The BOSS-WiggleZ overlap region I: Baryon Acoustic Oscillations

TL;DR

The paper analyzes BAO in the overlap between BOSS-CMASS and WiggleZ to obtain robust distance-scale measurements. Using density-field reconstruction and a suite of COLA mock catalogs, it demonstrates BAO detections in auto- and cross-correlation functions, and provides a covariance framework to combine WiggleZ and CMASS BAO constraints. The post-reconstruction results yield consistent $D_V r_s^{ m fid}/r_s$ values across tracers and with mock expectations, and the analysis finds no evidence for a relative velocity effect in the overlap region. The methodology enables rigorous cross-survey BAO combinations and paves the way for incorporating WiggleZ data into future CMASS DR12 cosmological constraints.

Abstract

We study the large-scale clustering of galaxies in the overlap region of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS sample and the WiggleZ Dark Energy Survey. We calculate the auto-correlation and cross-correlation functions in the overlap region of the two datasets and detect a Baryon Acoustic Oscillation (BAO) signal in each of them. The BAO measurement from the cross-correlation function represents the first such detection between two different galaxy surveys. After applying density-field reconstruction we report distance-scale measurements $D_V r_s^{\rm fid} / r_s = (1970 \pm 47, 2132 \pm 67, 2100 \pm 200)$ Mpc from CMASS, the cross-correlation and WiggleZ, respectively. We use correlated mock realizations to calculate the covariance between the three BAO constraints. The distance scales derived from the two datasets are consistent, and are also robust against switching the displacement fields used for reconstruction between the two surveys. This approach can be used to construct a correlation matrix, permitting for the first time a rigorous combination of WiggleZ and CMASS BAO measurements. Using a volume-scaling technique, our result can also be used to combine WiggleZ and future CMASS DR12 results. Finally, we use the cross-correlation function measurements to show that the relative velocity effect, a possible source of systematic uncertainty for the BAO technique, is consistent with zero for our samples.

Figures (19)

• Figure 1: Sky coverage of BOSS-CMASS DR11 (black) and WiggleZ (red). The left plot shows the north galactic cap (NGC), while the right plot shows the south galactic cap (SGC). Five of the six WiggleZ regions are covered by CMASS, with region S22 being only partly covered. We only plot a random fraction of $3\%$ of all galaxies.
• Figure 2: The overlap region between BOSS-CMASS (black) and WiggleZ (red). Most of the angular incompleteness is caused by WiggleZ, while the empty stripes in region N11 are caused by incomplete photometric data in CMASS. To generate these regions, we divided the sky into $0.1\,\deg^2$ bins and included all bins which contain CMASS as well as WiggleZ random galaxies. We only plot a random fraction of $10\%$ of all galaxies.
• Figure 3: Redshift distribution of CMASS-BW (red) and WiggleZ-BW (blue) combining the five separate regions.
• Figure 4: The correlation functions of CMASS-BW (top), WiggleZ-BW (bottom) and the cross-correlation (middle) in the overlap regions between CMASS and WiggleZ. The grey lines show the correlation functions for the five individual sub-regions (see Figure \ref{['fig:sky']}), while the colored data points show the combined correlation functions calculated from Eq. \ref{['eq:combine']}. The error bars are the diagonal of the combined covariance matrices (see Figure \ref{['fig:covs']}). Note, that the scatter in the grey lines does not represent the error in the data points, since each grey line corresponds to a different volume and is weighted accordingly. The black lines show the best fit to the individual correlation functions corresponding to the upper part of Table \ref{['tab:results']}.
• Figure 5: The measured correlation coefficient before (blue) and after (black) density field reconstruction. The dashed line shows the expectation of linear theory. The blue data points are shifted by $0.5\,$Mpc$/h$ to the right for clarity. The solid lines indicate the mean correlation coefficient of the mock realizations before (red) and after (magenta) density field reconstruction. The error on the data points is derived from the variations in the $480$ mock catalogues (grey lines). When fitting the correlation coefficient in Section \ref{['sec:relvel']} we only use the data before reconstruction, since we do not have a model for the correlation function post reconstruction.