dc.contributor |
Háskóli Íslands |
dc.contributor |
University of Iceland |
dc.contributor.advisor |
Jesús Zavala Franco |
dc.contributor.author |
Burger, Jan David |
dc.date.accessioned |
2021-08-20T15:15:25Z |
dc.date.available |
2021-08-20T15:15:25Z |
dc.date.issued |
2021 |
dc.identifier.citation |
Jan David Burger, 2021, Stellar orbits in adiabatically and impulsively evolving dark matter dominated potentials, PhD dissertation, Faculty of Physical Sciences, University of Iceland, 285 pp. |
dc.identifier.isbn |
78-9935-9614-2-6 |
dc.identifier.uri |
https://hdl.handle.net/20.500.11815/2654 |
dc.description.abstract |
In the ΛCDM concordance model cold and collision-less dark matter (CDM) accounts
for about four fifths of the Universe’s total matter content, while visible baryonic matter
makes up the final fifth. The ΛCDM model successfully describes how large scale
structure forms from tiny density fluctuations in the early Universe, explaining the
growth of dark matter (DM) overdensities and their eventual collapse into gravitation-
ally self-bound objects called haloes which host the visible galaxies. The most enduring
challenges to the ΛCDM paradigm arise on the scale of dwarf galaxies whose internal
kinematics are seemingly at odds with the radial density profiles of the corresponding
DM haloes predicted by CDM N-body simulations. While the evidence for such mis-
matches remains controversial, several mechanisms have been proposed to reconcile
the success of ΛCDM on large scales with these observations on smaller scales. Typ-
ically, such mechanisms rely on non-gravitational effects to redistribute mass within,
and thus alter the gravitational potential of, DM haloes. Depending on the specific
mechanism, this mass redistribution occurs on timescales which are either longer or
shorter than the typical dynamical timescales of stars in dwarf galaxies. In this thesis, I
show that stars can be used as kinematic tracers to differentiate between adiabatically,
i.e., slowly evolving, and impulsively, i.e., fast evolving potentials. In adiabatically
evolving potentials, the actions of kinematic tracers are conserved. For moderately fast
evolving spherical potentials, I show that the evolution of radial actions is perturbative
and oscillatory. In this regime, the evolution of radial action distributions of tracers is
well described by a diffusion equation. The evolution of a tracer’s radial action becomes
non-perturbative as the rate at which the potential changes becomes large compared
to the tracer’s radial period. An impulsive change in the gravitational potential, under
which actions are not conserved, changes the energy of kinematic tracers by an amount
that depends on their orbital phase. Using controlled N-body simulations, I demon-
strate that as a consequence of the latter, shell-like signatures related to phase mixing
emerge in the phase space of kinematic tracers whose orbits where characterized by
similar integrals of motion prior to the change in the potential. Such orbital families are
reasonably approximated by sets of stars with similar ages and metallicites. Ongoing
phase mixing in orbital families within dwarf galaxies with slow-rising rotation curves
would indicate the presence of strong and impulsive supernova feedback which may
have converted the central cusps of the dwarfs’ host haloes into cores. Using a suite of
hydrodynamic simulations of an isolated dwarf, I find that the kinematic properties of
stars and gas differ in many ways between galaxies whose host haloes have an impulsive
or an adiabatic core formation history. The complete absence of shell-like signatures
of phase mixing in orbital families would be a strong indication that cores are likely
formed adiabatically, for example through self-interactions between the DM particles. |
dc.description.abstract |
Í hinu samræmda ΛCDM líkani er um fimmtungur alls efnis sýnilegar þungeindir og fjórir fimmtu hlutar hulduefni. Líkanið gefur góða lýsingu á því hvernig stórgerð alheimsins
er til komin vegna lítilla þéttleikasveiflna í árdaga og hvernig yfirþéttleiki hulduefnis
þróast yfir í þyngdarbundna hjúpa sem hýsa sýnilegar vetrarbrautir. Sterkasta áskorun
líkansins kemur fram á skala dvergvetrarbrauta en gangfræði þeirra virðist stangast á
við þéttleikaprófíl hulduefnishjúpanna sem spáð er í fjölagna hermireikningum. Þó
vísbendingarnar um þetta misræmi séu umdeildar eru nokkrar mögulegar skýringar á því
hvernig á þessu getur staðið. Oft byggjast þessar skýringar á þyngdarverkunarlausum
hrifum sem breyta massadreifingu hulduefnishjúpsins og þar með einnig þyngdarmætti
hans. Það fer svo eftir eðli hrifanna hvort massadreifingin breytist á tímaskala sem er
styttri eða lengri en dæmigerður hreyfifræðilegur tími stjarna í dvergvetrarbrautum.
