Lectura de tesi:"Paint it black: Weak Lensing Analysis of an All-Sky Simulation"

  • Autor/Doctorand: Carlos López Arenillas
  • Dia: Divendres, 24 de gener de 2014
  • Hora: 12:00
  • Lloc: Sala de Graus (aulari)
  • Tribunal:​
    • President: Dr.  Gustavo Yepes Alonso
    • Secretari: Dr.  Jaume Garriga Torres 
    • Vocal: Dr.  Christopher Bonnett 
    • Suplents: Dr.  Martin Crocce
      Dr.  Francisco Javier Castander 
      Dr.  Ramón Miquel Pascual
  • Directors/Tutors: Dr. Enrique Gaztañaga Balbás (Director).
    Dr. Alberto Manrique Oliva (Tutor).
  • Resum: 

    This Thesis is concerned with one of the most promising probes to constrain the "Dark Universe", and, particularly, the dark matter distribution. Based on MICE cosmological simulation, and the all-sky convergence maps generated by Fosalba et al. (2008), we perform a mass calibration of the dark matter halos there contained up to z=1. In order to do that, we analyse the average halo density profiles of all the halos with masses ranging from 5x1013 to 3.751x1014 M/h , divided into four mass bins and three redshift bins. Through this analysis we address two main issues: the relatively low mass resolution of the simulation (mp=2.34x1011 M/h ) and the relatively high softening length (lsoft=50 Kpc/h). We do that by using a two-step procedure. First, we simulate analytical pure NFW density profiles (with different mass resolutions) using two input values: the virial radii of MICE halos and the expected concentrations, according to the fixed mass-concentration relation from Oguri and Hamana (2011). Second, we model the effect of the softening length with a Gaussian filter, smoothing the halo core. The results show that MICE halos are, in average, NFW halos. Best-fit NFW radii are in very good agreement with the average radii of our samples, overestimating the data by 1%, but best-fit NFW concentrations are in average 50% lower than the expected values. It is possible to account for part of this deviation by distinguishing between relaxed and unrelaxed halos, finding that, depending on the degree of relaxedness, the improvement can be as high as 30%. We also find that the analytical NFW halos simulated with MICE mass resolution have an overall concentration 40% lower than the input concentration, in the case of 3D profiles, and 25% lower in that of the projected profiles.
    The Gaussian-smoothed NFW profile is a good approximation for our projected halos. Additionally, we analyse the morphology of the halos, characterizing their triaxiality at R200 and calculating their orientation with respect to the line-of-sight (LOS). MICE halos tend to adopt a more prolate morphology, as might be expected from a LCDM simulation (Shaw et al. 2006), and the percentage of prolate halos grows as their mass grows. The mass resolution is, nonetheless, not good enough to draw conclusive inferences from the shape analysis, but it allows us to discern a trend and estimate the effect of halo shape and orientation on the weak lensing masses. Finally, we use the all-sky convergence maps to study the scatter in mass measurements of MICE halos.
    We determine the intrinsic scatter in the recovered masses by assuming the smoothed NFW profile as the true profile, and creating two new convergence maps from different mass cuts. We estimate also the scatter due to the correlated structure by studying the angles between the major axes of the halos and the LOS, and also that due to projection effects (i.e. all the dark matter between observer and source).

    We find an irreducible scatter (intrinsic) of 10-14%, a scatter around a 30% of the intrinsic one due to correlated structure, and a scatter around 40-70% of the intrinsic one due to projection effects. The size of our halo sample allows us to improve the characterization of the cosmic noise, of great importance for present and future surveys. 


Dijous, 23 Gener, 2014