Theoretical work on Cosmology and Structure Formation
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Transcript of Theoretical work on Cosmology and Structure Formation
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Theoretical work on Cosmology and Structure
Formation
Massimo Ricotti
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Current PhD Students• Mia Bovill (Where are the Fossils of the first galaxies?)• KwangHo Park (simulations of accretion onto IMBH with
rad transfer)• Emil Polinsesky (Simulations of the Milky Way in CDM
and WDM)• Kari Helgason (First light from IR background fluctuations,
in collaboration with Alexander Kashlinsky)
• Available for 2nd year projects• But at the moment I cannot support additional RAs
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1. First structures in the Universe2. Galaxy formation in early universe
1. Radiative/chemical feedback2. Near field Cosmology3. Dark matter simulations
3. Reionization of the intergalactic medium1. Ly-alpha forest2. Sources of reionization: role of GCs and X-rays3. Primordial BHs and CMB
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The Missing Satellites
There should be thousands of dwarf satellites around the Milky Way.However, as of 2005 only about 30 satellites known in LG.Aquarius Simulation (Springel et al, 2008)
Klypin et al 1999, More et al 1999Figure credit: Grebel
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Less satellites if dark matter is warm
Imposing: Nsat(WMD simulation)≥Nsat(observed)-> we can set limits on warmness of DM and thus the mass of WDM particle
Results:If WDM is a thermal relicmwdm>2 keV
If WDM is a sterile neutrinoms>11 keV
This method is staring to become competitive and complementary with methods using Lyman-alpha forest (eg, Viel et al 2006, 2008) due to the recent discovery of many new MW satellites
Polisensky & Ricotti 2010
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Simulations of the first galaxies
Feedback-regulated galaxy formation
•1 Mpc box size•103 Msun mass res.•3D radiative transfer•Run ends at redshift of reionization
Ref: Ricotti, Gnedin & Shull 2002
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Properties of pre-reionization dwarfs
Dark
galaxies
Frac
tion
of c
osm
ic b
aryo
nsLuminous galaxies
Pre-reionizationdwarfs
At z=10
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Pre-reionization fossils and ultra-faint dSphs: a model prediction!
Ref: Ricotti & Gnedin 05, Bovill & Ricotti 09
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Hybrid Initial ConditionsThe final pre-reionization output is transformed in a 1 Mpc3 box of particles.
We duplicate this box, adding perturbations to account for density variations with l > 1 Mpc.
Each HR particle in the resulting N-body simulation represents a pre-reionization halo.
Unique IDs allow us to retrieve the stellar properties at z = 0.
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We now have z=0 halos which reproduce the faintest and smallest ultra-faints!
Yet undiscovered population
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Reionization feedback on dwarf galaxy formation
• The reionization feedback idea is valid but fails at z<2 if the halo is highly concentrated
• Minihalos virialized before reionization, that evolve to z=0 in the low-density IGM, have a late phase of gas accretion and possibly star formation
13.5 10 7 4 0AGE
SFR
13.5 10 7 4 0AGE
SFR
Do these objects exist?
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Late gas accretion onto mini-halos
Ref: Ricotti 2008
Zvir=10
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Sources of Reionization
1. Role of globular clusters2. X-ray pre-ionization: redshifted X-ray
background3. Accretion onto intermediate mass black holes
with radiation feedback (KwangHo Park)4. Primordial black holes
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Bondi accretion with radiation feedback
Gas density
Ionization fraction
100 Msolar IMBHPark & Ricotti 2010
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Accretion rate
See also Milosavljevic et al 2008
Park & Ricotti 2010
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Preliminary results Moving BH + Radiative Feedback
5/21/2010
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Primordial black holes
1. PBHs modify recombination history and produce spectral distortions and anisotropies
2. New upper limits on fpbh with WMAP33. PBHs promote formation of primordial H2 and
first stars 4. Ultracompact minihalos as MACHOs
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CMB anisotropies: WMAP3
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Constraints on fpbh from WMAP 3