Improving baryon acoustic oscillation measurement with the combination of cosmic voids and galaxies

TL;DR

This paper presents a method combining galaxy and void data to enhance BAO measurements, achieving about 10-18% improved constraints in simulations and real data, with potential for larger gains in future surveys.

Contribution

It introduces a combined analysis of galaxies and voids with a modified BAO model and a new 2PCF estimator, improving BAO constraints beyond previous galaxy-only methods.

Findings

Joint galaxy-void analysis improves BAO constraints by ~10%.

Modified BAO model accounts for void exclusion patterns.

Application to BOSS DR12 data shows 18% improvement at low redshift.

Abstract

We develop a methodology to optimise the measurement of Baryon Acoustic Oscillation (BAO) from a given galaxy sample. In our previous work, we demonstrated that one can measure BAO from tracers in under-dense regions (voids). In this study, we combine the over-dense and under-dense tracers (galaxies & voids) to obtain better constraints on the BAO scale. To this end, we modify the de-wiggled BAO model with an additional parameter to describe both the BAO peak and the underlying exclusion pattern of void 2PCFs. We show that after applying BAO reconstruction to galaxies, the BAO peak scale of both galaxies and voids are unbiased using the modified model. Furthermore, we use a new 2PCF estimator for a multi-tracer analysis with galaxies and voids. In simulations, the joint sample improves by about 10% the constraint for the post-reconstruction BAO peak position compared to the result from galaxies alone, which is equivalent to an enlargement of the survey volume by 20%. Applying this method to the BOSS DR12 data, we have an 18% improvement for the low-z sample (0.2<z<0.5), but a worse constraint for the high-z sample (0.5<z<0.75), which is consistent with statistical fluctuations for the current survey volume. Future larger samples will give more robust improvements due to less statistical fluctuations.