http://arxiv.org/abs/1908.05765

The interpretation of upcoming weak gravitational lensing surveys depends critically on our understanding of the matter power spectrum on scales $k < 10 h/\mathrm{Mpc}$, where baryonic processes are important. In this paper we study the impact of gas flows associated with galaxy formation on the matter power spectrum using a halo model that treats the stars and gas separately from the dark matter distribution. The baryonic components are constrained empirically: the hot gas using fits to X-ray observations of groups and clusters of galaxies, and the stellar component using a halo occupation distribution. Since X-ray observations cannot generally measure the hot gas content outside $r_\mathrm{500c}$, we vary the gas density profiles beyond this radius. Compared with dark matter only models, we find a total power suppression of $1\%$ ($5\%$) on scales $0.2-1 h/\mathrm{Mpc}$ ($0.5-2 h/\mathrm{Mpc}$), where lower baryon fractions result in stronger suppression. We show that groups of galaxies ($10^{13} < m_\mathrm{500c} / (M_\odot/h) < 10^{14}$) dominate the total power at all scales $k \lesssim 10 h/\mathrm{Mpc}$. We illustrate the importance of measuring accurate halo masses by comparing models that do and do not account for a hydrostatic bias of $1-b=0.7$ in the halo masses from X-ray observations. We find that using biased halo masses results in an underestimation of the power suppression of up to $4\%$ at $k=1 h/\mathrm{Mpc}$. Contrary to work based on hydrodynamical simulations, our conclusion that baryonic effects can no longer be neglected is not subject to uncertainties associated with our poor understanding of feedback processes. Our findings highlight the need for observations to probe the outskirts of groups and clusters since these observations are the most constraining for the power suppression on scales $k \lesssim 1 h/\mathrm{Mpc}$.

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S. Debackere, J. Schaye and H. Hoekstra
Mon, 19 Aug 19
14/46

Comments: 21 pages, 19 figures, submitted to MNRAS