Research in Astronomy and Astrophysics, Apr

    work page doi:10.1093/mnras/stt2138 2008

  10. [10]

    doi: 10.1051/0004-6361/201730563. F. M. Maccagni et al.Astronomy & Astrophysics, 675:A59,

    work page doi:10.1051/0004-6361/201730563

  11. [12]

    doi: 10.3389fspas.2017. 00042. R.Morganti, T.A. Oosterloo, et al.TheAstrophysical Journal, 593:L69–L72,

    2017

  12. [14]

    11 Uncovering Hiclouds in Radio Galaxies in the SKA era M

    doi: 10.1051/0004-6361:200500197. 11 Uncovering Hiclouds in Radio Galaxies in the SKA era M. Pandey-Pommier et al. R.Morganti,S.Veilleux,etal.Astronomy&Astrophysics,593:11,2016. doi: 10.1051/0004-6361/ 201628978. R.Morgantietal.Astronomy&Astrophysics,678:A42,2023. doi: 10.1051/0004-6361/202347117. URLhttps://doi.org/10.1051/0004-6361/202347117. P. M. Ogle...

    work page doi:10.1051/0004-6361:200500197 2016

  13. [15]

    doi: 10.1088/0004-637X/ 724/2/1193. T. Oosterloo, R. Morganti, and S. Murthy.Nature Astronomy, 7(12):1506–1513,

    work page doi:10.1088/0004-637x/

  14. [16]

    Nature Astronomy , keywords =

    doi: 10.1038/s41550-023-02138-y. URLhttps://doi.org/10.1038/s41550-023-02138-y. T. A. Oosterloo, R. Morganti, C. Tadhunter, et al.A&A, 700(1),

    work page doi:10.1038/s41550-023-02138-y

  15. [17]

    700+ nights of photometry

    doi: 10.1051/0004-6361/ 202554536. M.Pandey-Pommieretal. Tracinggasoutflowsinmolecularhydrogenemission-richgalaxieswith the ska. InAdvancing Astrophysics with the SKA – II (AASKAII)

    work page doi:10.1051/0004-6361/

  16. [18]

    doi: https: //doi.org/10.1051/0004-6361/201833108. J. Silk and M. J. Rees.Astronomy and Astrophysics, 331:L1–L4,

    work page doi:10.1051/0004-6361/201833108

  17. [19]

    doi: 10.1007/s00159-016-0094-x

    C.Tadhunter.AstronomyandAstrophysicsReview,24:10,2016. doi: 10.1007/s00159-016-0094-x. S. Veilleux, G. Cecil, and J. Bland-Hawthorn.Annual Review of Astronomy and Astrophysics, 43: 769–826,

    work page doi:10.1007/s00159-016-0094-x 2016

  18. [20]

    doi: 10.1146/annurev.astro.43.072103.150610. R. C. Vermeulen et al.Astronomy & Astrophysics, 404:861–875,

    work page doi:10.1146/annurev.astro.43.072103.150610

  19. [21]

    doi: 10.1051/0004-6361: 20030468. S. Wagh, M. Pandey-Pommier, N. Roy, et al.The Astrophysical Journal, 963(2):11pp, Mar

    work page doi:10.1051/0004-6361:

  20. [22]

    and Pandey-Pommier, M and Roy, Nirupam and others , title =

    doi: 10.3847/1538-4357/ad1edf. T.WiklindandC.Henkel.AstronomyandAstrophysics,297:L71–L74,1995. doi: https://ui.adsabs. harvard.edu/scan/manifest/1995A\&A...297L..71W. 12

    work page doi:10.3847/1538-4357/ad1edf 1995