pith. sign in

arxiv: 2606.30947 · v1 · pith:KE4S7GJ2new · submitted 2026-06-29 · 🌌 astro-ph.CO · astro-ph.GA

Square Kilometer Array Synergies for the Epoch of Reionization and Cosmic Dawn

Anirban Chakraborty , Tirthankar R. Choudhury , Kanan K. Datta , Pratika Dayal , Jiten Dhandha , Samuel Gagnon-Hartman , Sambit K. Giri , Adelie Gorce
show 10 more authors
Caroline Heneka Anne Hutter Barun Maity Suman Majumdar Andrei Mesinger Kana Moriwaki Chandra Shekhar Murmu Yuxiang Qin Shintaro Yoshiura Erik Zackrisson
This is my paper

Pith reviewed 2026-07-01 00:55 UTC · model grok-4.3

classification 🌌 astro-ph.CO astro-ph.GA
keywords Epoch of ReionizationCosmic Dawn21-cm signalSquare Kilometer Arraysynergiescross-correlationsintergalactic mediumforeground mitigation
0
0 comments X

The pith

Synergies with other instruments are essential for SKA to detect and interpret the cosmic 21-cm signal from the Epoch of Reionization and Cosmic Dawn.

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

The paper argues that observations from other instruments will be crucial for the Square Kilometer Array to successfully detect the faint 21-cm signal emitted during the Epoch of Reionization and Cosmic Dawn. These synergies can supply prior knowledge about galaxies and the intergalactic medium, help overcome foreground contamination through cross-correlations, and deliver additional understanding of how galaxies interact with their surrounding gas. The review examines existing synergy efforts and identifies the types of complementary observations that would best support SKA-low measurements in this area.

Core claim

Synergies with other instruments will be essential in making, verifying, and interpreting a detection of the cosmic 21-cm signal from the Epoch of Reionization and Cosmic Dawn with the Square Kilometer Array telescope, as they provide prior information about galaxies and the IGM, mitigate foregrounds and systematics through cross-correlations, and give complementary physical insights into the galaxy-IGM connection.

What carries the argument

Cross-correlations between SKA 21-cm data and observations from other wavelengths or instruments to mitigate foregrounds and systematics.

If this is right

  • Prior information about galaxies and the IGM during EoR/CD can be obtained from complementary observations.
  • Cross-correlations can pave the road to a first 21cm detection by mitigating foregrounds and systematics.
  • Complementary physical insights into the galaxy-IGM connection can be gained.
  • Future observations should be chosen to best complement SKA-low EoR/CD data.

Where Pith is reading between the lines

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

  • If cross-correlations prove effective, multi-messenger strategies for early universe observations will become standard practice.
  • Coordinated surveys across radio, optical, and X-ray facilities could accelerate progress on reionization studies.
  • Current pathfinder telescopes might already be used to test these synergy approaches before full SKA deployment.

Load-bearing premise

That cross-correlations with external observations can effectively mitigate foregrounds and systematics in the 21-cm observations.

What would settle it

An experiment showing that cross-correlating SKA-like 21-cm data with galaxy surveys or other tracers does not reduce the foreground contamination or reveal the signal as expected.

Figures

Figures reproduced from arXiv: 2606.30947 by Adelie Gorce, Andrei Mesinger, Anirban Chakraborty, Anne Hutter, Barun Maity, Caroline Heneka, Chandra Shekhar Murmu, Erik Zackrisson, Jiten Dhandha, Kana Moriwaki, Kanan K. Datta, Pratika Dayal, Sambit K. Giri, Samuel Gagnon-Hartman, Shintaro Yoshiura, Suman Majumdar, Tirthankar R. Choudhury, YuXiang Qin.

