Constraining Cosmological Parameters with Galaxy Cluster Phase Spaces

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

In 1914, Einstein brought forth his foundations for General Relativity (GR) to explain gravity using the geometry of space and time. Einstein's GR ushered in the beginning of a new scientific paradigm shift for the science of the origin and evolution of the universe ("Cosmology"). This is now a golden age, similar to the centuries around Plato, Copernicus and Newton, and we are privileged to be witnesses to this paradigm shift in real-time. All scientific paradigms go through a long period of intense testing, as the data and the scientific methods push the theory to its limits. The Universe is so vast that there are physical scales on which GR should apply, but which have been difficult to test. Consider clusters of galaxies, which are the largest gravitationally bound objects in the Universe. Clusters entrap galaxies on scales of tens of millions of light years (i.e, 100 times larger than our own Milky Way). Does Einstein's GR still apply over such large distances in space-time? The escape velocity from a galaxy cluster is a combination of the local Newtonian gravitational potential and the acceleration of the expansion of the Universe. Weak lensing mass profiles of clusters can be used to predict the escape velocity profile from the gravitational Newtonian component and cosmology. This joint analysis provides a new direct avenue to constrain the dynamics of the expanding Universe and can simultaneously test GR and our standard Lambda CDM cosmological paradigm, time evolving dark energy, Chameleon gravity, and more. We will use the Michigan Magellan Fiber System (M2FS) to collect 100-200 galaxy cluster member spectra for escape velocities of clusters within the Dark Energy Survey (DES) footprint. We will directly compare the weak-lensing predicted escape velocity profiles to the observed profiles from the M2FS data in a likelihood analysis. Given a Hubble constant prior, this probe can achieve similar or better precision on the dark energy equation of state parameters compared to supernovae or the CMB. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.