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An analytic model for the spatial clustering of dark matter haloes

Astrophysics · Submitted 19 Dec 1995

Pith's verdict: The Eulerian halo bias formula is the real contribution and it holds up; the 'entirely analytic autocorrelation' line in the abstract is an empirical regularity the authors themselves flag as underived.

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arXiv IDastro-ph/9512127 (version 1)
Pith IDPDCFJZXS, Pith's permanent record of this paper and its review
CitationH. J. Mo, S. D. M. White. "An analytic model for the spatial clustering of dark matter haloes." arXiv:astro-ph/9512127 (1995). https://pith.science/paper/PDCFJZXS
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Referee report
The paper

The paper claims

Halo clustering can be computed from mass clustering times a single bias factor, and that factor comes from the Press-Schechter formalism plus spherical collapse.

The reading

The paper asks a narrow but consequential question: if galaxies live inside dark matter haloes, how does the spatial distribution of those haloes differ from the distribution of the mass? Mo and White answer with a model built from two ingredients that were already on the shelf — the extended Press-Schechter description of how much mass sits in collapsed objects on a given scale, and the spherical collapse of a density perturbation — and they get a bias function $b(M,R,z) = 1 + (1/6_c)(6_1^2-1)/6_1$ that says how much overdense in haloes a region of mass overdensity $6$ should be. The value of the result is that it turns halo clustering into arithmetic on the mass power spectrum: no simulation needed to ask where haloes of a given mass sit. They then check the model against large N-body simulations and find the bias relation and the halo–mass cross-correlation reproduced over a wide range of scales, halo masses, and identification epochs. The one place the formalism does not deliver is the halo autocorrelation, because haloes cannot overlap and the count variance inside a sphere is sub-Poisson; they show empirically that the standard two-point autocorrelation is nevertheless proportional to the mass autocorrelation, with the large-scale bias factor as the constant of proportionality, even where both are far above unity.

What carries the argument

The bias function $b(M,z_1) = 1 + (6_1^2-1)/6_1$, with $6_1 = 6_1/7_1$ the peak height of the halo's smoothing scale. Its two additive pieces have distinct origins: the $1$ comes from the spherical contraction (or expansion) of the region between Lagrangian and Eulerian space, and the $(6_1^2-1)/6_1$ term is the peak-background split bias imprinted on the initial Gaussian field, the same combination that appears in earlier high-peak arguments. The machinery that produces it is the conditional Press-Schechter mass fraction $f(7_1,6_1|7_0,6_0)$ of Bond et al., which gives the mean number of $M_1$ haloes inside a sphere of radius $R_0$ and overdensity $6_0$, plus the spherical-collapse relations $R/R_0 = (3/10)(1-6_0)^{-1}$ and the interpolating formula $6_0(6)$ used to invert them. The paper also defines an averaged cross-correlation $7_{hm}$ over spheres of fixed radius and overdensity, which depends only on the mean halo count and so sidesteps the scatter problem that blocks the autocorrelation.

Extended reading notes

Core claim

The central claim is that the bias of dark haloes relative to the mass is computable analytically and is accurate. Halos of mass $M$ identified at redshift $z_1$ are defined, following Press-Schechter, as regions whose linearly extrapolated overdensity exceeds $6_1 = (1+z_1)6_c$; the fraction of the mass in a larger sphere of linear overdensity $6_0$ that sits in such haloes follows from the conditional probability of Bond et al. (1991). Combining that with a spherical-collapse map from Lagrangian $(R_0,6_0)$ to Eulerian $(R,6)$ gives a mean halo overdensity $6_h = b(M,z_1)6$ with $b = 1 + (6_1^2-1)/6_1$, where $6_1 = 6_1/7_1$ is the peak height. Halos with $6_1=1$, i.e. mass $M_*$, are predicted unbiased; more massive haloes are positively biased and rarer, and low-mass haloes are mildly antibiased. The authors verify this bias function, the Lagrangian cross-correlation, and the Eulerian halo–mass cross-correlation against P$^3$M simulations with $N=10^6$ particles and several power-law spectra, finding agreement well into the nonlinear regime. They are explicit that the average autocorrelation cannot be obtained this way, because halo exclusion makes count variances substantially sub-Poisson; instead they measure the standard two-point halo autocorrelation and find it proportional to the mass autocorrelation with the large-scale bias factor squared, which is what licenses an entirely analytic estimate of halo clustering.

