Weekly cosmology seminar

Sara Aliqolizadehsafari

Institute for Particle Physics and Astrophysics, ETH, Zurich

Separating Weak Gravitational Lensing and Galaxy Intrinsic Alignments in the Dark Energy Survey (DES)

Abstract: The assumption that galaxies’ orientations are randomly distributed in the universe is not sufficiently accurate when dealing with modern surveys and can lead to contamination of weak lensing measurements with a systematic bias called Intrinsic Alignment (IA).

This bias has to be dealt with properly so as to preserve the accuracy of recent weak lensing measurements. The alignment of elliptical galaxies, especially luminous red galaxies, with the local tidal field at large scales has been observed in recent years. At small scales, however, non-linearities can complicate this behavior. In this work, we have extracted the intrinsic alignment signal using two tomographic bins of DES Y1 source galaxies, 0.3<z<0.45 and 0.55<z<0.7, and the DES redMaGiC lens sample at 0.3<z<0.45. Our method is based on the fact that the measured lensing signal, ΔΣ, is the same for the two tomographic source bins since it depends only on the characteristics of the lens sample.

Statistically, the number of galaxies that contribute to the intrinsic alignment contamination signal is expected to reduce as the separation between lens and source sample increases. Error estimation is done via the Jackknife covariance method using 40 sub-samples. We have found IA signals using two different weighting schemes which both have a signal-to-noise ratio over 10. Finally, we have modeled the intrinsic alignment signal in the tidal alignment framework, using linear theory on large scales and a fully non-perturbative treatment of the one-halo scale. We have found that this model provides good agreement with the measured signal.

یکشنبه 5 دی 1400، ساعت 19:00

Sunday 26 December 2021 – 19:00 Tehran Time

اتاق سمینار مجازی –Virtual Seminar Room

https://vc.sharif.edu/ch/cosmology

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