Measuring the dark matter equation of state

TL;DR

This paper measures the dark matter equation of state using combined kinematic and lensing data, finding results consistent with pressureless dark matter and highlighting the need for a full relativistic approach.

Contribution

It applies an improved method to measure the dark matter equation of state, providing the first such measurement and testing it with simulations.

Findings

Dark matter equation of state is consistent with pressureless within errors

Lensing mass estimates tend to be larger than kinematic estimates

Results suggest the importance of a full relativistic analysis for dark matter

Abstract

The nature of the dominant component of galaxies and clusters remains unknown. While the astrophysics community supports the cold dark matter (CDM) paradigm as a clue factor in the current cosmological model, no direct CDM detections have been performed. Faber and Visser 2006 have suggested a simple method for measuring the dark matter equation of state that combines kinematic and gravitational lensing data to test the widely adopted assumption of pressureless dark matter. Following this formalism, we have measured the dark matter equation of state for first time using improved techniques. We have found that the value of the equation of state parameter is consistent with pressureless dark matter within the errors. Nevertheless, the measured value is lower than expected because typically the masses determined with lensing are larger than those obtained through kinematic methods. We have tested our techniques using simulations and we have also analyzed possible sources of error that could invalidate or mimic our results. In the light of this result, we can now suggest that the understanding of the nature of dark matter requires a complete general relativistic analysis.