Abstract
AbstractIn this review, I discuss the use of galaxy-galaxy weak lensing measurements to study the masses of dark matter halos in which galaxies reside. After summarizing how weak gravitational lensing measurements can be interpreted in terms of halo mass, I review measurements that were used to derive the relationship between optical galaxy mass tracers, such as stellar mass or luminosity, and dark matter halo mass. Measurements of galaxy-galaxy lensing from the past decade have led to increasingly tight constraints on the connection between dark matter halo mass and optical mass tracers, including both the mean relationships between these quantities and the intrinsic scatter between them. I also review some of the factors that can complicate analysis, such as the choice of modeling procedure, and choices made when dividing up samples of lens galaxies.
Highlights
The field of galaxy formation and evolution seeks to explain the evolutionary history of galaxies, but is handicapped by the difficulties in observing the dark matter field in which the galaxies form and evolve
The purpose of this review is to describe some of the studies that have analyzed galaxygalaxy weak lensing measurements to learn about the masses of dark matter halos around galaxies, and to highlight important lessons learned and unsolved aspects of this problem that require more work in future, for example for the generation of large lensing surveys that will measure weak gravitational lensing more precisely than has been done with current datasets
Dividing M∗/Mhalo by the cosmological baryon fraction to estimate an efficiency of conversion of baryons to stars, η = M∗ Ωm Mhalo Ωb they found η ∼ 33% and ∼ 14%, respectively, for early and late type galaxies
Summary
The field of galaxy formation and evolution seeks to explain the evolutionary history of galaxies, but is handicapped by the difficulties in observing the dark matter field in which the galaxies form and evolve. The connection between galaxies and their host dark matter halos is an essential ingredient in the physics of galaxy formation. One very useful probe of the galaxy-dark matter connection is weak lensing around galaxies, or galaxy-galaxy lensing (e.g., Hoekstra & Jain 2008). Gravitational lensing, the deflection of light by mass, induces tangential shear distortions in the shapes of background galaxies around foreground galaxies, allowing direct measurement of the galaxy-matter correlation function. This approach has the advantage of being sensitive to all matter, independent of its dynamical state. The individual distortions are small (typically of order 0.1%), but by averaging over all foreground (“lens”) galaxies within a given subsample selected based on their properties (a process known as “stacking”), and over all the source galaxies behind them, it is possible to obtain a high signal-to-noise measurement of the shear as a function of angular separation from the galaxy, known as the galaxy-galaxy lensing signal
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