Thesis Topic: Study of the intracluster medium (ICM) from observations of galaxy clusters with ALMA

 

Thesis Supervisors:

 Paola Andreani (ESO)

 Tony Mroczkowski (ESO)

Abstract

Galaxy clusters are large, nearly representative volumes of the universe, having baryon to dark matter mass ratios that approach the universal baryon fraction. The baryonic component is predominantly in the hot intracluster medium (ICM), which has traditionally been studied through X-ray observations. However, the millimeter band provides an alternative window on the ICM through the Sunyaev-Zel'dovich Effect (SZE), which is due to inverse Compton scattering of photons from the Cosmic Microwave Background (CMB) by hot ICM electrons. The SZE has two main forms, both redshift independent in surface brightness, unlike emission mechanisms which suffer dimming, making it a powerful complement to X-ray observations, particularly at high redshift. The dominant one is the thermal SZE, which scales as integrated line of sight pressure, and the secondary is the kinetic SZE, which scales as the product of peculiar velocity and electron opacity through the ICM. These two SZEs are separable at bands imaged by the Atacama Large Millimeter/Submillimeter Array (ALMA), which can now image the SZEs at unprecedented resolution and sensitivity (see Kitayama et al. 2016, Basu et al. 2016).

1. Use available ALMA data towards clusters of galaxies in 2 or more bands

2. Reduce and re-imaging the data using the CASA scripts available in the archive, tuning the parameters to improve imaging fidelity.

3. Modify the scripts to improve the signal to noise ratio, homogeneous data reduction (mostly redoing the imaging), with different gridding algorithms.

4. Extract the point sources from the maps, which negatively impact the signals from the SZE.

5. Extract the diffuse the Sunyaev-Zeldovich effect signal from the observations.

6. Compare the recoverd SZE signal with simulated observations, determined using X-ray data and SZE data from other instruments.