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arxiv: 2501.04960 · v4 · submitted 2025-01-09 · 🌌 astro-ph.CO

Influence of photometric galaxies redshift distribution in BAO estimation

Paula S. Ferreira , Ribamar R. R. Reis This is my paper

Pith reviewed 2026-05-23 06:02 UTC · model grok-4.3

classification 🌌 astro-ph.CO
keywords BAOphotometric redshiftsredshift PDFDES Y3photo-z estimatorscorrelation functioncosmological parameters
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The pith

The shape of the galaxy redshift PDF can shift the BAO feature position whether the PDF is included in the model or not.

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

The paper incorporates realistic redshift probability distribution functions from photometric galaxies in the DES Y3 LRG catalog into the cosmological model for the two-point correlation function. Four photo-z estimators are tested, each with two PDF shape selections, and the shift parameter alpha is estimated for selected cases to compare against the fiducial Planck model. The analysis finds that PDF shape affects the BAO position and that estimator performance varies, with a recommendation to use multiple algorithms in future surveys to assess systematics on parameters including the dark energy equation of state.

Core claim

For compatible z_eff, the shape of the galaxy redshift PDF could shift the BAO feature position either by including the PDF in the model or not, with the ANNz2 Gaussian sample selection yielding results closer to the fiducial Planck 18 Lambda CDM model while DNF performs best when the dark energy equation of state w0 is varied provided sufficient statistical data is available.

What carries the argument

The kernel window function f(z|zp) constructed from the matched spectroscopic sample, which provides the PDF selection probability when photometric redshift is close to spectroscopic redshift and is used to compute the transverse correlation function xi_perp(zp) via CAMB.

If this is right

  • The BAO feature position can shift depending on whether the realistic galaxy redshift PDF is included in the model.
  • ANNz2 with its respective sample selections outperforms the other estimators for most parameters examined.
  • DNF emerges as the optimal algorithm when the dark energy equation of state w0 is considered, provided there is sufficient statistical data.
  • Upcoming photo-z survey collaborations should incorporate multiple photo-z estimation algorithms in their cosmological inference process to understand systematic effects.

Where Pith is reading between the lines

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

  • Photo-z uncertainty modeling may need to become a standard marginalization step in BAO analyses of photometric data to avoid shifts in inferred parameters.
  • Applying the same PDF-inclusion test to simulated catalogs with known true redshifts could measure the typical magnitude of any BAO scale bias.
  • The observed estimator dependence suggests that cross-checks across multiple algorithms could improve robustness for other large-scale structure statistics beyond BAO.

Load-bearing premise

The kernel window function f(z|zp) from the matched spectroscopic sample accurately captures the selection probability for the photometric galaxies when their photo-z is close to the true redshift.

What would settle it

A measurement in which the BAO scale parameter alpha shows no shift when the same data is analyzed with different PDF shapes or different photo-z estimators at fixed z_eff would falsify the central claim.

read the original abstract

In the present study, we use the DES Y3 catalog of LRG to incorporate the realistic galaxies' redshift Probability Distribution Function(PDF) into the correlation function cosmological model. We used four different photo-z estimators ANNz2, BPZ, ENF, and DNF to compare how they affect the BAO feature constraint. Moreover, each algorithm included two sample selections based on distinct PDF shapes; one where the PDFs are nearly Gaussian and another opting for the least noisy PDFs with a pronounced peak. Following a parametrised model, we estimated the shift parameter $\alpha$ for the ANNz2 three cuts and the DNF full samples. We found that the BAO from ANNz2 Gaussian sample selection is closer to the fiducial Planck 18 $\Lambda$CDM model. Later, we computed the correlation function $\xi_perp(z_p)$ by getting the bin pairs transversal to each other using CAMB. The kernel window function is the $f(z|z_p)$ which is the selection of the PDF value when the photometric redshift is nearly the same as the spectroscopic redshift estimated by the matched spectroscopic sample. For compatible z eff, we concluded that the shape of the galaxy redshift PDF could shift the BAO feature position either by including the PDF in the model or not. We also learnt that, given the same spectroscopic sample, ANNz2 estimator with its respective selection samples outperforms other estimators for most parameters examined. When the dark energy equation of state parameter, $w_0$, is considered, DNF emerges as the optimal algorithm, provided it has sufficient statistical data. Our analysis recommends that upcoming photo-z survey collaborations incorporate multiple photo-z estimation algorithms in their cosmological inference process; this approach will facilitate comprehension of systematic effects on various parameters.

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

3 major / 2 minor

Summary. The manuscript examines how the shape of photometric galaxy redshift PDFs from different estimators (ANNz2, BPZ, ENF, DNF) affects BAO scale estimation in the DES Y3 LRG sample. It selects subsamples based on PDF shapes (Gaussian vs. peaked), estimates the shift parameter alpha for ANNz2 and DNF, computes the transverse correlation function xi_perp(zp) using a kernel f(z|zp) derived from matched spectroscopic data, and concludes that PDF shape can shift the BAO feature position, with ANNz2 performing well and recommending multiple estimators for future surveys.

