Globular Cluster Systems and X-Ray Atmospheres in Galaxies

TL;DR

This study investigates the relationships between globular cluster systems, hot X-ray atmospheres, and total halo mass in massive early-type galaxies, revealing consistent scaling relations and a uniform dark matter fraction within 5 effective radii.

Contribution

It provides empirical scaling relations linking globular cluster mass, X-ray gas mass, and halo mass in high-mass early-type galaxies, supporting minimal feedback effects on globular cluster formation.

Findings

M_X scales linearly with halo mass (M_h)

Both M_GCS and M_X scale steeply with M_h

Dark matter fraction within 5 r_e is approximately 83%

Abstract

We compare the empirical relationships between the mass of a galaxy's globular system M_GCS, the gas mass in the hot X-ray atmosphere M_X within a fiducial radius of 5 r_e, the total gravitational mass M_grav within 5 r_e, and lastly the total halo mass M_h calibrated from weak lensing. We use a sample of 45 early-type galaxies (ETGs) for which both GCS and X-ray data are available; all the galaxies in our sample are relatively high-mass ones with M_h > 10^12 M_sun. We find that M_X ~ M_h^1.0, similar to the previously known scaling relation M_GCS ~ M_h^1.0. Both components scale much more steeply than the more well known dependence of total stellar mass M_star ~ M_h^0.3 for luminous galaxies. These results strengthen previous suggestions that feedback had little effect on formation of the globular cluster system. The current data are also used to measure the relative mass fractions of baryonic matter and dark matter (DM) within 5 r_e. We find a strikingly uniform mean of <f_DM> = 0.83 with few outliers and an rms scatter of +-0.07. This result is in good agreement with two recent suites of hydrodynamic galaxy formation models.