Fisher forecast for the BAO measurements from the CSST spectroscopic and photometric galaxy clustering

TL;DR

This paper forecasts how combining spectroscopic and photometric galaxy surveys from the upcoming CSST can significantly improve BAO distance measurements, demonstrating a robust method for future cosmological analyses.

Contribution

It introduces a Fisher matrix-based forecast showing over 30% improvement in BAO distance constraints by cross-correlating spectroscopic and photometric galaxy data from CSST.

Findings

Over 30% improvement in BAO distance constraints at z=1.0-1.2

Robustness against systematic effects like noise and redshift errors

Comparison with other Stage-IV surveys for context

Abstract

The China Space Station Telescope (CSST) is a forthcoming Stage IV galaxy survey. It will simultaneously undertake the photometric redshift (photo-z) and slitless spectroscopic redshift (spec-z) surveys mainly for weak lensing and galaxy clustering studies. The two surveys cover the same sky area and overlap on the redshift range. At $z>1$, due to the sparse number density of the spec-z sample, it limits the constraints on the scale of baryon acoustic oscillations (BAO). By cross-correlating the spec-z sample with the high density photo-z sample, we can effectively enhance the constraints on the angular diameter distances $D_A(z)$ from the BAO measurement. Based on the Fisher matrix, we forecast a $\geq$ 30 per cent improvement on constraining $D_A(z)$ from the joint analysis of the spec-z and cross galaxy power spectra at $1.0<z<1.2$. Such improvement is generally robust against different systematic effects including the systematic noise and the redshift success rate of the spec-z survey, as well as the photo-z error. We also show the BAO constraints from other Stage-IV spectroscopic surveys for the comparison with CSST. Our study can be a reference for the future BAO analysis on real CSST data. The methodology can be applied to other surveys with spec-z and photo-z data in the same survey volume.