REVIEW
An excursion set model of hierarchical clustering: Ellipsoidal collapse and the moving barrier
Astrophysics · Submitted 7 May 2001 · 26 references
Pith's verdict: The analytic first-crossing formula is the real contribution and it holds up; the 'wide variety of barriers' line is two shapes and an ad hoc truncation, which the authors half-admit.
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Referee report
The paper
The paper claims
The paper argues that dark matter halo abundances and progenitor counts are better described by random walks crossing a barrier that rises with the smoothing scale than by the classical flat barrier of spherical collapse, and gives a closed
The reading
What carries the argument
The load-bearing object is the moving barrier $B(S,z)=sqrt{a},delta_{sc}(z)[1+beta(anu)^{-alpha}]$ with $nu equiv [delta_{sc}(z)/sigma(m)]^2$, together with the ansatz that the first-crossing distribution is the constant-barrier Gaussian form multiplied by a truncated Taylor series $T(S)=sum_{n=0}^{5}(-S)^n/n!,partial^n B/partial S^n$ of the barrier. The same substitution rule, $B(s)to B(s)-B(S)$ and $Sto s-S$, carries the formula over to the two-barrier problem that defines the conditional mass function, which is what makes progenitor counts and local-density mass functions accessible without a fresh numerical fit for every parent mass. Two auxiliary devices do real work: a sampling trick that turns a Gaussian variate $x$ into a mass via $anu=|x|^{3.6}/(1+|x|^{1.6})$, accurate to about a percent, and a six-dimensional random walk built from the deformation tensor, which is used to check that replacing the scatter in the shear field by its mean is a fair reduction.
Extended reading notes
Core claim
The central claim is that the first-crossing distribution of a Brownian walk absorbed on a moving barrier $B(S)$ is well approximated by $f(S)=|T(S)|e^{-B(S)^2/2S}/(Ssqrt{2pi S})$, where $T(S)$ is the sum of the first five terms of the Taylor expansion of $B(S)$ in $S$; the expression is exact for constant and linear barriers, where the series terminates, and remains accurate for the ellipsoidal barrier $B=sqrt{a},delta_{sc}(z)[1+beta(anu)^{-alpha}]$ with $beta approx 0.485$, $alpha approx 0.615$ and $a approx 0.7$. Feeding it the ellipsoidal barrier reproduces both the unconditional mass function and the conditional (progenitor) mass function measured in the GIF $N$-body simulations better than the constant-barrier spherical-collapse prediction, and the same machinery, with local density mapped to an effective redshift, gives the mass function inside dense and underdense cells. The authors are explicit that the improvement holds at large lookback times: at small lookback times, and for progenitors more than half the parent mass, the moving-barrier conditional mass function has the wrong shape, and they trace that to the excursion set neglect of correlations between smoothing scales rather than to the barrier shape itself.
Load-bearing premise
The premise everything rests on is that the collapse condition can be written as a barrier depending only on the smoothing scale, with the scatter a real patch feels from its surrounding shear field averaged away, and that the barrier's overall amplitude $a approx 0.7$ is legitimately fixed against the same simulations the resulting formula is then tested on.
Original abstract
The excursion set approach allows one to estimate the abundance and spatial distribution of virialized dark matter haloes efficiently and accurately. The predictions of this approach depend on how the nonlinear processes of collapse and virialization are modelled. We present simple analytic approximations which allow us to compare the excursion set predictions associated with spherical and ellipsoidal collapse. In particular, we present formulae for the universal unconditional mass function of bound objects and the conditional mass function which describes the mass function of the progenitors of haloes in a given mass range today. We show that the ellipsoidal collapse based moving barrier model provides a better description of what we measure in the numerical simulations than the spherical collapse based constant barrier model, although the agreement between model and simulations is better at large lookback times. Our results for the conditional mass function can be used to compute accurate approximations to the local-density mass function which quantifies the tendency for massive haloes to populate denser regions than less massive haloes. This happens because low density regions can be thought of as being collapsed haloes viewed at large lookback times, whereas high density regions are collapsed haloes viewed at small lookback times. Although we have only applied our analytic formulae to two simple barrier shapes, we show that they are, in fact, accurate for a wide variety of moving barriers. We suggest how they can be used to study the case in which the initial dark matter distribution is not completely cold.
