The influence of baryons on the clustering of matter and weak lensing surveys

TL;DR

The paper addresses how baryons alter small-scale matter clustering and the weak lensing power spectrum, a crucial concern for forthcoming high-precision cosmic shear surveys. It adopts a controlled set of hydrodynamical simulations (DM-only, non-radiative gas, and gas with cooling and star formation) to quantify baryonic back-reaction on dark matter and total matter, as well as the resulting lensing signals. Key findings show gas clustering is suppressed while dark matter clustering is boosted for $k>1\,h\,\text{Mpc}^{-1}$, leading to total matter power suppression of up to about $1\%$ on $1<k<10\,h\,\text{Mpc}^{-1}$ and a boost up to $2\%$ (NR) or $\sim10\%$ (SF) near $k\approx20\,h\,\text{Mpc}^{-1}$; the weak lensing signal changes by less than $0.5\%$ at $\ell<1000$ but can reach $1$–$10\%$ at $1000<\ell<10000$, depending on the source redshift. These results imply that baryonic physics must be modeled to $\sim1\%$ accuracy to avoid biases in cosmological parameter inferences, and future lensing data could itself help constrain the underlying baryonic processes driving galaxy formation.

Abstract

Future weak lensing measurements of cosmic shear will reach such high accuracy that second order effects in weak lensing modeling, like the influence of baryons on structure formation, become important. We use a controlled set of state of the art cosmological simulations to quantify this effect by comparing pure N-body dark matter runs with corresponding hydrodynamical simulations, carried out both in non-radiative, and in dissipative form with cooling and star formation. In both hydrodynamical simulations, the clustering of the gas is suppressed while that of dark matter is boosted at scales k>1 h/Mpc. Despite this counterbalance between dark matter and gas, the clustering of the total matter is suppressed by up to 1 percent at 1<k<10 h/Mpc, while for k ~ 20 h/Mpc it is boosted, up to 2 percent in the non-radiative run and 10 percent in the run with star formation. The stellar mass formed in the latter is highly biased relative to the dark matter in the pure N-body simulation. Using our power spectrum measurements to predict the effect of baryons on the weak lensing signal at 100<l<10000, we find that baryons may change the lensing power spectrum by less than 0.5 percent at l<1000, but by 1 to 10 percent at 1000<l<10000. The size of the effect exceeds the predicted accuracy of future lensing power spectrum measurements and will likely be detected. Precise determinations of cosmological parameters with weak lensing, and studies of small-scale fluctuations and clustering, therefore rely on properly including baryonic physics.

Figures (3)

• Figure 1: The power spectrum of density fluctuations of each matter component in the non-radiative gas simulation (bottom panels), and in the gas cooling and star formation simulation (top panels), at redshifts $z=1$ and $z=0$. The results are compared with the spectrum of the pure dark matter simulation (black solid lines). The colored dotted lines, dashed lines, long dashed lines, and solid lines are plotted for the dark matter, gas, stellar and total matter density field, respectively.
• Figure 2: The influence of baryons on the clustering of each matter component. The plot shows the relative difference (in percent) of the power spectrum of each matter component in the gas simulations relative to the pure dark matter simulation. The results of the non-radiative run are plotted with red color, and those of the star formation run with green colors. The colored dotted lines, dashed lines, and solid lines are plotted for the dark matter and gaseous components, and the total matter density field, respectively. The stellar component in the star formation run is omitted here, as the difference can be easily infered from Figure \ref{['ps']}.
• Figure 3: The effect of baryons on the shear power spectrum $C_l$, expressed as relative difference (in percent) to the pure dark matter model. Here the source galaxies are assumed to be at redshifts $z_s=0.6$, $1.0$ and $1.5$, respectively. The dashed lines are the predictions from our non-radiative run, while the solid lines give the results for the star formation run.