[Paper Review] New evidence for dark matter

Alexey Boyarsky, Oleg Ruchayskiy+3 more|ArXiv.org|Nov 10, 2009

Dark Matter and Cosmic Phenomena86 references20 citations

TL;DR

This paper presents a universal scaling relation between dark matter column density (𝒮) and halo mass (𝑀₂₀₀) across galaxies and galaxy clusters, demonstrating a tight power-law relationship that holds across 805 dark matter profiles spanning four orders of magnitude in radius and eight in mass. The observed 𝒮 ∝ 𝑀₂₀₀⁰.²¹ relation shows remarkable agreement with pure cold dark matter simulations, providing new, direct evidence for dark matter's existence independent of profile assumptions or baryonic feedback effects.

ABSTRACT

We present a new universal relation, satisfied by matter distributions at all observed scales, and show its amazingly good and detailed agreement with the predictions of the most up-to-date pure dark matter simulations of structure formation in the Universe. This work extends the previous analysis [0904.4054; 0909.5203] to a larger range of masses, demonstrates a different scaling law, and compares it with numerical simulations. This behaviour seems to be insensitive to the complicated feedback of baryons on dark matter. Therefore, it potentially allows to compare theoretical predictions directly with observations, thus providing a new tool to constrain the properties of dark matter. Such a universal property, observed in structures of all sizes (from dwarf spheroidal galaxies to galaxy clusters), is difficult to explain without dark matter, thus providing new evidence for its existence.

Motivation & Objective

• To identify a universal, profile-independent property of dark matter distributions across cosmic structures.
• To test whether observed dark matter column density 𝒮 scales universally with halo mass, independent of baryonic feedback or halo type.
• To provide a new observational constraint on dark matter properties by comparing with pure N-body simulations.
• To resolve ambiguity in cored vs. cusped dark matter profiles by introducing a robust, profile-insensitive observable.

Proposed method

• Defined a dark matter column density 𝒮 as the average surface density within radius 𝑟⋆, derived from 3D density profiles using cylindrical mass integration.
• Used a unified normalization of 𝑟⋆ across different profiles (NFW, ISO, BURK) so that 𝒮 becomes insensitive to profile type (differences <10%).
• Compiled a catalog of 805 dark matter profiles from 289 unique objects (dwarf spheroidals, spirals, ellipticals, galaxy groups, clusters), using data from 50+ publications.
• Fitted the observed 𝒮 vs. 𝑀₂₀₀ relation with a power law: log𝒮 = 0.21 log(𝑀₂₀₀/10¹⁰𝑀⊙) + 1.79.
• Validated the scaling relation across diverse systems, from dSphs to galaxy clusters, using consistent mass definition (𝑀₂₀₀).
• Compared the observed scaling with predictions from high-resolution pure dark matter simulations to confirm agreement.

Experimental results

Research questions

• RQ1 Is there a universal, profile-independent scaling relation between dark matter column density and halo mass across all cosmic structures?
• RQ2 To what extent does the observed scaling of 𝒮 with 𝑀₂₀₀ match predictions from pure cold dark matter simulations?
• RQ3 Can the observed scaling relation be explained without invoking baryonic feedback or alternative dark matter models?
• RQ4 Does the consistency of 𝒮 across different halo types and profiles provide new evidence for the existence of dark matter?

Key findings

• A universal scaling relation 𝒮 ∝ 𝑀₂₀₀⁰.²¹ is observed across 805 dark matter profiles spanning 0.2 kpc ≤ 𝑟⋆ ≤ 2.5 Mpc and 10⁸ 𝑀⊙ ≤ 𝑀₂₀₀ ≤ 10¹⁴ 𝑀⊙.
• The observed relation is in excellent agreement with predictions from pure cold dark matter simulations, with no significant deviation across scales.
• The dark matter column density 𝒮 is robust to profile choice: differences between NFW, ISO, and BURK profiles are less than 10% when 𝑟⋆ is normalized consistently.
• The relation holds across all halo types, including dwarf spheroidals, spiral galaxies, and galaxy clusters, indicating a fundamental property of dark matter halos.
• The observed scaling is insensitive to baryonic feedback, suggesting that the relation is a direct probe of dark matter physics.
• The tightness of the relation (R² ≈ 0.9) and its agreement with simulations provide strong, independent evidence for the existence of dark matter.