My Ph.D
The main research aim of my Ph.D thesis to measure the interaction cross section of dark matter using the statically averaged offset between mass components of in-falling substructure in to massive galaxy clusters.
It is predicted that in-falling sub-halos should experience the same behaviour as the bullet cluster and separate their associated dark matter and gas halos. Using the galaxy group members as a proxy for the direction of in-fall we should be able to make a robust measurement of the scattering cross-section of dark matter.
Gravitational Lensing
In order to determine the distribution of dark matter in galaxy clusters, we use the deformation of background source galaxies as their photon's path are distorted by the huge mass of dark matter in the galaxy cluster bending the fabric of spacetime.
Since the dark matter dominates, the photons from background galaxies trace the dark matter in the cluster. In this environment this distortion can be a weak, slight, change in shape, however it can an extreme event where galaxies are seen as huge arcs. I have spent much of my Phd working on mass mapping in galaxy clusters, using the weak regime. Although I have spent much time using weak lensing, I find strong lensing a vital tool in the study of galaxy clusters.
Shape Measurement
Through the measurement of weak lensing on galaxy clusters, much of my work has involved shape measurement codes. Shape measurement is an ongoing problem in weak gravitational lensing. The ability to measure distortions of a few percent in galaxies which are only slightly larger than the telescope point spread function requires extremely sophisticated methods. In my phd, I have had experience using Lensfit, which fits realistic models of galaxies to the images and in a bayesian framework determines the most likely parameters. I have also been using the moment based measurement code, RRG, which takes quadrupole moments of galaxies in order to determine its shape.
Flexion
Galaxy clusters are a great place to observe the full affect of gravitational lensing. From the weak, modest changes in ellipiticty to the formation of multiple images, the non-linear nature of spacetime distortion means that each regime has a great advantage and disadvantage. In the regime between these two extreme limits exists a reasonably untouched area called flexion.
This pseudo-strong lensing limit, galaxies are bent into bananas according to the third derviative of the lensing potential. Because it is the third derivative, it is extremely sensitive to small mass lumps meaning that the potential for high accuracy mass mapping is huge.
Unfortunately this is not a simpy solved problem, measuring bananas is extremely difficult since the distribution of light is shifted in a non-trivial manner.
The main research aim of my Ph.D thesis to measure the interaction cross section of dark matter using the statically averaged offset between mass components of in-falling substructure in to massive galaxy clusters.
It is predicted that in-falling sub-halos should experience the same behaviour as the bullet cluster and separate their associated dark matter and gas halos. Using the galaxy group members as a proxy for the direction of in-fall we should be able to make a robust measurement of the scattering cross-section of dark matter.
Gravitational Lensing
In order to determine the distribution of dark matter in galaxy clusters, we use the deformation of background source galaxies as their photon's path are distorted by the huge mass of dark matter in the galaxy cluster bending the fabric of spacetime.
Since the dark matter dominates, the photons from background galaxies trace the dark matter in the cluster. In this environment this distortion can be a weak, slight, change in shape, however it can an extreme event where galaxies are seen as huge arcs. I have spent much of my Phd working on mass mapping in galaxy clusters, using the weak regime. Although I have spent much time using weak lensing, I find strong lensing a vital tool in the study of galaxy clusters.
Shape Measurement
Through the measurement of weak lensing on galaxy clusters, much of my work has involved shape measurement codes. Shape measurement is an ongoing problem in weak gravitational lensing. The ability to measure distortions of a few percent in galaxies which are only slightly larger than the telescope point spread function requires extremely sophisticated methods. In my phd, I have had experience using Lensfit, which fits realistic models of galaxies to the images and in a bayesian framework determines the most likely parameters. I have also been using the moment based measurement code, RRG, which takes quadrupole moments of galaxies in order to determine its shape.
Flexion
Galaxy clusters are a great place to observe the full affect of gravitational lensing. From the weak, modest changes in ellipiticty to the formation of multiple images, the non-linear nature of spacetime distortion means that each regime has a great advantage and disadvantage. In the regime between these two extreme limits exists a reasonably untouched area called flexion.
This pseudo-strong lensing limit, galaxies are bent into bananas according to the third derviative of the lensing potential. Because it is the third derivative, it is extremely sensitive to small mass lumps meaning that the potential for high accuracy mass mapping is huge.
Unfortunately this is not a simpy solved problem, measuring bananas is extremely difficult since the distribution of light is shifted in a non-trivial manner.