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.
The abstract, sentence by sentence
The excursion set approach allows one to estimate the abundance and spatial distribution of virialized dark matter haloes efficiently and accurately. The predictions of this approach depend on how the nonlinear processes of collapse and virialization are modelled. We present simple analytic approximations which allow us to compare the excursion set predictions associated with spherical and ellipsoidal collapse. In particular, we present formulae for the universal unconditional mass function of bound objects and the conditional mass function which describes the mass function of the progenitors of haloes in a given mass range today. We show that the ellipsoidal collapse based moving barrier model provides a better description of what we measure in the numerical simulations than the spherical collapse based constant barrier model, although the agreement between model and simulations is better at large lookback times. Our results for the conditional mass function can be used to compute accurate approximations to the local-density mass function which quantifies the tendency for massive haloes to populate denser regions than less massive haloes. This happens because low density regions can be thought of as being collapsed haloes viewed at large lookback times, whereas high density regions are collapsed haloes viewed at small lookback times. Although we have only applied our analytic formulae to two simple barrier shapes, we show that they are, in fact, accurate for a wide variety of moving barriers. We suggest how they can be used to study the case in which the initial dark matter distribution is not completely cold.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The excursion set approach allows one to estimate the abundance and spatial distribution of virialized dark matter haloes efficiently and accurately. | background 1.00 | 0.10 | 0.04 | asserted 0.98 |
| s1 | The predictions of this approach depend on how the nonlinear processes of collapse and virialization are modelled. | background 0.99 | 0.06 | 0.02 | asserted 1.00 |
| s2 | We present simple analytic approximations which allow us to compare the excursion set predictions associated with spherical and ellipsoidal collapse. | contribution 0.88 | 0.95 | 0.06 | asserted 0.97 |
| s3 | In particular, we present formulae for the universal unconditional mass function of bound objects and the conditional mass function which describes the mass function of the progenitors of haloes in a given mass range today. | contribution 0.98 | 0.93 | 0.06 | asserted 0.99 |
| s4 | We show that the ellipsoidal collapse based moving barrier model provides a better description of what we measure in the numerical simulations than the spherical collapse based constant barrier model, although the agreement between model and simulations is better at large lookback times. | result 1.00 | 0.94 | 0.78 | asserted 1.00 |
| s5 | Our results for the conditional mass function can be used to compute accurate approximations to the local-density mass function which quantifies the tendency for massive haloes to populate denser regions than less massive haloes. | result 0.38 | 0.85 | 0.07 | asserted 0.54 |
| s6 | This happens because low density regions can be thought of as being collapsed haloes viewed at large lookback times, whereas high density regions are collapsed haloes viewed at small lookback times. | interpretation 1.00 | 0.29 | 0.04 | asserted 0.92 |
| s7 | Although we have only applied our analytic formulae to two simple barrier shapes, we show that they are, in fact, accurate for a wide variety of moving barriers. | result 0.82 | 0.94 | 0.10 | asserted 1.00 |
| s8 | We suggest how they can be used to study the case in which the initial dark matter distribution is not completely cold. | future work 1.00 | 0.49 | 0.04 | hedged possibility 0.97 |
What was examined, and what was not
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Figures
Showing 10 of the paper's 14 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:astro-ph/0105113 by the authors.
References
How later papers used it
233 later papers cite it
25 later papers by other authors are listed below: 25 used its method or tool.
Uses its method or tool 25 of 89 papers with this label
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Used a halo mass function conditioned on pixel overdensity following this paper to statistically sample unresolved low-mass halos.
Simulating the Large-Scale Structure of HI Intensity Maps (2015) · 1.00 · paraphrased: the licence does not allow quoting
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Computed the comoving halo mass function as a function of redshift and halo mass using the excursion set approach from another work accounting for ellipsoidal collapse from this paper.
