First Evidence of Intrinsic Alignments of Red Galaxies at z>1: Cross-correlation between CFHTLenS and FastSound Samples

Speaker

Motonari Tonegawa
Asia Pacific Center for Theoretical Physics (Republic of Korea)

Abstract

Intrinsic alignment (IA) is a coherent alignment of galaxy orientations in the large-scale structure caused by the local gravitational interaction. Because it is a major contaminant for weak lensing cosmology, where the source galaxies are assumed to be randomly oriented, understanding how large it is and how it depends on scale and time (redshift) will be crucial for ongoing and future weak lensing studies. Moreover, IA contains valuable information about dynamical aspects of galaxy formation and evolution. Observations have shown that red galaxies exhibit strong IA at z≤1 while blue galaxies do not, implying different mechanisms of IA for different galaxy types. The next important and interesting question is whether this is true for higher redshifts. In this talk, I report the first measurement of IA of red galaxies at z>1. Using the FastSound spectroscopic and CFHTLenS shape samples, we measured the density-ellipticity cross-correlation function and found ~2.5 σ level signals. We carefully performed sanity checks and concluded that the signals are indeed IA-induced. The derived amplitude parameter for the linear alignment model is higher than low-redshift counterparts, and it is translated into ~20% contamination to the weak lensing power spectrum for red galaxies.

Date and Time

December 23 2021
4pm KST (= 7am UTC)

Recording

Link to the recording on Youtube