On April 29 (Chilean time), we conducted a test polarization observation using five Japanese 7-m ACA (Atacama Compact Array) antennas and a Japanese ACA correlator for the first time.
A polarized radio wave oscillates in a specific direction. Polarization technique is commonly used in radio waves for network communications, and, in the field of astronomy, we use it to study magnetic field structures of astronomical objects. Polarization observation is very important because magnetic fields are assumed to be playing key roles in the evolution of the universe, especially in relation to the birth of stars and galaxies. Along with the reception of radio field intensity and frequencies, polarization observation with high accuracy is one of the main goals of ALMA.

The target object of this test observation is the quasar 1924-292 (3.9 billion years away from the Earth). The quasar has a supermassive black hole in its center and has a bright emission from the jets which are bursting out from the black hole at close to the speed of light. The results of this observation demonstrate that polarization can be detected with very high accuracy of below 1%. This is a great step forward for the realization of high-precision observation of cosmic magnetic fields with ALMA.

The picture below shows observation staff members with the polarization test results on the computer screen. From right: Hiroshi Nagai (Researcher at NAOJ), Neil Phillips (Joint ALMA Observatory), Shin’ichiro Asayama (Assistant Professor at NAOJ), Takahiro Naoi (Research Expert at NAOJ), and Kouichiro Nakanishi (Assistant Professor at NAOJ).

The figure below shows the quasar 1924-292. Detected polarization is indicated with white lines.