Constraints on sigma_8 from galaxy clustering in N-body simulations and semi-analytic models

TL;DR

This study constrains sigma_8 using galaxy clustering data from SDSS and 2dFGRS, employing rescaled N-body simulations and semi-analytic models to predict galaxy bias and derive a nearly pure cosmological constraint.

Contribution

It introduces a method to constrain sigma_8 by predicting galaxy bias directly from models, reducing nuisance parameters and systematic errors.

Findings

Estimated sigma_8 = 0.97 +/- 0.06 from galaxy clustering.

Results are consistent across different galaxy samples and luminosity thresholds.

The derived sigma_8 is higher than some previous analyses, prompting further investigation.

Abstract

We generate mock galaxy catalogues for a grid of different cosmologies, using rescaled N-body simulations in tandem with a semi-analytic model run using consistent parameters. Because we predict the galaxy bias, rather than fitting it as a nuisance parameter, we obtain an almost pure constraint on sigma_8 by comparing the projected two-point correlation function we obtain to that from the SDSS. A systematic error arises because different semi-analytic modelling assumptions allow us to fit the r-band luminosity function equally well. Combining our estimate of the error from this source with the statistical error, we find sigma_8=0.97 +/- 0.06. We obtain consistent results if we use galaxy samples with a different magnitude threshold, or if we select galaxies by b_J-band rather than r-band luminosity and compare to data from the 2dFGRS. Our estimate for sigma_8 is higher than that obtained for other analyses of galaxy data alone, and we attempt to find the source of this difference. We note that in any case, galaxy clustering data provide a very stringent constraint on galaxy formation models.