Í þessari ritgerð sýni ég að nota má stjörnur sem hreyfifræðilega spora (tracer)
til að greina á milli annars vegar óverminna (hægfara) breytinga á mættinu og hins
vegar snöggra breytinga á því. Í óvermnum breytingum er verkun hreyfifræðilegu
sporanna varðveitt. Þá sýni ég að í kúlusamhverfu mætti sem þróast miðlungi hratt er
radíalverkunin bæði truflin (perturbative) og sveiflukennd og að lýsa má þróun dreifingar radíalverkunarinnar með sveimjöfnu. Tímaþróun radíalverkunar sporanna verður
ótruflin þegar tímaþróun mættisbreytinganna verður hraðari en sem nemur útþáttarlotu
(radial period) sporanna. Við snögga breytingu í þyngdarmættinu, þar sem verkunin
er ekki varðveitt, breytist orka sporanna um stærð sem er háð brautarfasa þeirra. Með
stýrðri hermun fjölagnakerfa sýni ég að afleiðing hins síðarnefnda er að í fasarúmi
sporanna koma fram merki um hvelamyndun í brautum þeirra. Þeim má lýsa allvel
með fjölskyldum stjarna af svipuðum aldri og málminnihaldi. Fasablöndun fjölskyldna
brauta stjarna í dvergvetrarbrautum með hægt vaxandi snúningshraðarit er vísbending
um sterka og snögga sprengistjörnusvörun sem gæti hafa breytt þéttleikaprófíl hjúps
dvergvetrarbrautarinnar. Með hermun einangraðrar dvergvetrarbrautar sýni ég að hreyfifræði gass og stjarna er ólík eftir því hvort kjarni hjúpsins hefur þróast óvermið eða
snögglega. Ef engin merki er að finna um fasablöndnun brautarfjölskyldna er það sterk
vísbending um að hjúpurinn hafi þróast á óverminn hátt, t.d. með eiginvíxlverkun á
milli einda hulduefnisins. |
dc.description.sponsorship |
This work was supported by a Grant of Excellence from the Icelandic Research
Fund (grant number 173929) |
dc.format.extent |
301 pages |
dc.language.iso |
en |
dc.publisher |
University of Iceland, School of Engineering and Natural Sciences, Faculty of Physical Sciences |
dc.rights |
info:eu-repo/semantics/openAccess |
dc.subject |
Dark matter |
dc.subject |
Stellar dynamics |
dc.subject |
Galaxy formation and evolution |
dc.subject |
Astronomy |
dc.subject |
Astrophysics |
dc.subject |
Vetrarbrautin |
dc.subject |
Stjarneðlisfræði |
dc.subject |
Stjörnufræði |
dc.subject |
Doktorsritgerðir |
dc.title |
Stellar orbits in adiabatically and impulsively evolving dark matter dominated potentials |
dc.type |
info:eu-repo/semantics/doctoralThesis |
dc.contributor.department |
Raunvísindadeild (HÍ) |
dc.contributor.department |
Faculty of Physical Sciences (UI) |
dc.contributor.school |
Verkfræði- og náttúruvísindasvið (HÍ) |
dc.contributor.school |
School of Engineering and Natural Sciences (UI) |