|dc.contributor.author||Harvey, David Richard||
|dc.description.abstract||The dark matter paradigm has been a great source of speculation in both the 20th
and 21st Centuries. Since its proposed existence in 1933, the mounting evidence
has led to this theoretical particle becoming one of the greatest mysteries of
modern physics. However, despite its dominant presence in the Universe, little is
known about its nature and how it behaves. In this thesis I critically analyse one
particular property of dark matter: the self-coupling.
The self-interacting dark matter paradigm hypothesises that dark matter is
not collisionless as assumed in most cosmological simulations, and in-fact has
some probability that it will scatter off itself. Such a self-coupling will resolve
many discrepancies that exist between observations and theory, particularly on
small, non-linear scales. Moreover, any detection of a self-interaction cross-section
will place considerable limitations on the acceptable particle physics models of
dark matter and hence has grown to become an important question.
In this thesis I develop and implement a method to constrain the self-interaction
cross-section of dark matter that exploits continually accreting and
merging groups of galaxies as they fall into galaxy clusters. Utilising the
ubiquitous nature of accreting substructure, I measure the offsets between
dark matter and baryonic gas as they become separated due to their differing
interaction properties. Studying this effect over a sample of events, I will be able
to make the first ever statistical estimate of the cross-section of dark matter,
while averaging over many different unknown merging scenarios.
I begin my thesis by deriving an analytical description of sub-halo in-fall,
allowing me to constrain dark matter self-interaction models directly from
observations. In this study, I find that current archival data should be able to
detect a difference in the dynamical behaviour of dark matter and standard model
particles at 6σ, and measure the total interaction cross-section σDM/m with 68%
confidence limits of ±1 cm2g-1.
Having constructed a new method to derive constraints on the cross-section
of dark matter I carry out a study into the potential systematics that may affect
a measurement. I determine the accuracy of weak gravitational lensing, which is
the distortion of light due to intervening mass, as a tool to estimate the positions
of substructure in galaxy clusters. I find that the public Lenstool software can
measure the position of individual 1:5 x 1013Mʘ peaks with ~ 0:3" systematic
bias, as long as they are at least ~ 30" from the cluster centre.
Finally, I develop a pipeline that can analyse a sample of inhomogeneous observations
from The Hubble Space Telescope and the Chandra X-ray Observatory.
By measuring the positions of dark matter, gas and galaxies for 68 individual
merging events, from a total of 28 galaxy clusters, I detect a 7:4σ offset between
gas and an unobserved dark mass. I make the first ever measurement of cross-section
of dark matter from a sample of clusters finding σDM < 0:50cm2/g [95%
CL], the best constraints to date. In addition to this I find that the brightest
group galaxy in-fact tends to lead the dark matter halo during merging events.
Although evidence for the existence of interacting dark matter, I conclude that
the astrophysics of the BCG is complicated, and that this apparent directional
bias should be considered in all galaxy cluster analyses. Moreover, I show that
this technique is easily extendable for future surveys that have larger samples of
galaxy clusters, with constraints of σDM < 0:001cm2/g potentially attainable.||en
|dc.contributor.sponsor||Science and Technology Facilities Council (STFC)||en
|dc.publisher||The University of Edinburgh||en
|dc.relation.hasversion||Dark matter astrometry: accuracy of subhalo positions for the measurement of self-interaction cross-sections., Harvey D., Massey R., Kitching T., Taylor A., Jullo E., Kneib J. P., Tittley E. and Marshall P., 2013,MNRAS, 433, 151.||en
|dc.relation.hasversion||On the cross-section of dark matter using substructure infall into galaxy clusters. Harvey D., Tittley E., Massey R., Kitching T., Taylor A., Pike S.; Kay S., Lau E. and Nagai D., 2014,MNRAS, 441, 404.||en
|dc.relation.hasversion||Observing Dark Worlds: A crowdsourcing experiment for dark matter mapping. Harvey D., Kitching T., Noah-Vanhoucke J., Hamner B., Salimans T. and Pires A., 2014, Astronomy & Computing, 5, 35.||en
|dc.relation.hasversion||Origins of weak lensing systematics, and requirements on future instrumentation (or knowledge of instrumentation.) Massey, R., Hoekstra, H., Kitching, T., Rhodes, J., Cropper, M., Amiaux, J., Harvey, D., Mellier, Y., Meneghetti, M., Miller, L., Paulin- Henriksson, S., Pires, S., Scaramella, R., Schrabback, T., 2013, MNRAS, 429 661||en
|dc.subject||weak gravitational lensing||en
|dc.title||Measuring the self-interaction cross-section of dark matter with astronomical particle colliders||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en