Figure 1
Figure 1. Figure 1: The progress of reionization and the associated evolution of Lyman Alpha Emitter (LAE) visibility between 𝑧 ∼ 8 and 𝑧 ∼ 6.6, from left to right, as marked (Hutter et al., 2023b). The upper and lower rows show results for scenarios in which 𝑓esc decreases (mhdec) and increases (mhinc) with an increase in halo mass, respectively. EoR morphology is much richer in small-scale structures when low-mass sources d… view at source ↗
Figure 2
Figure 2. Figure 2: Constraints on the reionization history of the intergalactic medium from multiple observational probes. Different Lyman-𝛼 observations constrain the ionization fraction as a function of redshift, including: the dark pixel fraction in quasar spectra (McGreer et al., 2015; Jin et al., 2023), Lyman-𝛼 damping wing profiles (Greig et al., 2022; Curtis-Lake et al., 2023; Hsiao et al., 2024; Umeda et al., 2024; M… view at source ↗
Figure 3
Figure 3. Figure 3: Constraints on the redshift evolution of the 21-cm power spectrum at 𝑘 = 0.13 cMpc−1 , the 21- cm global signal and mean neutral fraction, top to bottom. The shaded regions and areas enclosed between paired curves indicate 95% confidence intervals inferred from different combinations of observational probes, including the high-redshift galaxy UV luminosity functions (UF LFs), CMB optical depth (𝜏𝑒), neutra… view at source ↗
Figure 4
Figure 4. Figure 4: Left panel: Example of the 2D 21cm-galaxy cross-correlation S/N. The signal overlap region in k-space depends on galaxy survey redshift uncertainty and survey area, as well as SKA1-Low foreground assumptions (Yoshiura et al., 2018); Right panels: the S/N as a heatmap for the spherical 1D 21cm-galaxy cross-correlation PS for given survey specifications (y-axis) as a function of k (x-axis), assuming 1000 h S… view at source ↗
Figure 5
Figure 5. Figure 5: Cumulative SNR of 𝑧 ≃ 7 galaxy–21cm cross-power spectrum detection depending on FoV and depth, for slit spectroscopic (left column), grism (middle column), narrow-band (right column) galaxy surveys and two 21cm foreground scenarios, moderate (upper panels) and optimistic (lower panels), see also Gagnon-Hartman et al. (2025). emitters in Moriwaki et al. (2019). Finally, the cross-correlation, like the galax… view at source ↗
Figure 6
Figure 6. Figure 6: Left panel: The redshift evolution of the cross-power spectra between galaxies and fluctuations in the 21cm intensity (black solid), neutral fraction (blue dashed), gas temperature (orange dash-dotted), and matter density (green dotted) (Moriwaki et al., 2024); right panel: cross-correlation coefficient between galaxies and 21cm signal as a function of distance 𝑅 for different 𝑥HI values (Heneka and Mesing… view at source ↗
Figure 7
Figure 7. Figure 7: Left: 21cm differential brightness temperature distribution at 𝑧 = 7.1 and ⟨𝜒HI⟩ = 0.52 centering on an ionised regions with a size of 23.5 cMpc (Mishra et al., 2025). Right: Signal-to-noise ratio from matched filtering applied to 20 independent noise realizations of 200 hours SKA1-Low observations (Mishra et al., 2025). The shaded region indicates the 1𝜎 uncertainty from the realizations. Since the 21cm s… view at source ↗
Figure 8
Figure 8. Figure 8: Left: Stacked simulated 21cm images of ionised regions around galaxies at𝑧 = 9 for two foreground models from Davies et al. (2021): maximal contamination (𝑞 = 1) and a reduced case where foreground subtraction halves the horizon slope (𝑞 = 0.5). Top panels show the stacked 21cm signal in cylindrically average Fourier space, and the bottom panels show slices of the centre of the stacked profiles. Right: Sig… view at source ↗
Figure 9
Figure 9. Figure 9: Difference in the 21cm signal between regions with and without LAEs, averaged over 10 fields, as a function of an￾gular size for 1000 hours SKA observations (Hutter et al., 2017). Differences in the average 21cm differential bright￾ness temperatures between regions with and without Lyman-alpha emitting galaxies (LAEs) can constrain the IGM’s ionisation state and reionisation morphol￾ogy. Lyman-alpha radiat… view at source ↗
Figure 10
Figure 10. Figure 10: The southern sky from Declination −60 to the equator with overlaid galaxy surveys (white) and line intensity mapping surveys (yellow) which have already been carried out or will be carried out by 2030. The SKA-low FWHM is shown in orange for scale, with the right panel comparing the size of a proposed MOSAIC survey to pointings of the SKA-low and CCAT-prime (MOSAIC Mesinger et al. (2024); Gagnon-Hartman e… view at source ↗
read the original abstract