Can primordial black holes explain the overabundance of bright super-early galaxies? (2025) · 1.00 · paraphrased: the licence does not allow quoting
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Followed this paper for the halo mass function and another work for the halo bias in its halo model approach.
Beyond $\Lambda$CDM with HI intensity mapping: robustness of cosmological constraints in the presence of astrophysics (2019) · 1.00 · paraphrased: the licence does not allow quoting
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Computed the halo mass function using the Sheth-Tormen multiplicity function.
Soliton Merger Rates and Enhanced Axion Dark Matter Decay (2023) · 1.00 · paraphrased: the licence does not allow quoting
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Utilized a sub-grid prescription based on this paper's conditional ellipsoidal mass function to compute the halo field.
A fast method of reionization parameter space exploration using GPR trained SCRIPT (2023) · 1.00 · paraphrased: the licence does not allow quoting
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Populated each grid cell with halos using a conditional ellipsoidal collapse model from this paper.
SCRIPT in the Cosmic Dawn: Distinguishing Redshift-Evolving Galaxy Populations with 21-cm Fluctuations (2026) · 1.00 · paraphrased: the licence does not allow quoting
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Applied this paper's conditional mass function to populate grid cells with halos above a minimum mass.
Unbiased constraints on reionization model parameters in presence of the foreground wedge (2018) · 1.00 · paraphrased: the licence does not allow quoting
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Computed the collapsed mass fraction in haloes using a subgrid prescription based on this paper's conditional ellipsoidal collapse model.
Probing the Physics of Reionization Using kSZ Power Spectrum from Current and Upcoming CMB Surveys (2023) · 1.00 · paraphrased: the licence does not allow quoting
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Computed the collapsed mass fraction in haloes using a subgrid prescription based on this paper's conditional ellipsoidal collapse model.
Disentangling patchy reionization signatures from primordial gravitational waves using CMB $E$-mode and $B$-mode polarization (2023) · 1.00 · paraphrased: the licence does not allow quoting
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We now elaborate on the computation of each of the components that goes into Eq.[ref]: (i) In our calculations, we use the Sheth-Tormen HMF [ref]
Constraints on the fuzzy dark matter mass window from high-redshift observables (2024) · UV luminosity functions · 1.00
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We obtain the HMF by using the classical [ref] formalism, which uses an ellipsoidal model for perturbation collapse[Throughout the paper, we assume a flat Universe with the following cosmological parameters: $Ω_M = 0.3075$, $Ω_Λ = 1- Ω_M$, and $Ω_b = 0.0486$, $h=0.6774$, $σ_8=0.826$, where $Ω_M$, $Ω_Λ$, and $Ω_b$ are the total matter, vacuum, and baryon densities, in units of the critical density; $h$ is the Hubble constant in units of $100$, and $σ_8$ is the late-time fluctuation amplitude parameter [ref] .].
On the stunning abundance of super-early, massive galaxies revealed by JWST (2022) · Building the luminosity function · 0.99
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A key connection between astrophysics and PMFs is encoded in the halo mass function $dn_h/dlnM$, which we compute from the matter power spectrum [ref] within the excursion-set formalism formalism [ref] with ellipsoidal collapse [ref] .
JWST Constraints on Primordial Magnetic Fields (2026) · Introduction · 0.99
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Started from this paper's Sheth-Tormen halo mass function and assumed each halo to contain a gas mass linked to halo mass through the cosmological baryon-to-dark matter ratio.
Are the Newly-Discovered $z \sim 13$ Drop-out Sources Starburst Galaxies or Quasars? (2022) · 0.99 · paraphrased: the licence does not allow quoting
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Used this paper's Sheth-Tormen mass function, as in another work but with a fit calibrated to high-redshift N-body simulations from another work.
Insights from HST into Ultra-Massive Galaxies and Early-Universe Cosmology (2023) · 0.92 · paraphrased: the licence does not allow quoting
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Adjusted this paper's mass function for finite volume effects by correcting the mass variance and shifting the collapse threshold by the subregion overdensity.