Load-bearing premise

The claim that halo clustering can be estimated entirely analytically rests on the empirical finding that the ratio of halo to mass autocorrelation equals the large-scale bias factor squared even on nonlinear scales; the paper itself notes that the formalism does not directly produce a model for the halo autocorrelation, so this proportionality is read off the simulations rather than derived.

Editorial extensions

If this is right

  • Halo clustering of any mass at any identification redshift can be predicted from the linear power spectrum alone, replacing a simulation with a formula for the bias factor.
  • The same bias factor applied to a known nonlinear mass correlation function (e.g. the fitting formula of Jain, Mo & White) yields the halo autocorrelation analytically, including on scales where the mass correlation is well above unity.
  • Because bias rises with identification redshift at fixed mass, galaxies formed at the centres of early low-mass haloes can be as strongly clustered today as much more massive haloes formed later, so a luminosity dependence of clustering is not a required feature of hierarchical models.
  • Expanding $6_h(6)$ to second order gives a calculable curvature $B_2$ in the bias relation, which feeds through to a predicted reduction in the skewness of halo counts relative to mass counts, potentially explaining the lower skewness measured for late-type galaxies.
  • If the abundance of a class of haloes is known, the peak height $6_1$ can be inferred, the mass correlation function recovered from the observed halo correlation function, and $7_8$ extracted as a function of the assumed density parameter $\Omega_0$ — which is how the method is proposed as a measurement of $\Omega$.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The proportionality $7_{hh} = b^2 7_m$ is the paper's most reusable export and its least derived one: it would be worth checking whether the ratio drifts with halo mass at fixed scale in simulations with larger boxes and better mass resolution than the ones available here.
  • If $7_{hh}/7_m$ really is scale-independent down to the exclusion scale, then the shape of the galaxy correlation function carries almost no information about halo occupation — only its amplitude does — which would sharpen the degeneracy between $7_8$ and $\Omega_0$ in exactly the direction the authors want to exploit.
  • The sub-Poisson count variance is treated as an obstacle; it could instead be treated as a signal, since the size of the deficit below Poisson measures the volume filling fraction of the excluded haloes and hence constrains their density profile.
  • The double-epoch construction — haloes identified at $a_1$, positions followed to $a_2$ — is a template for any abundance-matching scheme in which a galaxy keeps the identity of the halo it formed in even after that halo has merged.
Original abstract

We develop a simple analytic model for the gravitational clustering of dark matter haloes to understand how their spatial distribution is biased relative to that of the mass. The statistical distribution of dark haloes within the initial density field (assumed Gaussian) is determined by an extension of the Press-Schechter formalism. Modifications of this distribution caused by gravitationally induced motions are treated using a spherical collapse approximation. We test this model against results from a variety of N-body simulations, and find that it gives an accurate description of a bias function. This bias function is sufficient to calculate the cross-correlation between dark haloes and mass, and again we find excellent agreement between simulation results and analytic predictions. Because haloes are spatially exclusive, the variance in the count of objects within spheres of fixed radius and overdensity is significantly smaller than the Poisson value. This seriously complicates any analytic calculation of the autocorrelation function of dark halos. Our simulation results show that this autocorrelation function is proportional to that of the mass over a wide range in $R$, even including scales where both functions are significantly greater than unity. The constant of proportionality is very close to that predicted on large scales by the analytic model. This result permits an entirely analytic estimate of the autocorrelation function of dark haloes. We use our model to study how the distribution of galaxies may be biased with respect to that of the mass. In conjunction with other data these techniques should make it possible to measure the amplitude of cosmic mass fluctuations and the density of the Universe.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 8,800 input tokens, $0.0004 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.57 · human participants 0.01 · controlled comparison 0.09 · randomized assignment 0.01 · states quantitative result 0.25 · compares with prior results 0.86 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

