The first stars formation in warm
dark matter model
Liang Gao
National Observatories, China
Outline
• Why is WDM still interesting?
• 1st stars WDM
Why warm dark matter?
• Small scale power spectrum of Universe is
poorly constrained, so why not?
• WDM is as good as CDM to interpret large
scale distribution of galaxies.
• There are some good physically motivated
dark matter particle candidates, e.g. sterile
neutrinos.
• Some open questions still remain in
Astronomy which may be explained better
with WDM.
1. Central density profile of dwarf galaxies.
2. Abundance of satellites in galaxies of the
Local Group.
Power spectrum constraints from observations
Power spectrum----CDM vs. WDM
Do properties of the first stars depend on
nature of dark matter particles?
•Yes.
•Location.
•Formation path.
•Possibly IMF.
Gao & Theuns, 2007, Science, 317, 1527
Structure formation is suppressed below dark
matter particle free streaming scale.
M_dm = 3 kev, M_fs ~ 3 x 10^8 solar mases
First structure in WDM
M_dm = 3 kev, M_fs ~ 3 x 10^8 solar mases
Structure of a filament
Linear analysis of stability of a
general collapsing filament
• A filament is unstable to axis-symmetric perturbations
of wavelength greater than about 2 times the filament
diameter, when the line mass
• When the line mass the filament greatly exceeds the
value for equilibrium, perturbations do not grow
much. The entire filament collapse toward the axis--
as long as the EOS remains isothermal
Larson 1985; Inutsuka & Miyama 1998
Iso-thermal collapse Non-Iso-thermal collapse
Inutsuka & Miyama 1998
Application to a primordial
filament 1.
• Two density scales where primordial gas collapse
may slow down.
• 1) n_h~10^4 cc where LTE level population are
achieved. Fragmentation mass scale ~100 solar
masses.
• 2) n_h>10^12 cc where gas become optical to H2
lines. Fragmentation mass scale <= 1-2 solar
masses.
Application to a primordial
filament 2.
• The filament is very uniform on large scales.
• There are powers no small scales in WDM.
• Seeds to trigger thermal - gravity has to
transfer larger scale power (induced by tidal
field) to small scales--implies fragmentation at
very high density
• A range of mass of stars formed in a huge
burst.
Conclusion: CDM vs WDM
CDM:
• massive, short-lived stars
WDM:
• both low and high-mass stars
• low-mass stars may exist today
• origin of peculiar abundances in MW stars (This explains existing two
HMP stars better ?).
• collapsing filament seed for super-massive black hole
Question: observability?
The huge high z star burst can
Seen with JWST and TMT?
Title: Searching for Dark Matter with X-ray Observations of Dwarf Spheroidal
Galaxies Speaker: Michael Loewenstein
Institute: Astrophysics Science Division, NASA/Goddard Space Flight Center,
USA Time: 4:00 pm, 27 May 2010,ThursdayVenue: seminar room, KIAA, Peking
University
• Abstract:The sterile neutrino is a plausible dark matter candidate that emits an
X-ray photon via radiative decay. I will present a progress report of our ongoing
dedicated search for dark matter using X-ray observations of dwarf spheroidal
galaxies. We have set new constraints on sterile neutrino parameters, and
uncovered evidence of a 5 keV sterile neutrino emission line in the Chandra
spectrum of the ultra-faint Willman 1 dwarf spheroid. The flux of this feature is
consistent with the hypothesis that neutrino oscillations in the early universe
produce all of the dark matter in the form of sterile neutrinos. I will evaluate the
strength of this evidence, summarize our strategy to test its significance through
future observations, and discuss the implications of a positive detection.
Confirmation would point the way to physics beyond the Standard Model, and
imply that future X-ray missions will map the dark matter distribution, including
the redshift.
Is it ture? If so, there will be quite a different picture
For high z star/galaxy formation.
• Thank you!