Primordial Supernovae and the Assembly of the First Galaxies

Daniel Whalen Bob Van VeelenX-2, LANL Utrecht

Michael Norman Brian O’SheaUCSD T-6, LANL

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arXiv:0801.3698

Current Paradigms for the Formation of the First Galaxies

assemble a few stars at a time as individual small dark matter halos, each hosting a solitary star, consolidate by mergers

form stars consecutively, each in the relic H II region of its progenitor (O’Shea, Abel, Whalen & Norman 2005, Yoshida, et al 2007)

in some cases, form stars in both the metals and H II regions of their predecessors (Greif, et al 2007, Wise & Abel 2007)

2nd Star Formation in Relic H II Regions

• fossil H II regions of the first stars cool out of equilibrium, and their temperatures fall faster than they recombine

• H2 and HD rapidly form in such circumstances, causing primordial gas to condense and fragment into new stars

• If HD cooling dominates, gas temperatures fall to the CMB, causing it to fragment on smaller mass scales than the parent star

• this process results in at most a few new stars forming in the halo of the progenitor on timescales less than merger times (20 - 30 Myr at z ~ 20)

Yoshida, Oh, Kitayama & Hernquist 2007

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Greif, et al 2007 Wise & Abel 2008

• primordial 1st generation stars explode in their H II regions

• in these numerical scenarios, metals are preferentially expelled into voids of low density in which star formation cannot occur

• protogalaxies are again built up a few stars at a time and are contaminated gradually as inflow and mergers carry metals back into halos, typically on timescales of 50 - 100 Myr

• metallicities greater than 10-3.5 solar can result in a direct rollover to a low mass 2nd generation

Current numerical models fail to properly resolve primordial H II region and supernova dynamics, both of which may lead to a prompt second generation of stars

Consequently, the first galaxies may have formed with far greater numbers of stars and different metallicities than now supposed

~ 200 pc

CosmologicalHalo z ~ 20

Properties of the First Stars

• thought to be very massive (30 - 500 solar masses) due to inefficient H2 cooling

• form in isolation (one per halo)

• Tsurface ~ 100,000 K

• extremely luminous sources of ionizing and LW photons (> 1050 photons s-1)

• 2 - 3 Myr lifetimes

• new results extend Pop III lower mass range down to 15 solar masses (O’Shea & Norman 2007, ApJ, 654, 66)

Transformation of the Halo

ZAMS End of Main Sequence

Primordial Ionization Front Instabilities

Final Fates of the First Stars

Heger &Woosley2002

Primordial Supernova in Cosmological Simulations: Neutral Halos

• temperatures skyrocket to 109 K at the center of the halo

• the hot, ionized, dense center emits intense bremsstrahlung x-rays • the core radiates away the energy of the blast before it can sweep up its own mass in the halo

They Fizzle!

Yoshida & Kitayama 2005, ApJ, 630, 675

Recipe for an Accurate PrimordialSupernova

• initialize blast with kinetic rather than thermal energy

• couple primordial chemistry to hydrodynamics with adaptive hierarchical timesteps

• implement metals and metal-line cooling

• use moving Eulerian grid to resolve flows from 0.0005 pc to 1 kpc

• include the dark matter

potential of the halo

Truelove & McKee 1999, ApJ, 120, 299

ZEUS-MP 1D Primordial Supernova:9 Models

• Halos: 6.9 x 105, 2.1 x 106, and 1.2 x 107 solar masses

• Stars: 25, 40, and 200 solar masses (Type II, hypernova, and pair-instability supernovae)

• Stage 1: illuminate each halo for the lifetime of its star

• Stage 2: set off the blast and evolve the remnant for 7 Myr

4 SN Remnant Stagesin H II Regions

• t < 10 yr: free-expansion shock

• 30 yr < t < 2400 yr: reverse shock

• 19.8 kyr < t < 420 kyr: collision with shell / radiative phase

• t > 2 Myr: dispersal of the halo

Reverse Shock Collision with the Shell

4 SN Remnant Stagesin Neutral Halos

• t < 1 yr: free-expansion shock

• t < 20 yr: early radiative phase

• 100 yr < t < 5000 yr: late radiative phase

• t > 1 Myr: fallback

Late Radiative Phase Fallback

Enormous, Episodic Infall Rates During Fallback

ObservationalSignatures ofPrimordial Supernovae

Halo Destruction Efficiency

Conclusions

• if a primordial star dies in a supernova, it will destroy any cosmological halo < 107 solar masses

• supernovae in neutral halos do not fizzle--they seriously damage but do not destroy the halo

• primordial SN in H II regions may trigger a second, prompt generation of low-mass stars that are unbound from the halo

• blasts in neutral halos result in violent fallback, potentially fueling the growth of SMBH seeds and forming a cluster of low-mass stars

2D Metal Mixing Due to Radiative Cooling

Thanks!

Primordial Supernova inCosmological Simulations: H II Regions

• the remnant collides with the dense H II region shell and later grows to half the radius of the H II region

• metals preferentially permeate voids

• neither metals nor gas return to the halo in less than a merger time (~ 50 - 100 Myr)

Star Formation is Postponed!

Bromm, Yoshida & Hernquist 2003, ApJ, 596, 195LGrief, Johnson & Bromm 2007, ApJ, 670, 1