We develop a simple analytic model for the gravitational clustering of dark matter haloes to understand how their spatial distribution is biased relative to that of the mass. The statistical distribution of dark haloes within the initial density field (assumed Gaussian) is determined by an extension of the Press-Schechter formalism. Modifications of this distribution caused by gravitationally induced motions are treated using a spherical collapse approximation. We test this model against results from a variety of N-body simulations, and find that it gives an accurate description of a bias function. This bias function is sufficient to calculate the cross-correlation between dark haloes and mass, and again we find excellent agreement between simulation results and analytic predictions. Because haloes are spatially exclusive, the variance in the count of objects within spheres of fixed radius and overdensity is significantly smaller than the Poisson value. This seriously complicates any analytic calculation of the autocorrelation function of dark halos. Our simulation results show that this autocorrelation function is proportional to that of the mass over a wide range in $R$, even including scales where both functions are significantly greater than unity. The constant of proportionality is very close to that predicted on large scales by the analytic model. This result permits an entirely analytic estimate of the autocorrelation function of dark haloes. We use our model to study how the distribution of galaxies may be biased with respect to that of the mass. In conjunction with other data these techniques should make it possible to measure the amplitude of cosmic mass fluctuations and the density of the Universe.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We develop a simple analytic model for the gravitational clustering of dark matter haloes to understand how their spatial distribution is biased relative to that of the mass. contribution 0.99 0.95 0.07 asserted 0.91
s1 The statistical distribution of dark haloes within the initial density field (assumed Gaussian) is determined by an extension of the Press-Schechter formalism. method 0.95 0.66 0.03 asserted 1.00
s2 Modifications of this distribution caused by gravitationally induced motions are treated using a spherical collapse approximation. method 0.99 0.77 0.03 asserted 0.98
s3 We test this model against results from a variety of N-body simulations, and find that it gives an accurate description of a bias function. result 0.86 0.96 0.25 asserted 1.00
s4 This bias function is sufficient to calculate the cross-correlation between dark haloes and mass, and again we find excellent agreement between simulation results and analytic predictions. result 1.00 0.96 0.15 asserted 1.00
s5 Because haloes are spatially exclusive, the variance in the count of objects within spheres of fixed radius and overdensity is significantly smaller than the Poisson value. result 0.71 0.58 0.06 asserted 1.00
s6 This seriously complicates any analytic calculation of the autocorrelation function of dark halos. background 0.44 0.23 0.03 asserted 0.98
s7 Our simulation results show that this autocorrelation function is proportional to that of the mass over a wide range in $R$, even including scales where both functions are significantly greater than unity. result 1.00 0.94 0.25 asserted 1.00
s8 The constant of proportionality is very close to that predicted on large scales by the analytic model. result 0.98 0.88 0.13 asserted 1.00
s9 This result permits an entirely analytic estimate of the autocorrelation function of dark haloes. interpretation 0.81 0.81 0.27 asserted 0.72
s10 We use our model to study how the distribution of galaxies may be biased with respect to that of the mass. contribution 0.75 0.90 0.06 hedged possibility 0.77
s11 In conjunction with other data these techniques should make it possible to measure the amplitude of cosmic mass fluctuations and the density of the Universe. future work 0.68 0.09 0.09 hedged possibility 1.00

What kind of paper the classifier reports this is: theoretical result 0.99 · evidence from simulation or computation 0.86.

What was examined, and what was not

sources read
  • arXiv listing abstract v1
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. The average cross-correlation function between haloes and mass in Lagrangian space, normalized by the linear average mass correlation function. Results from simulations are shown for haloes with mass M  32 (triangles), 64 (three-pointed stars), 128 (squares), and 256 (crosses). The solid curves are the model predictions. The statistics for the M > 256 samples in the simulations are poor, because they contain only small number of haloes. The power index n and the expansion factor a are shown in each panel
Figure 4. shows the ratio of the average cross-correlation between haloes and mass to the average autocorrelation of the mass. The heavy ticks on the horizontal axis show the values of R where  m = 1. Open symbols give results for haloes in various mass ranges as identi ed by the FOF group nder. Filled dots in Figure 4a give corresponding results for the SO group nder. We see clearly that the two group nders give similar results for the average cross-correlation function  hm. For the case n = 1:5, the SO haloes have slightly higher  hm than the corresponding FOF haloes because the SO

Showing 2 of the paper's 4 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:astro-ph/9512127 by the authors.

References
How later papers used it

243 later papers cite it

Evidence: substantial. 232 of the citing papers share no author with it, and 40 of those carry a confident label from Pith's citation classifier.

