Baryon acoustic oscillations with the cross-correlation of spectroscopic and photometric samples

The baryon acoustic oscillation (BAO) measurement requires a sufficiently dense sampling of large-scale structure tracers with spectroscopic redshift, which is observationally expensive especially at high redshifts z greater than or similar to 1. Here we present an alternative route of the BAO analysis that uses the cross-correlation of sparse spectroscopic tracers with a much denser photometric sample, where the spectroscopic tracers can be quasars or bright, rare galaxies that are easier to access spectroscopically. We show that measurements of the cross-correlation as a function of the transverse comoving separation rather than the angular separation avoid a smearing of the BAO feature without mixing the different scales at different redshifts in the projection, even for a wide redshift slice delta z similar or equal to 1. The bias, scatter and catastrophic redshift errors of the photometric sample affect only the overall normalization of the cross-correlation which can be marginalized over when constraining the angular diameter distance. As a specific example, we forecast the expected accuracy of the BAO geometrical test via the cross-correlation of the Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS) spectroscopic quasar sample with a dense photometric galaxy sample that is assumed to have a full overlap with the SDSS/BOSS survey region. We show that this cross-correlation BAO analysis allows us to measure the angular diameter distances to a fractional accuracy of about 10 per cent at each redshift bin over 1 less than or similar to z less than or similar to 3, if the photometric redshift errors of the galaxies, Sigma(z)/(1 + z), are better than 10-20 per cent level.