New method to revisit the gravitational lensing analysis of the Bullet Cluster u
Theoretical Physics Letters
2023 ° 22(06) ° 0631-7361
Youngsub Yoon a,b Jong-Chul Park,a,b,1 Ho Seong Hwangc,d ------------------------------------- a Department of Physics and Institute of Quantum Systems (IQS) Chungnam National University, Daejeon 34134, Republic of Korea b Particle Theory and Cosmology Group, Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS), Daejeon, 34126, Republic of Korea c Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea d SNU Astronomy Research Center, Seoul National University, Seoul 08826, Republic of Korea
Gravitational lensing studies of the Bullet Cluster suggested convincingly in favour of the existence of dark matter. However, it was performed without the knowledge of the original orientation of each galaxy before gravitational lensing. A potential improvement to this issue lies in the measurement of the original orientation from the polarization direction of radio waves emitted from each galaxy. In this context, Francfort et al. derived a formula that can utilize the information about the original orientation of each galaxy to obtain what is called shear. However, we demonstrate that shear in their formula should be replaced by reduced shear when the change in sizes of images of galaxies is taken into account. As the previous gravitational lensing analysis of the Bullet Cluster used reduced shear, we suggest applying our improved formula directly for the reanalysis once we obtain the polarization direction of radio waves. In particular, we show that our new formula can yield a more accurate analysis than the previous one, if the polarization direction can be measured more precisely than 10◦.