X-ray Observations Of The Hot Gas In Clusters Of Galaxies And Cluster Galaxies

In the concordance∧cold dark matter (ACDM) cosmology, the geometry and dy-namics of the universe can be determined by a set of a few parameters. The main task of observational cosmology in the era of precision cosmology is to determine accurately those parameters. In ACDM, structures form hierarchically; i.e., lower mass objects form first, and subsequently undergo mergers and accretions to form more massive sys-tems. Clusters of galaxies are the largest gravitational bound systems and their mass functions are very sensitive to cosmological parameters, so they can be used as sensitive probes for cosmology. To do this, we need to measure their masses to a very high accu-racy. Meanwhile, clusters are also unique laboratory to explore various astrophysical processes and their influence on baryon evolution, including the environmental depen-dence of cluster galaxy evolution. Moreover, the astrophysical processes occurred in clusters also affect their mass determinations, hence the mass function, which ultimately limit the constraining power of clusters on cosmology. Thus, detailed examinations of various astrophysical processes in clusters are necessary for both cosmology and astro-physics. This thesis focuses on two astrophysical processes in clusters, cluster merger and ram pressure stripping, with discussions on their implications for cosmology and baryon evolution in clusters, respectively.In Chapter2, we study a merging cluster, PLCK G036.7+14.9, from the Chandra-Planck Legacy Program, which aims at obtaining the mass function of a low redshift (z<0.35) sample of the Planck early Sunyaev-Zeldovich (ESZ) cluster sample to constrain cosmological parameters. Our high resolution X-ray observations of PLCK G036.7+14.9reveal two close yet clearly separated subclusters, G036N and G036S, which were not resolved by previous ROSAT, optical or recent Planck observations. Spectral analysis confirms that the two subclusters are interacting. Based on both sub-clusters’morphologies and surface brightness profiles beyond the interaction region, temperature variations in the core regions, as well as a simplified dynamical model, we argue that the merger should be at an early stage and largely along the line-of-sight. G036N hosts a small moderate cool-core while G036S hosts at most a very weak cool-core, and this difference is unlikely to be caused by the ongoing merger. G036N also hosts an unresolved radio source; if extended, this radio source might be heating the gas in G036N’s core. The Planck SZ mass is higher than the X-ray mass of either sub-cluster, but lower than the X-ray mass of the whole cluster, due to that Planck does not resolve the subclusters and interpret the whole system as a single cluster. This could in-troduce significant bias to the mass function if such systems are common in the Planck ESZ sample. Thus, high resolution X-ray observations of the Planck ESZ sample are necessary to identify such systems and correct such a bias before applying the Planck SZ mass function to constrain cosmology.In Chapter3, we present the studies of a tail associated with a late-type galaxy, ESO137-002, in the nearby rich cluster A3627. This tail is caused by ram pressure strip-ping and is clear evidence for the influence of cluster environment on cluster galaxies. The Chandra data reveal a long (>40kpc) narrow (-3kpc) tail with a nearly constant width, which we interpret as stripped gas due to ram pressure. The tail has a nearly constant temperature along its length,-1keV, but a single thermal model gives a rather low abundance, a reflection of multiphase gas distribution in the tail. The mass ratio of the X-ray tail to the initial interstellar medium (ISM) of the galaxy is small, suggesting that the stripping should be at an early stage. The tail is "over-pressured" relative to the ambient intracluster medium (ICM) with the three models we tried, which could be due to the uncertainties in the abundance, thermal vs. non-thermal X-ray emission, or magnetic support in the ICM. There is also a Ha tail spatially coincident with the X-ray tail, as well as a secondary Ha tail. We compare the tails of ESO137-002with ESO137-001, another galaxy with similar tails studied in our previous work, as well as to simulations. We find that the tails of both galaxies have similarities and differences, while simulations have difficulties in quantitatively explaining them. The discovery of this tail provides new observational constraints on ram pressure stripping and provides a new environment for studying baryonic physics.In Chapter4, we briefly discuss our preliminary results on the study of stellar mass fractions of protoclusters. We select10protoclusters from the literature where stellar mass and total mass of the protocluster can be obtained or estimated, and assess their stellar mass fractions and stellar mass densities. We find that7protoclusters have much lower stellar mass fractions than their low redshift counterparts with the same total mass. By comparing their stellar mass densities with those from large surveys, we suggest that their low stellar mass fractions are real. The other3protoclusters, however, have similar stellar mass fractions as their low redshift counterparts with the same total mass. This could be due to that their total masses were more severely underestimated than their stellar masses, or stars formed earlier in them. Our results suggest that galaxies contribute very little to the total mass of ICM in nearby clusters of galaxies, while the bulk of it should be primordial.