# A UNIVERSAL MODEL FOR HALO CONCENTRATIONS

## Abstract

We present a numerical study of dark matter halo concentrations in ΛCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, ν, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, n, which affects both the normalization and shape of the c-ν relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed ν, halos at higher z experience steeper slopes n, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven-parameter function of only ν and n. This model matches our ΛCDM results to ≲ 5% accuracy up to z = 6, and matches scale-free Ω{sub m} = 1 models to ≲ 15%. The model also reproduces the low concentration values of Earth-mass halos at z ≈ 30, and thus correctly extrapolates over 16 orders of magnitude in halo mass. The predictions of our model differ significantly from all models previouslymore »

- Authors:

- Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637 (United States)

- Publication Date:

- OSTI Identifier:
- 22364429

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Astrophysical Journal; Journal Volume: 799; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CONCENTRATION RATIO; COSMOLOGICAL CONSTANT; COSMOLOGY; ENERGY SPECTRA; MASS; NONLUMINOUS MATTER; NUMERICAL ANALYSIS; RED SHIFT; STAR CLUSTERS; UNIVERSE

### Citation Formats

```
Diemer, Benedikt, and Kravtsov, Andrey V., E-mail: bdiemer@oddjob.uchicago.edu.
```*A UNIVERSAL MODEL FOR HALO CONCENTRATIONS*. United States: N. p., 2015.
Web. doi:10.1088/0004-637X/799/1/108.

```
Diemer, Benedikt, & Kravtsov, Andrey V., E-mail: bdiemer@oddjob.uchicago.edu.
```*A UNIVERSAL MODEL FOR HALO CONCENTRATIONS*. United States. doi:10.1088/0004-637X/799/1/108.

```
Diemer, Benedikt, and Kravtsov, Andrey V., E-mail: bdiemer@oddjob.uchicago.edu. Tue .
"A UNIVERSAL MODEL FOR HALO CONCENTRATIONS". United States.
doi:10.1088/0004-637X/799/1/108.
```

```
@article{osti_22364429,
```

title = {A UNIVERSAL MODEL FOR HALO CONCENTRATIONS},

author = {Diemer, Benedikt and Kravtsov, Andrey V., E-mail: bdiemer@oddjob.uchicago.edu},

abstractNote = {We present a numerical study of dark matter halo concentrations in ΛCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, ν, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, n, which affects both the normalization and shape of the c-ν relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed ν, halos at higher z experience steeper slopes n, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven-parameter function of only ν and n. This model matches our ΛCDM results to ≲ 5% accuracy up to z = 6, and matches scale-free Ω{sub m} = 1 models to ≲ 15%. The model also reproduces the low concentration values of Earth-mass halos at z ≈ 30, and thus correctly extrapolates over 16 orders of magnitude in halo mass. The predictions of our model differ significantly from all models previously proposed in the literature at high masses and redshifts. Our model is in excellent agreement with recent lensing measurements of cluster concentrations.},

doi = {10.1088/0004-637X/799/1/108},

journal = {Astrophysical Journal},

number = 1,

volume = 799,

place = {United States},

year = {Tue Jan 20 00:00:00 EST 2015},

month = {Tue Jan 20 00:00:00 EST 2015}

}