Sunyaev-Zeldovich Effect and Circumgalactic Medium

Galaxy clusters contain the majority of their mass in dark matter, and the rest are mostly hot plasma of the intracluster medium (ICM). Thus the physical understanding of the galaxy clusters from their internal dynamics to their evolution associated with the galaxies inside is achieved by the observation of the ICM. As the cosmic microwave background (CMB) photons travel through the galaxy clusters and are scattered by the ICM, this interaction causes spectral distortion called the Sunyaev-Zel’dovich (SZ) effect. (Figure credit: Sayers et al. 2018)

At Caltech, I’m working with Professor Sunil Golwala and his group to study observational cosmology and galaxy formation using the SZ effect. The interaction between the galaxies and their surroundings is one of the key questions in current galaxy formation research. The circumgalactic medium (CGM) and the intergalactic medium (IGM) exchange matter and energy with the galaxies and regulate how quickly they form stars. The galaxy clusters, the most massive gravitationally bound system in the universe, serve as laboratories where we can observe the large-scale interplay and test various galaxy formation theories in the cosmological context.

Mapping the Baryonic Majority: Comprehensive Multi-Mission Analysis of the CGM and IGM

The internal ICM motion will be imprinted on the SZ signals; therefore, these observational studies may inform how to model the inflows of matter in the galaxies. Additionally, scaling down what we see in clusters may be helpful in understanding what happens in massive galaxies as well. The high-sensitivity millimeter-wavelength observation, including the future CMB surveys (e.g., CMB-S4, Simons Observatory), will allow us to understand galaxy formation by exploring the thermodynamic properties of CGM and IGM (Battaglia et al. 2019). I’m studying the observational probes using cosmological simulations such as IllustrisTNG, EAGLE, and FIRE.

A Multi-Probe Analysis of the 3-D Shapes and Non-Thermal Pressure in the XMM-Heritage Galaxy Clusters

The CHEX-MATE project is a 3 Msec XMM-Heritage program to study a Planck SZ selected sample of 118 clusters. These clusters were selected to provide galaxy cluster population in the local universe and in the highest mass regime. I work with Jack Sayers to perform a multi-probe three-dimensional triaxial analysis using the SZ, X-ray, and weak-lensing data. The study will provide a distribution of the three-dimensional shape of the galaxy clusters and the level of non-thermal pressure support in the ICM with the clean and well-characterized sample.

Simulations of science reach of future SZ effect measurements

We expect to be able to see the SZ signal directly from the hot component of the CGM of galaxies via stacking (Planck Collaboration 2013), or even from the individual galaxies using future large aperture telescopes (e.g., CSST). The wideband spectral observation in (sub)millimeter wavelengths is necessary to separate the SZ signals from the spectrum of typical radio galaxies or dusty star-forming galaxies. However, the SZ effect observations are not straightforward because of the external components that contribute to the flux in the overlapping wavelength region. I’m developing component separation techniques to remove CMB and extract the SZ signals from the simulations.


Sunil Golwala, Jack Sayers, Ted Macioce, Jim Bartlett

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