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A Perturbative Model for the Intrinsic Alignments of Galaxies


Schmitz, Denise Marie (2019) A Perturbative Model for the Intrinsic Alignments of Galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/HZ7G-1048.


Intrinsic alignments (IA), correlations between the intrinsic shapes and orientations of galaxies on the sky, are both a significant systematic in weak lensing and a probe of the effect of large-scale structure on galactic structure and angular momentum. In the era of precision cosmology, it is thus especially important to model IA with high accuracy.

Efforts to use cosmological perturbation theory to model the dependence of IA on the large-scale structure have thus far been relatively successful. However, extant models have not been made fully self-consistent to arbitrary order in perturbation theory and do not consistently account for time evolution. In particular, advection of galaxies due to peculiar velocities alters the impact of IA, because galaxy positions when observed are generally different from their positions at the epoch when IA is believed to be set.

In this work, we evolve the galaxy IA from the time of galaxy formation to the time at which they are observed, including the effects of this advection, and show how this process naturally leads to a dependence of IA on the velocity shear. We then incorporate this time evolution into a fully self-consistent perturbative formalism for a passively evolving IA model. We demonstrate this formalism first at second order as a proof of concept, then at third order for application to observationally relevant two-point correlations at one-loop order.

We also discuss the implications of the time-evolved IA model for systematic errors in weak lensing as well as for studies of galaxy formation and evolution. We find that considering advection introduces nonlocality into the bispectrum, and that the degree of nonlocality represents the memory of a galaxy's path from the time of its formation to the time of observation. We discuss how this result can be used to constrain the redshift at which IA is determined and provide Fisher estimation for the relevant measurements using the example of SDSS-BOSS.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Astronomy, astrophysics, cosmology, galaxy formation, galaxy evolution, large-scale structure, perturbation theory
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Astrophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hopkins, Philip F.
Group:TAPIR, Astronomy Department
Thesis Committee:
  • Steidel, Charles C. (chair)
  • Hirata, Christopher M.
  • Mawet, Dimitri
  • Doré, Olivier P.
  • Hopkins, Philip F.
Defense Date:9 May 2019
Funding AgencyGrant Number
Record Number:CaltechTHESIS:05312019-144001688
Persistent URL:
Related URLs:
URLURL TypeDescription for chapters 2-4
Schmitz, Denise Marie0000-0001-6297-9312
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11587
Deposited By: Denise Schmitz
Deposited On:05 Jun 2019 20:29
Last Modified:02 Dec 2022 19:57

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