REIONIZATION ON LARGE SCALES. II. DETECTING PATCHY REIONIZATION THROUGH CROSS-CORRELATION OF THE COSMIC MICROWAVE BACKGROUND

• Published in: The Astrophysical journal Vol. 776; no. 2; pp. 1 - 10
• Main Authors: Natarajan, A, Battaglia, N, Trac, H, Pen, U-L, Loeb, A
• Format: Journal Article
• Language: English
• Published: United States 20-10-2013
• Subjects: ANISOTROPY; ASTRONOMY; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Brackets; Correlation; CORRELATIONS; Cosmic microwave background; COSMOLOGY; DENSITY; ENERGY SPECTRA; FREQUENCY ANALYSIS; FREQUENCY DEPENDENCE; POLARIZATION; RED SHIFT; RELICT RADIATION; Small scale
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/776/2/82

We investigate the effect of patchy reionization on the cosmic microwave background (CMB) temperature. An anisotropic optical depth [tau](n) alters the TT power spectrum on small scales l > 2000. We make use of the correlation between the matter density and the reionization redshift fields to construct full sky maps of [tau](n). Patchy reionization transfers CMB power from large scales to small scales, resulting in a non-zero cross correlation between large and small angular scales. We show that the patchy [tau] correlator is sensitive to small root mean square (rms) values [tau] sub(rms) ~ 0.003 seen in our maps. We include frequency-independent secondaries such as CMB lensing and kinetic Sunyaev-Zel'dovich (kSZ) terms, and show that patchy [tau] may still be detected at high significance. Reionization models that predict different values of [tau] sub(rms) may be distinguished even for the same mean value [left angle bracket] [tau] [right angle bracket]. It is more difficult to detect patchy [tau] in the presence of larger secondaries such as the thermal Sunyaev-Zel'dovich, radio background, and the cosmic infrared background. In this case, we show that patchy [tau] may be detected if these frequency-dependent secondaries are minimized to [< ~]5 mu K (rms) by means of a multi-frequency analysis. We show that the patchy [tau] correlator provides information that is complementary to what may be obtained from the polarization and the kSZ power spectra.