On the origin of intrinsic alignment in cosmic shear measurements: an analytic argument

Camelio, Giovanni; Lombardi, Marco

doi:10.1051/0004-6361/201425016

Cited by 15 publications

(15 citation statements)

References 47 publications

(108 reference statements)

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“…Furthermore, the potential of the system needs to be consistent with the particle distribution in configuration-and velocity-space, and cannot be chosen independently. These are two points in which we hope to improve the investigation by Camelio & Lombardi (2015).…”

Section: Theoretical Backgroundmentioning

confidence: 88%

“…We also emphasise that our model assumes a spherically symmetric, self-gravitating halo in virial equilibrium, with an isotropic velocity distribution with constant dispersion. A consistent solution for such a system would be the singular isothermal sphere with a density profile ρ ∝ 1/r 2 , for which we need to assume a cut-off radius in order to obtain finite values for the quadrupole moments, similarly to Camelio & Lombardi (2015). Our virial argument, on the other hand, does not differentiate between the dark matter and stellar components and, in particular, does not assume a potential of the unperturbed galaxy.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

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The mass dependence of dark matter halo alignments with large-scale structure

Piras

Joachimi

Schäfer

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Tidal gravitational forces can modify the shape of galaxies and clusters of galaxies, thus correlating their orientation with the surrounding matter density field. We study the dependence of this phenomenon, known as intrinsic alignment (IA), on the mass of the dark matter haloes that host these bright structures, analysing the Millennium and Millennium-XXL N-body simulations. We closely follow the observational approach, measuring the halo position-halo shape alignment and subsequently dividing out the dependence on halo bias. We derive a theoretical scaling of the IA amplitude with mass in a dark matter universe, and predict a power-law with slope β M in the range 1/3 to 1/2, depending on mass scale. We find that the simulation data agree with each other and with the theoretical prediction remarkably well over three orders of magnitude in mass, with the joint analysis yielding an estimate of β M = 0.36 +0.01 −0.01 . This result does not depend on redshift or on the details of the halo shape measurement. The analysis is repeated on observational data, obtaining a significantly higher value, β M = 0.56 +0.05 −0.05 . There are also small but significant deviations from our simple model in the simulation signals at both the high-and low-mass end. We discuss possible reasons for these discrepancies, and argue that they can be attributed to physical processes not captured in the model or in the dark matter-only simulations.

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Section: Theoretical Backgroundmentioning

confidence: 88%

Section: Theoretical Backgroundmentioning

confidence: 99%

The mass dependence of dark matter halo alignments with large-scale structure

Piras

Joachimi

Schäfer

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…If there is dynamical equilibration between the dark matter and the stellar components, one can expect that the shape of the luminous component reflects the shape of the dark matter halo. If the halo is now embedded into the large-scale structure, gravitational tidal fields will distort the potential of the halo and the luminous component rearranges itself while maintaining virial equilibrium as long as the gravitational shear is not strong enough to disrupt the halo (Camelio & Lombardi 2015). For sufficiently small tidal shears one can expect a linear relationship between the observed (projected) shape and the strength of the tidal fields.…”

Section: Early-type Galaxiesmentioning

confidence: 99%

Galaxy Alignments: An Overview

et al. 2015

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The alignments between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe. We provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience. The development of the field over the past one hundred years is briefly reviewed. We also discuss the impact of galaxy alignments on measurements of weak gravitational lensing, and discuss avenues for making theoretical and observational progress over the coming decade.

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“…The limiting case of z IA = z obs is the "instantaneous alignment" scenario. For further discussion on this topic, see [10,22,31]. At leading order, the impact of alignment epoch can be absorbed into a redshiftdependent amplitude, A(z), and eq.…”

Section: Alignment Epochmentioning

confidence: 99%

Tidal alignment of galaxies

Blazek

Vlah

Seljak

2015

J. Cosmol. Astropart. Phys.

164

198

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Abstract.We develop an analytic model for galaxy intrinsic alignments (IA) based on the theory of tidal alignment. We calculate all relevant nonlinear corrections at one-loop order, including effects from nonlinear density evolution, galaxy biasing, and source density weighting. Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales. This effect may be responsible for much of the luminosity dependence in IA observations. The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields. We also consider the impact of smoothing the tidal field on halo scales. We compare the performance of this consistent nonlinear model in describing the observed alignment of luminous red galaxies with the linear model as well as the frequently used "nonlinear alignment model," finding a significant improvement on small and intermediate scales. We also show that the cross-correlation between density and IA (the "GI" term) can be effectively separated into source alignment and source clustering, and we accurately model the observed alignment down to the one-halo regime using the tidal field from the fully nonlinear halo-matter cross correlation. Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting nonlinear processes that must be considered when modeling IA on these scales. Finally, we discuss tidal alignment in the context of cosmic shear measurements.

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On the origin of intrinsic alignment in cosmic shear measurements: an analytic argument

Cited by 15 publications

References 47 publications

The mass dependence of dark matter halo alignments with large-scale structure

The mass dependence of dark matter halo alignments with large-scale structure

Galaxy Alignments: An Overview

Tidal alignment of galaxies

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