The Baryonic Mass-Halo Mass Relation of Extragalactic Systems

TL;DR

This study establishes a comprehensive relation between baryonic mass and total mass in extragalactic systems, revealing how baryon fraction varies across different mass scales and aligning with cosmic values in massive clusters.

Contribution

It provides the first unified analysis covering nine orders of magnitude in baryonic mass, combining kinematic and gravitational lensing data to characterize the baryonic mass-halo mass relation.

Findings

Baryon fraction approaches cosmic value in massive clusters.

Baryon fraction decreases systematically with decreasing mass.

The relation is well described by a hyperbolic tangent function.

Abstract

We combine data for extragalactic systems to quantify a relation between the observed baryonic mass $M_b$ and the enclosed dynamical mass $M_{200}$ inferred from kinematics or gravitational lensing. Our sample covers nine orders of magnitude in baryonic mass, including galaxies with kinematic or weak gravitational lensing data and groups and clusters of galaxies with new gravitational lensing data. For rich clusters with $M_b > 10^{14}\;\mathrm{M}_{\odot}$, the observed baryon fraction is consistent with the cosmic value, $f_b = 0.157$. For lower masses, the baryon fraction decreases systematically with mass. The variation is well described by $M_b/M_{200} = f_b \tanh(M_b/M_0)^{1/4}$ with $M_0 \approx 5 \times 10^{13}\;\mathrm{M}_{\odot}$. This relation is qualitatively similar to stellar mass-halo mass relations derived from abundance matching, but exhibits less scatter.