The halo mass function and inner structure of ETHOS haloes at high redshift (2021) · 0.92 · paraphrased: the licence does not allow quoting
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Generated dark matter halo mass functions as a function of redshift following this paper, then assigned stars to each halo.
Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionisation (2016) · 0.81 · paraphrased: the licence does not allow quoting
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Adopted this paper's Sheth-Tormen halo mass function model.
The Star Formation Efficiency During Reionization as Inferred from the Hubble Frontier Fields (2023) · 0.98 · paraphrased: the licence does not allow quoting
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Adapted the collapse formalism developed by Sheth and Tormen, giving a halo mass function with specified parameters.
First Constraints on Small-Scale Non-Gaussianity from UV Galaxy Luminosity Functions (2020) · 0.99 · paraphrased: the licence does not allow quoting
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Used this paper's Sheth-Tormen form of the comoving number density of dark matter haloes per unit logarithmic halo mass to estimate halo masses from Lyman-alpha luminosities.
Intergalactic Lyman-$\alpha$ haloes before reionization are detectable with JWST (2024) · 0.99 · paraphrased: the licence does not allow quoting
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Used the Sheth-Tormen mass function, which extends the Press-Schechter formalism to ellipsoidal collapse as in this paper.
Milky Way satellite velocities reveal the Dark Matter power spectrum at small scales (2023) · 0.96 · paraphrased: the licence does not allow quoting
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Used this paper's Sheth-Tormen approximation for the halo mass function following another work for all dark matter models.
Can EDGES observation favour any dark matter model? (2019) · 0.93 · paraphrased: the licence does not allow quoting
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Made use of the Sheth-Tormen mass function given by this paper.
New Roads to the Small-Scale Universe: Measurements of the Clustering of Matter with the High-Redshift UV Galaxy Luminosity Function (2021) · 0.99 · paraphrased: the licence does not allow quoting
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Used the Sheth-Tormen mass function given by this paper in its fiducial model.
GALLUMI: A Galaxy Luminosity Function Pipeline for Cosmology and Astrophysics (2021) · 0.97 · paraphrased: the licence does not allow quoting
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Used a semi-analytical prescription based on sampling a conditional mass function given by this paper's fitting form.
Photon number conservation and the large-scale 21 cm power spectrum in semi-numerical models of reionization (2018) · 0.93 · paraphrased: the licence does not allow quoting
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Regarding the halo mass function, we assume the [ref] prescription (Eq. [ref]) with modified parameter $q=0.85$.
A halo model approach for the 21-cm power spectrum at cosmic dawn (2020) · Results · 0.87
How the literature uses it
109 arXiv papers cite this in 172 sentences
Papers citing it · 92 sentences without a confident label
Uses its method or tool 45 papers
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Confronting JWST Massive Galaxies. — By assuming that each dark-matter halo at high $z$ contains a single central galaxy, the expected number of galaxies with stellar mass larger than some observational threshold $M_⋆^obs$ can be obtained as [ref] : [equation] where Vol $=Ω(r_max^3 - r_min^3)/3$ is the comoving survey volume, determined by the surveyed redshift range (from $r(z_min)$ to $r(z_max)$) and the survey angular coverage $Ω$, and $dn/dM_h$ is the halo mass function[We will use the Sheth-Tormen [ref] mass function as in Ref. [ref] , but with a fit calibrated to high-redshift N-body simulations from Ref. [ref] .].
Insights from HST into Ultra-Massive Galaxies and Early-Universe Cosmology · Introduction · 0.92
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To this purpose we use the Sheth & Tormen mass function [ref] dndM = -√(2ãπ)A ł[1+ł(ã δ_c^2D^2σ_M^2)̊^-p]̊ ρ_mM^2δ_cDσ_M × dlnσ_Mdln M expł(-ã δ_c^22D^2σ_M^2)̊ , where $ã=0.707$ [We changed the commonly adopted notation to avoid confusion with the scale factor $a$.], $p=0.3$, $A=0.2162$, $δ_c$ is the linear critical density contrast derived in Section [ref], $D=δ^L_m/δ^L_m(a=1)$ is the linear growth factor, and $σ_M$ is the variance of the linear matter power spectrum defined as [ref] σ_M^2 = 12π^2∫^∞_0 dk k^2W^2(kR) P^L(k) , where the window function is defined as W(kR) = 3sin(kR)-kRcos(kR)(kR)^3 , being $R$ the comoving radius enclosing the mass $M=4π3ρ_mR^3$.
