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|Title: ||Simulating large cosmology surveys with calibrated halo models|
|Authors: ||Lynn, Stuart|
|Supervisor(s): ||Peacock, John|
|Issue Date: ||23-Nov-2011|
|Publisher: ||The University of Edinburgh|
|Abstract: ||In this thesis I present a novel method for constructing large scale mock galaxy and halo
catalogues and apply this model to a number of important topics in modern cosmology.
Traditionally such mocks are created through first evolving a high resolution particle
simulation from a set of initial conditions to the present epoch, identifying bound
structures and their evolution, and finally applying a semi-analytic prescription for
galaxy formation. In contrast to this computationally expensive procedure, I use low
resolution simulations to obtain a density field that traces large scale modes. From this
background I sample the population statistics of halos: the number of halos which are
typically found within a region of a given overdensity, to produce a halo catalogue.
From the halo catalogue I then produce galaxies by appealing to the halo model.
In this model the expected number of galaxies within a halo and the distribution of
their properties is dependent on halo mass alone. By sampling conditional luminosity
functions for a number of populations of galaxies, I produce a galaxy catalogue with
luminosity and colour properties.
The aim of developing algorithm is not to probe the mechanics of galaxy formation
in great detail. It is instead intended as a method of rapidly producing mock galaxy
and halo catalogues rapidly on modern desktop computers. The approach we will take
is to try to distill the minimal algorithm required to achieve this and still provide useful
catalogues for observational cosmologists.
Both the conditional mass function and conditional luminosity functions required
for the algorithm are calibrated from the Millennium Simulation, one of the highest
resolution cosmology simulations to date, and its associated semi-analytic catalogues.
In Chapter 2 I examine these statistics and provide fits to the quantities of interest.
As a test of the method, in Chapter 3 I produce a halo and galaxy catalogue from
the same large scale modes as the Millennium Simulation. The clustering statistics of
galaxies and halos within this re-simulation are calculated and compared with those of
Con dent of the accuracy of the method, in Chapter 4 I populate a number of
simulations, each 8 times the volume of the Millennium Simulation, and study the
evolution of the Baryon Acoustic Oscillation signal. For each population (dark matter,
halos and galaxies) I fit the BAO in the power spectrum to obtain the shift in the BAO
In Chapter 5 I extend the algorithm to produce lightcones: simulated skies in
which the evolution of the Universe along the line of sight is accounted for. I simulate
the geometry and limitations of a major pending survey and calculate the expected
clustering signature I expect to see in both. The redshift space distortions induced by
peculiar velocities of galaxies along the line of sight are determined and their ability to
distinguish between gravity models is also explored.
In Chapter 6 I detail a further extension to the algorithm for simulating weak gravitational lensing surveys. I use the analytic 2D surface density pro files of NFW profiles
to dress each dark matter halo on a lightcone. The sum of these pro files over the entire
population can be used to construct high resolution maps of the convergence. From
these maps I calculate the spectrum of the convergence and compare with theoretical
Finally in Chapter 7 I discuss further possible applications and extensions of the
algorithm I have developed in this thesis.|
|Sponsor(s): ||Science and Technology Facilities Council (STFC)|
|Appears in Collections:||Physics thesis and dissertation collection|
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