Baryon Acoustic Oscillations (BAO) are a feature imprinted in the density field by acoustic waves travelling in the plasma of the early universe. Their fixed scale can be used as a standard ruler to study the geometry of the universe. BAO have been detected in the CMB and in the galaxy distribution, using correlation functions and power spectra. We searched for real-space structures associated with this feature -- spherical shells with a relatively small density contrast, surrounding high density central regions.
We designed a specific wavelet adapted to the search for shells, and used different mass tracers for the shells and for their centers. For the SDSS, we used the 'Main' catalogue galaxies for the shells, and LRGs as tracers of the high density central regions. We found BAO-size shell-like structures in the density field, with LRGs preferentially located close to the centres of the shells. As these shells are real spatial structures, the BAO phenomenon can be studied in detail by examining those shells; I describe preliminary results obtained by stacking of the shells.
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