Growth of non-linear structures and spherical collapse in the Galileon Ghost Condensate model · Mass function · 0.98
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Since our simulations do not resolve all the low mass halos that are expected to host HI, we have used the coarse density field in each pixel to statistically sample these halos using a halo mass function conditioned on the overdensity of the pixel following [ref] .
Simulating the Large-Scale Structure of HI Intensity Maps · Conclusions · 1.00
Uses its data or values 2 papers
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The bias terms are given as (for the Sheth-Tormen and Tinker mass functions respectively) [ref] [equation] where $a_2=-17/21$ and we list other constants below [equation] We re-emphasize that all these constants are fit to Newtonian, $Λ$CDM simulations.
Modelling the matter bispectrum at small scales in modified gravity · Details of the halo model spectra · 0.80
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The corresponding halo masses and number densities ($M_h, dn/dlnM_h$) are approximately ($7 ×10^10 , 7 ×10^-6 Mpc^-3$) at $z = 12$, ($2 ×10^11 , 4 ×10^-6 Mpc^-3$) at $z = 10$, and ($2 ×10^12 , 9 ×10^-7 Mpc^-3$) at $z = 7$ [ref] .
Grain-size evolution and rapid dust growth in high-redshift galaxies · Model parameters and fiducial setup · 0.85
Compares with it 9 papers
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Our main arguments for the validity of our approach are the good agreement of the resulting unconditional halo mass function (see Figure [ref]) and large scale bias (see Figures [ref] and [ref]) with the analytical results from [ref] .
Simulating the Large-Scale Structure of HI Intensity Maps · HI intensity maps · 0.97
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In Fig. [ref] we compare our HMFs calculated from $N$-body simulations with HMFs from the Sheth-Tormen (ST) semi-analytic formulae [ref] .[See [ref] for other semi-analytic fits to the mass function, which we found to work less well for models with massive neutrinos.] The ST fit is based on the fact that, as first pointed out by Press and Schechter [ref] , the HMF can be written as [equation] with $ν≡[δ_sc(z)/σ(M)]^2$, where $δ_sc(z)=1.686$ is the overdensity required for spherical collapse at $z$, and $ρ̅= Ω_m ρ_c$. $dn(M,z)$ is the number density of halos in the mass interval $M$ to $M + dM$.
Neutrinos in Non-linear Structure Formation - The Effect on Halo Properties · The halo mass function · 0.99
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Note that this expression matches the first two terms of [ref] which are equivalent to [ref] for $D_B=0$.
Spherical collapse and halo mass function in f(R) theories · Halo mass function prediction for uncorrelated random walk and generic barrier · 1.00
Cites it as support 1 paper
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However, [ref] showed that \(q_λ\) and \(δ_m\) encode complementary physical information and follow different distributions.
Astrophysical systematics in Kinematic Lensing: quantifying an Intrinsic Alignment analog · Characterizing the environment · 0.99
Cites it as background 14 papers
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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
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A large amount of research has been devoted to identifying mass functions that accurately describe the simulations and data of galactic halos, see, e.g., [ref] .
Toward More Realistic Mass Functions For Ultradense Dark Matter Halos · Introduction · 0.98
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Over the years, several layers of complexity have been added to the initial model, with the inclusion of the peak constraint [ref] , halos preferentially form at peaks in the initial field, the excursion set constraint to solve the cloud in cloud problem [ref] , and more realistic collapse models, halos are likely to form in a ellipsoidal fashion [ref] .
Weighing neutrinos with the halo environment · Analytical considerations on environmental bias · 0.84
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