Synergies with other instruments will be essential in making, verifying, and interpreting a detection of the cosmic 21-cm signal from the Epoch of Reionization (EoR) and Cosmic Dawn (CD) with the Square Kilometer Array (SKA) telescope. Such synergies can (i) provide prior information about galaxies and the intergalactic medium (IGM) during the EoR/CD; (ii) pave the road to a first 21cm detection by mitigating foregrounds and systematics through cross-correlations; and (iii) give complimentary physical insights into the galaxy -- IGM connection. Here we review the current state of synergies and discuss what observations will best compliment SKA-low EoR/CD observations.

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. The manuscript is a review summarizing synergies between SKA-low 21-cm observations of the Epoch of Reionization (EoR) and Cosmic Dawn (CD) and other instruments. It claims that such synergies are essential for making, verifying, and interpreting a 21-cm detection, specifically by (i) supplying prior information on galaxies and the IGM, (ii) enabling a first detection via cross-correlation mitigation of foregrounds and systematics, and (iii) providing complementary insights into the galaxy-IGM connection. The paper reviews the current state of these synergies and identifies optimal complementary observations.

Significance. As a review that consolidates existing literature on multi-instrument approaches, the paper has value in framing the consensus need for external data to support SKA 21-cm science. It does not present new derivations or predictions but synthesizes how cross-correlations address foreground challenges, which can help guide observational planning if the cited works are represented faithfully.

minor comments (1)
  1. The abstract states that synergies 'pave the road to a first 21cm detection'; consider adding a brief forward reference in the introduction to the specific sections that review the cross-correlation literature supporting this point.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive review of our manuscript, their recognition of its value in consolidating the literature on multi-instrument synergies for SKA-low 21-cm observations, and their recommendation to accept.

Circularity Check

0 steps flagged

No significant circularity; review paper with no derivations

full rationale

This manuscript is a review summarizing the state of synergies for SKA-low 21-cm observations of the EoR/CD. It contains no original equations, predictions, fitted parameters, or derivation chains. The central claim—that external synergies are essential—is presented as a consensus framing supported by external literature, not as an internally derived result. No self-definitional steps, fitted inputs called predictions, or load-bearing self-citations appear. The paper is self-contained against external benchmarks and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is a review paper; no free parameters, axioms, or invented entities are introduced by the authors.

pith-pipeline@v0.9.1-grok · 5742 in / 994 out tokens · 37243 ms · 2026-07-01T00:55:44.059185+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

22 extracted references · 22 canonical work pages · 3 internal anchors

  1. [1]

    P.C.BreysseandM.Rahman.MonthlyNoticesoftheRoyalAstronomicalSociety,468(1):741–750, June 2017

    doi: 10.1093/mnras/stad3849. P.C.BreysseandM.Rahman.MonthlyNoticesoftheRoyalAstronomicalSociety,468(1):741–750, June 2017. doi: 10.1093/mnras/stx451. P. C. Breysse et al.The Astrophysical Journal, 933(2):188, July 2022. doi: 10.3847/1538-4357/ ac63c9. S. Bruton, Y.-H. Lin, C. Scarlata, and M. J. Hayes.The Astrophysical Journal Letters, 949(2):L40, 2023. C...