Pith read 40 of the 324 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Builds on it 1 paper
  • Generalized this paper's standard formula for the time evolution of linear bias to the case where merging is important.

    Gravity and Large-Scale Non-local Bias (2012) · 1.00 · paraphrased: the licence does not allow quoting

Uses its method or tool 15 of 28 papers with this label · 1 by the same authors

By the same authors

Uses its data or values 1 paper
  • Used the fitting function in this paper to convert a density contrast of 0.8 to a linearly extrapolated density contrast of -2.81.

    Voids as a Precision Probe of Dark Energy (2010) · 0.88 · paraphrased: the licence does not allow quoting

Compares with it 1 of 10 papers with this label
How the literature uses it

108 arXiv papers cite this in 150 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 94 sentences without a confident label

Builds on it 1 paper
  • Along the way, we generalized the standard formula of the time evolution of linear bias [ref] to the case where merging is important (see Eq. [ref]).

    Gravity and Large-Scale Non-local Bias · Conclusions · 1.00

Uses its method or tool 17 papers
Uses its data or values 1 paper
  • In order to estimate the number of voids of a particular size at a particular redshift, we use the Press-Schechter formalism to determine the number density of voids in a redshift bin centered at $z,$ with Eulerian comoving radius between $R_E$ and $R_E + d R_E.$ Simulations indicate that the number density of voids peaks at a density contrast of $δ≈-0.85$ [ref] , we shall consider all the voids to have a density contrast of 0.8, which can be seen to correspond to a linearly extrapolated density contrast of -2.81 using the fitting function in [ref] .

    Voids as a Precision Probe of Dark Energy · Estimate of Voids to be found from a survey · 0.88

Compares with it 5 papers
  • In particular, we compare against the fitting formulae from: * the predictions of spherical collapse [ref] : [equation] * the fit from [ref] (hereafter SMT01), motivated by the ellipsoidal collapse model and calibrated using simulations: [equation] with $a=0.707,b=0.5,c=0.6$. * the fit in [ref] (hereafter T10, see also Ref. [ref] ), also calibrated against simulations, with a more flexible form: [equation] where the parameters ($A,B,C,a,b,c$) are dependent on the virial overdensity, $Δ$, with respect to the mean density of the Universe, as detailed in Table 2 of T10.

    An Improved Fit for Linear Halo Bias at High Redshift · Comparison to existing fits · 1.00

  • In other words, references [ref] and [ref] derive an effect on the halo/galaxy bias that, for the local model, can be shown to be equivalent, at large scales, to the one described by Eq. ([ref]), and they actually coincide if one considers as well the high-peak limit $ν/σ_R≫1$ since, in this case [b_h,1-1]δ_c≃b_2σ_R^2≃ν^2=δ_c^2/σ_R^2, once one assumes an expression such as the one derived by [ref] for the galaxy quadratic bias parameter.

    Constraining Running Non-Gaussianity · Halo bias and primordial non-Gaussianity · 0.92

  • This differs from the more general Press-Schechter expression, $b_0,L=(ν^2-1)/δ_c$ [ref] , only by the term $-1/δ_c$, which is negligible for the massive halos considered here.

    Tracing Primordial Gravitational Waves via non-Gaussian Signatures of Halo Bias · Halo Bias Correction · 0.98

Cites it as background 30 papers
  • The theoretical framework underlying such clustering analysis, based on the Press-Schechter theory and cosmological $N$-body simulations, have shown that galaxies are biased tracers of the dark matter distribution, with their properties determined by the halos in which they form [ref] .

    ODIN: Clustering Properties of Ly$\alpha$ Blobs at $z$ $\sim$ 2.4 and 3.1 · Introduction · 0.93

  • In this perspective, the two main approaches are the excursion-set formalism [ref] and the theory of Lagrangian density peaks [ref] , which have been widely explored to provide theoretical models for the dark matter (DM) halo mass function (HMF), bias, halo correlation functions [ref] , and cosmic void size functions (VSF) [ref] , hereafter , [ref] .

    The universal multiplicity function: counting halos and voids · Introduction · 0.94

  • The excursion set formalism predicts the abundance of objects crossing a critical density threshold as a consequence of hierarchical structure formation in an initially linear Gaussian field [ref] .

    VERSUS: An excursion-set-inspired void-finder for the Stage-IV era · Voids in the matter field · 0.95

Discussion

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