On cooling flows and the Sunyaev-Zel'dovich effect

Abstract

We study the effect of cooling flows in galaxy clusters on the Sunyaev-Zel'dovich (SZ) distortion and the possible cosmological implications. The SZ effect, alongwith X-ray observations of clusters, is used to determine the Hubble constant, $H_{\circ}$. Blank sky surveys of SZ effect are being planned to constrain the geometry of the universe through cluster counts. It is also known that a significant fraction of clusters has cooling flows in them, which changes the pressure profile of intracluster gas. Since the SZ decrement depends essentially on the pressure profile, it is important to study possible changes in the determination of cosmological parameters in the presence of a cooling flow. We build several representative models of cooling flows and compare the results with the corresponding case of gas in hydrostatic equilibrium. We find that cooling flows can lead to an overestimation of the Hubble constant. Specifically, we find that for realistic models of cooling flow with mass deposition (varying $\dot m$ with radius), there is of the order $\sim 10 %$ deviation in the estimated value of the Hubble constant (from that for gas without a cooling flow) even after excluding $ \sim 80 %$ of the cooling flow region from the analysis. We also discuss the implications of using cluster counts from SZ observations to constrain other cosmological parameters, in the presence of clusters with cooling flows.