    work page doi:10.1093/mnras/stad3849 2017

  2. [2]

    doi: 10.1146/annurev-astro-082812-140953. B. Casavecchia, U. Maio, C. Péroux, and B. Ciardi.Astronomy & Astrophysics, 693:A119, Jan

    work page internal anchor Pith review doi:10.1146/annurev-astro-082812-140953

  3. [3]

    doi: 10.1051/0004-6361/202452282. M. Castellano et al.arXiv e-prints, art. arXiv:2504.05893, Apr. 2025. doi: 10.48550/arXiv.2504. 05893. CCAT-Prime Collaboration et al.The Astrophysical Journal Supplement Series, 264(1):7, Jan

    work page doi:10.1051/0004-6361/202452282 2025

  4. [4]

    doi: 10.3847/1538-4365/ac9838. A. Chakraborty and T. R. Choudhury.Journal of Cosmology and Astroparticle Physics, 2024(7): 078, July 2024. doi: 10.1088/1475-7516/2024/07/078. A. Chakraborty and T. R. Choudhury.arXiv e-prints, art. arXiv:2503.07590, Mar. 2025. doi: 10.48550/arXiv.2503.07590. T.-C. Chang et al.Bulletin of The AAS, 51(3):282, May 2019. doi: ...

    work page doi:10.3847/1538-4365/ac9838 2024

  5. [5]

    doi: 10.1086/324293. C. T. Donnan et al.Monthly Notices of the Royal Astronomical Society, 533(3):3222–3237, Sept

    work page doi:10.1086/324293

  6. [6]

    doi: 10.1093/mnras/stae2037. O. Doré et al.arXiv e-prints, art. arXiv:1412.4872, Dec. 2014. doi: 10.48550/arXiv.1412.4872. M. M. Dosibhatla et al.arXiv e-prints, art. arXiv:2508.09112, Aug. 2025. doi: 10.48550/arXiv. 2508.09112. S. Dumitru, G. Kulkarni, G. Lagache, and M. G. Haehnelt.Monthly Notices of the Royal Astro- nomical Society, 485(3):3486–3498, M...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stae2037 2014

  7. [7]

    doi: 10.1093/mnras/stu261. T. Fragos et al.The Astrophysical Journal, 764:41, Feb. 2013. doi: 10.1088/0004-637X/764/1/41. H. Fronenberg and A. Liu.The Astrophysical Journal, 975(2):222, Nov. 2024. doi: 10.3847/ 1538-4357/ad77cc. S.R.Furlanetto,A.Sokasian,andL.Hernquist.MonthlyNoticesoftheRoyalAstronomicalSociety, 347(1):187–195, Jan. 2004. doi: 10.1111/j....

    work page doi:10.1093/mnras/stu261 2013

  8. [8]

    doi: 10.1086/519835. T. Y.-Y. Hsiao et al.The Astrophysical Journal, 973(1):8, 2024. J. Hunacek et al.Journal of Low Temperature Physics, 193(5-6):893–900, Dec. 2018. doi: 10.1007/s10909-018-1906-3. A. Hutter, P. Dayal, V. Müller, and C. M. Trott.The Astrophysical Journal, 836(2):176, Feb. 2017. doi: 10.3847/1538-4357/836/2/176. A. Hutter, C. M. Trott, an...

    work page doi:10.1086/519835 2024

  9. [9]

    M.J.Jarvisetal.MonthlyNoticesoftheRoyalAstronomicalSociety,428(2):1281–1295,Jan.2013

    doi: 10.1093/mnras/sty1481. M.J.Jarvisetal.MonthlyNoticesoftheRoyalAstronomicalSociety,428(2):1281–1295,Jan.2013. doi: 10.1093/mnras/sts118. V. Jelić et al.Monthly Notices of the Royal Astronomical Society, 402(4):2279–2290, Mar. 2010. doi: 10.1111/j.1365-2966.2009.16086.x. X. Jin et al.The Astrophysical Journal, 942(2):59, 2023. G. C. Jones et al.Monthly...

