Formation of the First Stars Under Protostellar Feedback Athena Stacy First Stars IV 2012

Collaborators Volker Bromm (U.Texas) Andreas Pawlik (U. Texas) Thomas Greif (MPA) Avi Loeb (Harvard/CfA)

Dark Ages

Open Questions -What role did they play in reionization and metal enrichment? - What feedback did they exert on later star formation? (Pop III to Pop II transition) This depends on the Pop III IMF, SFR, and rotation rates… -What were their typical masses? -What was their typical multiplicity? - When will a Pop III protostar’s accretion become shut off by feedback ? or ??? or

I. Pop III Star Formation Without Feedback Stacy, Greif, & Bromm, 2010 MNRAS, 403, 45

??? Cosmological simulation: - Gadget (SPH + N-body) -initialized at z=100 according to  CDM model - followed formation of protostar (sink particle) and subsequent 5000 yr of accretion - m sph (gas) = M  - M res ~ 1.5N neigh m sph ~ 1 M  = minimum allowed Jeans mass

Initial Collapse IGM minihalosink 3-body reactions and H 2 formation (time)

Sink Particles  By using sink particles, we can continue following evolution of star-forming gas for thousands more years (~ 100 freefall times)! M sink = 1 M  n = cm -3 r acc ~ 50 AU ~ cm R  ~ cm  Density no longer evolved Accrete gas particles that fall within r acc of sink 50 AU

Pop III stars can form in multiples! Multiple stars form within a disk that has grown to ~ 40 M  (t acc = 5000 yrs) 5000 AU Density [cm -3 ]

Binary and Multiple Formation Toomre Fragmentation criterion: Q ~ 0.4 < 1 t cool < t rot and (Gammie 2001, Kratter et al. 2010, 2011) Multiple sinks form through disk fragmentation

Rapid Pop III Accretion Rates Sink B: M sink ~ t 0.25 dM/dt ~ t Sink A: M sink ~ t 0.5 dM/dt ~ t -0.5 B&L 2004 sink B sink A M final > 100 M 

II. Pop III Star Formation With Radiative Feedback Stacy, Greif, & Bromm, 2012, MNRAS, 422, 290

Protostellar Feedback Repeat previous cosmological simulation, but with updated H 2 cooling rates (Sobolev approximation) Model LW radiation and growth of surrounding HII region Also performed a comparison “no- feedback” simulation How will radiation alter the growth of the Pop III star?

-200 radial segments angular sements bins The I-front Tracker M * = M sink R * = ?

The Protostellar Model Hosokawa et al. 2010

Adiabatic accretion KH contraction ZAMS Adiabatic expansion KH contraction ZAMS

The Protostellar Model Adiabatic expansion KH contraction ZAMS Slow contraction model Simulation model M * =M sink

I-front breakout Ionization rate Mass infall rate M * = 15 M 

I-front Evolves in Morphology 1500 yr2500 yr4500 yr

Temperature Structure 2500 yr 3000 yr With feedback Sink potential well heating I-front Warm neutral bubble Without feedback 5000 yr 4000 yr 2500 yr

With Feedback * = main sink + = secondary sink

Feedback Slows Disk Growth No feedback With feedback Envelope = gas with n>10 8 cm -3

Without Feedback Density, x-y plane Density, x-z plane Temperature, x-y plane Temperature, x-z plane Box = 10,000 AU Disk disrupted by N-body dynamics

Reduced Accretion Rate With feedback M sink ~ t 0.09 Without feedback M sink ~ t nd largest sink (with feedback) M final ~ 30 M 

III. Pop III Formation Under Dark Matter Effects? Stacy, Pawlik, Bromm, & Loeb 2012, MNRAS, 421, 894

WIMP annihilation important for Pop III stars? ( Sky and Telescope, Gregg Dinderman) Can it heat SF gas, or replace/supplement nuclear fusion?

Pop III stars form in regions of high DM density

May lead to extremely massive and luminous Pop III stars (e.g., Freese et al. 2008, Spolyar et al. 2008, Iocco et. al 2008, Natarajan et al. 2009) -R * ~ 1 AU -T eff too low to ionize -Accretion unimpeded for long time a.k.a. “dark stars”

DM heating and capture rates Higher DM density  greater effect on gas and stars 1. DM heating  delayed protostellar contraction  prolonged accretion (M * reaches 10 5 M  ?) 2. DM capture by MS star  burn DM instead of hydrogen  prolonged stellar lifetime (to z=0?)

But will this work in a Pop III MULTIPLE system?

New DM Initialization 1. Begin simulation immediately after the first sink has formed 2. Align DM peak with main sink 3. Continue simulation for 20,000 yr How will these DM profiles evolve? Will density stay peaked?

Decline of DM Density on Stellar Disk Scales 10,000 yr 20,000 yr 10,000 yr 20,000 yr Minimum DM density for DM capture to support a star Sinks and DM density peak UNALIGNED

Rapid Decline of DM Effect on Gas and Stars Blue – DM capture rate within sinks (-> DM density) Black – DM heating rate within sinks (-> DM density 2 )

Pop III Mass Growth Relatively Unaffacted Sim A Sim B DM unrefined

Conclusions Range of Pop III masses is likely very broad. Multiple mechanisms, particularly disk fragmentation, will contribute to formation of low mass stars. Fragmentation and broad mass range likely to describe Pop III stars even under radiative feedback! Possibly massive binaries Pop III stars can likely reach tens of solar masses, but hundreds of solar masses may be harder (see also Susa and Hosokawa’s talks)  Maybe explains why PISN signature has not been observed (requires 140M  < M * < 260M  ) Pop III multiplicity will strongly mitigate effects of DM annihilation - ‘dark stars’ unlikely (see also Smith’s poster and Iocco’s talk) Growing understanding of Pop III stars will ultimately increase physical realism of models of later star and galaxy formation

Questions?

THE END Thank you!