The first stars formation in warm dark matter model

Liang Gao

National Observatories, China

Outline

• Why is WDM still interesting?

• 1st stars WDM

• 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.

Why warm dark matter?

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 beSeen 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 pictureFor high z star/galaxy formation.

• Thank you!