Significance. If substantiated with proper error analysis and kernel validation, the result would be significant for cosmological analyses relying on photometric redshifts, as it suggests that PDF modeling choices can introduce biases in BAO measurements at a level relevant for precision cosmology. It provides a practical recommendation for survey collaborations to use multiple photo-z algorithms.

major comments (3)
  1. [Abstract] Abstract: The estimated alpha values for ANNz2 three cuts and DNF full samples are reported without associated uncertainties, covariance matrices, sample sizes after cuts, or statistical significance tests, preventing assessment of whether observed differences (e.g., ANNz2 Gaussian closer to Planck fiducial) are meaningful.
  2. [Abstract] Abstract (kernel window function paragraph): The kernel f(z|zp) is constructed solely from the matched spectroscopic subsample with no quantitative test or tolerance provided to verify that it accurately captures the selection probability for the full photometric LRG catalog when zp ≈ z; this assumption is load-bearing for attributing any xi_perp(zp) shift to PDF shape rather than selection mismatch.
  3. [Abstract] CAMB computation of xi_perp(zp): No details are given on the exact incorporation of the PDF into the model, the definition of z_eff compatibility, or how the window function is normalized, rendering the central claim that PDF shape shifts the BAO feature (with or without inclusion in the model) non-reproducible from the provided information.
minor comments (2)
  1. [Abstract] Abstract: The phrase 'ANNz2 three cuts' is used without defining the cuts or their relation to the two PDF-shape selections (Gaussian vs. pronounced peak).
  2. [Abstract] Abstract: The statement on DNF emerging as optimal for w0 'provided it has sufficient statistical data' lacks any quantitative threshold or comparison metric.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the careful review and constructive comments on our manuscript. We address each major comment below, agreeing that additional details are needed for clarity and reproducibility. Revisions will be made to the abstract and methods sections accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The estimated alpha values for ANNz2 three cuts and DNF full samples are reported without associated uncertainties, covariance matrices, sample sizes after cuts, or statistical significance tests, preventing assessment of whether observed differences (e.g., ANNz2 Gaussian closer to Planck fiducial) are meaningful.

    Authors: We agree that the abstract omits these statistical details, which are necessary for proper evaluation. The full manuscript contains the covariance matrices from the correlation function measurements and the underlying sample sizes. In the revised version we will update the abstract to report the alpha uncertainties, post-cut sample sizes, and a note on statistical significance of the differences relative to the Planck fiducial value. revision: yes

  2. Referee: [Abstract] Abstract (kernel window function paragraph): The kernel f(z|zp) is constructed solely from the matched spectroscopic subsample with no quantitative test or tolerance provided to verify that it accurately captures the selection probability for the full photometric LRG catalog when zp ≈ z; this assumption is load-bearing for attributing any xi_perp(zp) shift to PDF shape rather than selection mismatch.

    Authors: The kernel is derived exclusively from the matched spectroscopic subsample as stated. We acknowledge that no quantitative validation (e.g., tolerance on selection probability or representativeness test) is provided in the current text. In the revision we will add a dedicated paragraph in the methods section describing any available checks on the matched sample's representativeness for the full LRG catalog and, if such checks prove insufficient, explicitly state the assumption and its potential impact on the results. revision: yes

  3. Referee: [Abstract] CAMB computation of xi_perp(zp): No details are given on the exact incorporation of the PDF into the model, the definition of z_eff compatibility, or how the window function is normalized, rendering the central claim that PDF shape shifts the BAO feature (with or without inclusion in the model) non-reproducible from the provided information.

    Authors: The abstract is intentionally concise and therefore omits the technical implementation details. The full manuscript describes the PDF incorporation into the CAMB model, the z_eff definition, and window-function normalization. We will revise the abstract to include a brief reference to these procedures and ensure the methods section provides sufficient equations and steps for reproducibility; a short clarifying sentence will also be added to the abstract where space permits. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation compares data-driven α shifts to external Planck fiducial

full rationale

The paper estimates α from DES Y3 LRG photometric samples using four photo-z estimators and two PDF-shape selections, then compares results to the external Planck 2018 ΛCDM fiducial. The kernel f(z|zp) is built from a matched spectroscopic subsample and inserted into the CAMB computation of ξ_perp(zp); this is an explicit modeling input, not a self-definition or a fitted quantity renamed as a prediction. No equation reduces the reported PDF-shape shift in BAO position to a parameter fit by construction, and no load-bearing premise rests on a self-citation chain. The central claim remains an empirical comparison against an independent benchmark.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that the photo-z PDFs and the matched spectroscopic kernel accurately represent the true redshift distribution; no free parameters are explicitly fitted beyond the BAO scale alpha, and no new entities are introduced.

free parameters (1)
  • alpha
    BAO scale shift parameter estimated from the correlation function for selected samples.
axioms (1)
  • domain assumption The kernel window function f(z|zp) derived from the matched spectroscopic sample correctly describes the probability that a photometric galaxy at zp has true redshift z.
    Invoked when computing xi_perp(zp) with CAMB and when concluding that PDF shape shifts the BAO feature.

pith-pipeline@v0.9.0 · 5851 in / 1470 out tokens · 61911 ms · 2026-05-23T06:02:29.811883+00:00 · methodology

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Reference graph

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