CMB distortion from circumgalactic gas

Abstract

We study the Sunyaev-Zel'dovich (SZ) distortion of the cosmic microwave background radiation (CMBR) from extensive circumgalactic gas (CGM) in massive galactic halos. Recent observations have shown that galactic halos contain a large amount of X-ray emitting gas at the virial temperature, as well as a significant amount of warm OVI absorbing gas. We consider the SZ distortion from the hot gas in those galactic halos in which the gas cooling time is longer than the halo destruction time scale. We show that the SZ distortion signal from the hot gas in these galactic halos at redshifts $z\approx 1\hbox{--}8$ can be significant at small angular scales ($\ell\sim 10^4$), and dominate over the signal from galaxy clusters. The estimated SZ signal for most massive galaxies (halo mass $\ge 10^{12.5}$ M$_\odot$) is consistent with the marginal detection by {\it Planck} at these mass scales. We also consider the SZ effect from warm circumgalactic gas. The integrated Compton distortion from the warm OVI absorbing gas is estimated to be $y\sim 10^{-8}$, which could potentially be detected by experiments planned for the near future. Finally, we study the detectability of the SZ signal from circumgalactic gas in two types of surveys, a simple extension of the SPT survey and a more futuristic cosmic variance-limited survey. We find that these surveys can easily detect the kSZ signal from CGM. With the help of a Fisher Matrix analysis, we find that it will be possible for these surveys to constrain the gas fraction in CGM, after marginalizing over cosmological parameters, to $\le 33$\%, in case of no redshift evolution of the gas fraction.