Intrinsic correlations of galaxy sizes and luminosities in weak lensing

  • Sandro Ciarlariello

Student thesis: Doctoral Thesis


Correlations of the observed sizes and luminosities of galaxies can be used to estimate the magnification that arises through weak gravitational lensing. However, the intrinsic properties of galaxies can be similarly correlated through local physical effects, and these present a possible contamination to the weak lensing estimation.
In this thesis we model these intrinsic correlations using the halo model, assuming that both the sizes and luminosities of galaxies reflect the mass in the associated halo, assuming the observed galaxy properties correlate closely with the mass of the haloes and sub-haloes. Larger and more luminous galaxies live in more massive haloes, and even if the sub-halo population is largely independent of the halo mass, the sizes and luminosities of the largest sub-haloes will still be limited by the total halo mass. We use this simple model to predict what would be observed for a magnification estimator based on galaxy sizes and magnitudes, and how the intrinsic signal correlates with the true lensing convergence. Additionally, we include in our analysis the effects of cuts in the sample and we model the size-magnitude distribution and study how the cuts in the survey affect the intrinsic mean size and magnitude as well as the inferred convergence power spectrum when using galaxy sizes and magnitudes.
Studying these correlations is important both to improve our understanding of galaxy properties and because they are a potential systematic for weak lensing size magnification measurements. Our model assumes that the density field drives these intrinsic correlations and we also model the distribution of satellite galaxies. We calculate the possible contamination to measurements of lensing convergence power spectrum from galaxy sizes and luminosities, and show that the cross-correlation of intrinsic properties with convergence is potentially an important systematic. We also explore how these intrinsic correlations may affect surveys with different redshift depth. We find that, in this simple approach, intrinsic size and luminosities correlations cannot be neglected in order to estimate lensing convergence power spectrum for constraining cosmological parameters.
Date of AwardSept 2016
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorRobert Crittenden (Supervisor)

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