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arxiv: 2606.25523 · v1 · pith:M74BD3JCnew · submitted 2026-06-24 · 🌌 astro-ph.GA

Studying HI and the Cosmic Web in the Era of SKA

Hengxing Pan , Martin Meyer , Madalina N. Tudorache , S. Lyla Jung , Maryam Arabsalmani , Gabriella De Lucia , Kristine Spekkens , Matt J. Jarvis This is my paper

Pith reviewed 2026-06-25 21:22 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords neutral hydrogencosmic webgalaxy evolutiongas accretionradio surveyslarge-scale structureSKA
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The pith

The Square Kilometre Array will map neutral hydrogen across galactic disks and cosmic web scales to trace gas accretion.

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

Neutral atomic hydrogen fuels galaxy growth yet the mechanisms of its accretion from larger structures remain unclear. The paper reviews recent observational and theoretical work on this topic and identifies the Square Kilometre Array as the instrument that can combine resolved imaging of individual disks with wide surveys of surrounding volumes. It argues that this dual capability will reveal how processes at cosmic web scales regulate gas supply to galaxies. Coordination with facilities at other wavelengths is presented as necessary to interpret the resulting data sets. The review therefore positions SKA observations as the next step toward a connected picture of gas flows from intergalactic to galactic scales.

Core claim

Neutral atomic hydrogen plays a central role in the evolution of galaxies, but how gas is accreted onto galactic disks and how this process is governed by the cascade of processes extending up to cosmic web scales remains poorly understood. The Square Kilometre Array has the potential to advance this understanding through its ability to resolve galactic disks with high column density sensitivity while also surveying the large volumes needed to capture cosmic web effects. The chapter examines recent observational and theoretical progress, the specific contributions expected from the SKA, and the required alignment with other radio and multiwavelength facilities.

What carries the argument

The Square Kilometre Array's combination of high-resolution, high-sensitivity HI imaging of individual galaxies with large-volume surveys that reach cosmic web scales.

If this is right

  • Resolved HI maps will directly measure gas accretion rates onto galaxy disks.
  • Wide surveys will quantify how cosmic web environment influences the HI content of galaxies.
  • Multi-facility coordination will link HI structures to stellar and molecular gas components.
  • Theoretical models of galaxy formation will face new observational tests at the interface of galactic and large-scale structure scales.

Where Pith is reading between the lines

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

  • The same data sets could serve as tracers for testing how baryons trace the underlying dark matter distribution on megaparsec scales.
  • Comparisons with existing smaller HI surveys would allow direct measurement of the improvement in sensitivity and volume coverage.
  • If the expected correlations appear, they would constrain the efficiency of gas cooling and inflow in different cosmic environments.

Load-bearing premise

Current observational and theoretical limitations can be overcome primarily through the SKA's combination of resolution and survey volume.

What would settle it

SKA data that show no measurable correlation between galactic HI accretion rates and the positions or properties of cosmic web filaments at the scales predicted by current models.

Figures

Figures reproduced from arXiv: 2606.25523 by Gabriella De Lucia, Hengxing Pan, Kristine Spekkens, Madalina N. Tudorache, Martin Meyer, Maryam Arabsalmani, Matt J. Jarvis, S. Lyla Jung.

Figure 1
Figure 1. Figure 1: Simulated stellar (red) and H i distribution (blue) within a box of 300 × 300 × 30 comoving Mpc at 𝑧 = 0 in the left and right, respectively. The large-scale structures such as galaxy filaments and groups are clearly perceivable visually. The simulation is based on the IllustrisTNG-300 project (Nelson et al., 2021). of the cosmic web. However, whilst Kraljic et al. (2020) find a spin transition for a stell… view at source ↗
Figure 2
Figure 2. Figure 2: Left: H i column density sensitivity (3𝜎 over 16 km s−1 ) as a function of redshift for the three mock SKA AA4 surveys color-coded by the target time of 5, 20 and 80 minutes per pointing. Right: Spatial resolution as a function of redshift for six angular resolution scales of 3, 4, 10, 30, 80 and 229 arcsec. The performance figures are estimated at a declination of -30 degrees and an observing frequency of… view at source ↗
Figure 3
Figure 3. Figure 3: Left: H i mass threshold (5𝜎) as a function of redshift for the four mock surveys color-coded by the target time of 5, 20 and 80 minutes per pointing with blue, orange and green corresponding to an sky coverage of 4000, 1000 and 250 deg2 , respectively. The orange histogram shows the number of H i detections for SKA with 20 mins target time per pointing. The grey and black dashed lines correspond to the de… view at source ↗
Figure 4
Figure 4. Figure 4: H i source count as a function of H i mass for the mock SKA AA4 surveys. The thick and thin lines are at 𝑧 < 0.09 and 𝑧 > 0.22, respectively. The 4000 deg2 survey covers the largest space volume that is ideal for inferring the clustering strength and bias parameters of gas-rich galaxies, and we expect a detection of Baryonic Acoustic Oscillations (BAOs) from H i survey independently of the past and forthco… view at source ↗
read the original abstract

Neutral atomic hydrogen plays a central role in the evolution of galaxies. Yet our understanding of how gas is accreted onto galactic disks, and the way this is governed by the cascade of processes extending up to cosmic web scales, remains poorly understood. The Square Kilometre Array has the potential to significantly advance our understanding in this field, being able to both resolve galactic disks with high column density sensitivity, while also being able to survey the large volumes needed to understand the impact of processes at the level of the cosmic web. In this chapter, we examine recent observational and theoretical progress made in this area, the potential contribution of the SKA, and needed alignment with other radio and multiwavelength facilities to advance the field.

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 manuscript is a perspective chapter reviewing the central role of neutral atomic hydrogen (HI) in galaxy evolution, current limitations in understanding gas accretion onto disks and its regulation by cosmic-web-scale processes, recent observational and theoretical advances, the prospective capabilities of the Square Kilometre Array (SKA) for high-resolution, high-sensitivity HI imaging combined with large-volume surveys, and the importance of coordination with other radio and multiwavelength facilities.

Significance. As a forward-looking synthesis rather than a report of new data or derivations, the chapter usefully frames strategic priorities for HI and cosmic-web studies in the SKA era. It may help orient the community toward coordinated observing programs, though its impact rests on the accuracy of the high-level assessment of SKA capabilities rather than on any falsifiable prediction or parameter-free result.

minor comments (1)
  1. [Abstract] The abstract states that the chapter will 'examine recent observational and theoretical progress' but does not preview the specific sub-topics or structure that follow; adding a brief roadmap sentence would improve readability for readers scanning the piece.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their thorough and positive assessment of the manuscript. We are pleased that the review recognizes the chapter as a useful forward-looking synthesis framing strategic priorities for HI and cosmic-web studies in the SKA era, and we appreciate the recommendation to accept.

Circularity Check

0 steps flagged

No significant circularity; high-level review with no derivations

full rationale

The manuscript is a perspective chapter that reviews recent observational and theoretical progress on HI and the cosmic web, discusses SKA's prospective capabilities, and notes needed alignment with other facilities. It advances no original empirical results, equations, derivations, or falsifiable predictions. No load-bearing steps exist that could reduce to self-citation chains, fitted inputs, or self-definitional constructs. The discussion is framed as prospective rather than demonstrated, making the paper self-contained against external benchmarks with no circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The paper is a review and does not introduce new free parameters, axioms, or invented entities; it summarizes literature and outlines future observational potential.

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