    work page doi:10.1093/mnras/sty1481 2013

  10. [10]

    L.Liangetal.MonthlyNoticesoftheRoyalAstronomicalSociety,528(1):499–541,Feb.2024

    doi: 10.1088/1674-4527/16/8/132. L.Liangetal.MonthlyNoticesoftheRoyalAstronomicalSociety,528(1):499–541,Feb.2024. doi: 10.1093/mnras/stad3792. A.Lidzetal.TheAstrophysicalJournal,741(2):70,Nov.2011. doi: 10.1088/0004-637X/741/2/70. A. Liu and M. Tegmark.Physical Review D, 83(10):103006, May 2011. doi: 10.1103/PhysRevD. 83.103006. H. Liu and T. R. Slatyer.P...

    work page doi:10.1088/1674-4527/16/8/132 2024

  11. [11]

    doi: 10.3847/1538-4357/ad5ce8. R. Maiolino et al.Astronomy & Astrophysics, 691:A145, Nov. 2024. doi: 10.1051/0004-6361/ 202347640. B. Maity and T. R. Choudhury.Monthly Notices of the Royal Astronomical Society, 511(2): 2239–2258, Apr. 2022a. doi: 10.1093/mnras/stac182. B.MaityandT.R.Choudhury.MonthlyNoticesoftheRoyalAstronomicalSociety,515(1):617–630, Sep...

    work page doi:10.3847/1538-4357/ad5ce8 2024

  12. [12]

    doi: 10.1093/mnras/stac3304. S. Murray et al.The Journal of Open Source Software, 5(54):2582, Oct. 2020. doi: 10.21105/joss. 02582. M. Nakane et al.The Astrophysical Journal, 967(1):28, 2024. I.Nikolićetal.arXive-prints,art.arXiv:2501.07980,Jan.2025. doi: 10.48550/arXiv.2501.07980. C. D.Nunhokeeet al.TheAstrophysical Journal, 989(1):57, Aug.2025. doi: 10....

    work page doi:10.1093/mnras/stac3304 2020

  13. [13]

    doi: 10.1093/mnras/stad2411. M. Ouchi et al.Publications of the Astronomical Society of Japan, 70(SP1):S13, 2018. G. Paciga et al.Monthly Notices of the Royal Astronomical Society, 413(2):1174–1183, 04 2011. ISSN 0035-8711. doi: 10.1111/j.1365-2966.2011.18208.x. URLhttps://doi.org/10. 1111/j.1365-2966.2011.18208.x. H. Padmanabhan.Monthly Notices of the Ro...

    work page doi:10.1093/mnras/stad2411 2018

  14. [14]

    doi: 10.1093/mnras/stx3250. H. Padmanabhan and A. Loeb.arXiv e-prints, art. arXiv:2408.16820, Aug. 2024. doi: 10.48550/ arXiv.2408.16820. H.Padmanabhan,P.Breysse,A.Lidz,andE.R.Switzer.MonthlyNoticesoftheRoyalAstronomical Society, 515(4):5813–5822, Oct. 2022. doi: 10.1093/mnras/stac2025. S. Paul, S. Mukherjee, and T. R. Choudhury.Monthly Notices of the Roy...

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stx3250 2024

  15. [15]

    R.Salvaterra,B.Ciardi,A.Ferrara,andC.Baccigalupi.MonthlyNoticesoftheRoyalAstronomical Society, 360(3):1063–1068, July 2005

    doi: 10.48550/arXiv.2512.13943. R.Salvaterra,B.Ciardi,A.Ferrara,andC.Baccigalupi.MonthlyNoticesoftheRoyalAstronomical Society, 360(3):1063–1068, July 2005. doi: 10.1111/j.1365-2966.2005.09089.x. M. G. Santos, A. Cooray, and L. Knox.The Astrophysical Journal, 625(2):575–587, June 2005. doi: 10.1086/429857. N. S. Sartorio et al.Monthly Notices of the Royal ...

    work page doi:10.48550/arxiv.2512.13943 2005

  16. [16]

    doi: 10.1093/mnras/stad697. G. Sato-Polito, N. Kokron, and J. L. Bernal.Monthly Notices of the Royal Astronomical Society, 526(4):5883–5899, Dec. 2023. doi: 10.1093/mnras/stad2498. S.SazonovandR.Sunyaev.MonthlyNoticesoftheRoyalAstronomicalSociety,454(4):3464–3471, Dec. 2015. doi: 10.1093/mnras/stv2255. J. Schaye et al.Monthly Notices of the Royal Astronom...

    work page doi:10.1093/mnras/stad697 2023

  17. [17]

    doi: 10.1088/0004-637X/806/2/209. M. B. Silva et al.The Astrophysical Journal, 763(2):132, Feb. 2013. doi: 10.1088/0004-637X/ 763/2/132. C. Simmonds et al.Monthly Notices of the Royal Astronomical Society, 535(4):2998–3019, Dec

    work page doi:10.1088/0004-637x/806/2/209 2013

  18. [18]

    doi: 10.1093/mnras/stae2537. E. Sobacchi and A. Mesinger.Monthly Notices of the Royal Astronomical Society, 453(2):1843– 1854, 2015. E. Sobacchi, A. Mesinger, and B. Greig.Monthly Notices of the Royal Astronomical Society, 459 (3):2741–2750, July 2016. doi: 10.1093/mnras/stw811. B. Spina et al.Astronomy & Astrophysics, 688:L26, 2024. N. O. Stutzer et al.A...

    work page doi:10.1093/mnras/stae2537 2015

  19. [19]

    doi: 10.1093/mnras/staa183. M. Walther, J. Oñorbe, J. F. Hennawi, and Z. Lukić.The Astrophysical Journal, 872(1):13, 2019. J. R. Weaver et al.The Astrophysical Journal Supplement Series, 258(1):11, Jan. 2022. doi: 10.3847/1538-4365/ac3078. A.Weibeletal.MonthlyNoticesoftheRoyalAstronomicalSociety,533(2):1808–1838,Sept.2024. doi: 10.1093/mnras/stae1891. L.W...

    work page doi:10.1093/mnras/staa183 2019

  20. [20]

    doi: 10.1086/497160. J. Yang et al.The Astrophysical Journal, 904(1):26, 2020. S.Yangetal.TheAstrophysicalJournal,929(2):140,Apr.2022. doi: 10.3847/1538-4357/ac5d57. S. Yoshiura et al.Monthly Notices of the Royal Astronomical Society, 479(2):2767–2776, Sept

    work page doi:10.1086/497160 2020

  21. [21]

    doi: 10.1093/mnras/sty1472. S. Yoshiura et al.Monthly Notices of the Royal Astronomical Society, 483(2):2697–2711, Feb

    work page doi:10.1093/mnras/sty1472

  22. [22]

    S.Yoshiuraetal.MNRAS,000:1–15,2021

    doi: 10.1093/mnras/sty3248. S.Yoshiuraetal.MNRAS,000:1–15,2021. URLhttps://lambda.gsfc.nasa.gov/product/ foreground/fg_. B. Yue and A. Ferrara.Monthly Notices of the Royal Astronomical Society, 490(2):1928–1943, Dec. 2019. doi: 10.1093/mnras/stz2728. B. Yue et al.Monthly Notices of the Royal Astronomical Society, 450(4):3829–3839, July 2015. doi: 10.1093/...

    work page doi:10.1093/mnras/sty3248 2021