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Radiative and Chemical Feedback by the First Stars. Daniel Whalen McWilliams Fellow Carnegie Mellon University. My Collaborators. Joe Smidt (UC Irvine) Thomas McConkie (BYU) Brian O’Shea (MSU) Mike Norman (UCSD) Rob Hueckstaedt (LANL). Numerical Simulations of Local Radiative

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slide1

Radiative and Chemical Feedback

by the First Stars

Daniel Whalen

McWilliams Fellow

Carnegie Mellon University

slide2

My Collaborators

  • Joe Smidt (UC Irvine)
  • Thomas McConkie (BYU)
  • Brian O’Shea (MSU)
  • Mike Norman (UCSD)
  • Rob Hueckstaedt (LANL)
slide3

Numerical Simulations of Local Radiative

Feedback on Early Star Formation

Uniform Ionizing/LW

Backgrounds

Rad Hydro Models

of Single Halos

  • Machacek, Bryan & Abel 2001,
  • MNRAS, 548, 509
  • Machacek, Bryan & Abel 2003,
  • MNRAS, 338, 273
  • O’Shea, Abel, Whalen & Norman
  • 2005, ApJL, 628, 5
  • Mesinger, Bryan & Haiman 2006,
  • ApJ, 648, 835
  • Mesinger, Bryan & Haiman 2009,
  • MNRAS, 399, 1650
  • Susa & Umemura 2006,
  • Ahn & Shapiro 2007, MNRAS,
  • 375, 881
  • Whalen et al 2008, ApJ, 679,
  • 925
  • Whalen, Hueckstaedt &
  • McConkie 2010, ApJ 712,101
slide4

The Universe

at Redshift 20

128 kpc comoving

slide5

ZEUS-MP Reactive Flow

Radiation Hydrodynamics Code

  • massively-parallel (MPI) Eulerian hydrocode with 1-, 2-,
  • or 3D cartesian, cylindrical, or spherical meshes
  • 9-species primordial H/He gas network coupled to photon
  • conserving multifrequency UV transfer
  • Poisson solver for gas self-gravity
  • includes the dark matter potential of cosmological halos,
  • which remains frozen for the duration of our calculations
slide6

40 energy bins < 13.6 eV, 80 bins from 13.6 eV to 90 eV

  • self-shielding functions of DB 96 corrected for thermal
  • Doppler broadening are used to compute H2 photo-
  • dissociation
slide7

Adaptive Subcycling

  • three characteristic timescales emerge when one couples
  • radiation to chemistry and hydrodynamics:
  • the trick is to solve each process on its own timescale without
  • holding the entire algorithm hostage to the shortest time step
  • procedure:
  • (1) while holding densities and velocities fixed, evolve
  • reaction network and gas energy on global min of tchem
  • and th/c until the global min of th/c is crossed
  • (2) perform density and velocity updates (the hydro) every
  • th/c
slide8

Parameter Space of Surveyed Halos

  • We sample consecutive evolutionary stages of a single
  • 1.35 x 105 solar mass halo rather than the entire cluster
  • at a single redshift
  • Since halos in the cluster tend to be coeval, exposing
  • just one at several central densities spans the range of
  • feedback better than a few at roughly the same density
  • We chose this halo mass because it is the smallest in
  • which we expect star formation, so feedback would be
  • less prominent than in a more massive halo
slide9

Spherically-Averaged Enzo AMR Code Halo Radial Density and

Velocity Profiles (O’Shea & Norman 2007b)

z = 23.9, 17.7, 15.6 and 15.0

slide16

I-Front Structure

monoenergetic:

20 - 30 mfp

e, T

105 K blackbody:

e, T

T-Front

quasar:

e, T

secondary ionizations by photoelectrons

slide19

25 Msol

40 Msol

60 Msol

Whalen et al 2008,

ApJ, 682, 49

Whalen et al 2010,

ApJ, 712, 101

80 Msol

120 Msol

slide20

Local Radiative Feedback

  • due to coeval nature of halos within the cluster, feedback
  • tends to be positive or neutral
  • halos with nc > 100 cm-3 will survive photoevaporation
  • and host star formation (accelerated in many instances)
  • feedback sign is better parameterized by central halo
  • density than halo mass
  • radiation drives chemistry that is key to the hydrodynamics
  • of the halo -- multifrequency transfer is a must
  • these results are mostly independent of the spectrum of
  • the illuminating star--more LW photons don’t make much
  • difference
slide21

Nucleosynthetic Forensics

of the First Stars

Daniel Whalen

Candace Joggerst

2010, ApJ, 709, 11

2011, ApJ, 728, 129

slide22

Our Collaborators

  • Ann Almgren (LBNL)
  • John Bell (LBNL)
  • Alexander Heger (University of Minnesota)
  • Stan Woosley (UC Santa Cruz)
slide23

The Primordial IMF Remains Unconstrained

Numerical simulations, although proceeding from well-posed initial conditions, lack the physics to model star formation up to the main sequence (and likely diverge from reality well before)

Direct observation of primordial supernovae, in concert with gravitational lensing, may be possible with JWST (Kasen & Woosley 2010; Whalen et al 2011a,b,c, in prep)

Stellar archaeology, in which we search for the nucleosynthetic imprint of Pop III stars on low-mass

subsequent generations that survive today, is our best

bet for indirectly constraining the primordial IMF

slide24

Final Fates of the First Stars

Heger & Woosley 2002, ApJ 567, 532

slide25

Stellar Archaeology: EMP and HMP Stars

  • Hyper Metal-Poor (HMP) Stars:
  • -5 < [Fe/H] < -4  thought to be enriched by one or
  • a few SNe
  • Extremely Metal-Poor (EMP) Stars:
  • -4 < [Fe/H] <-3  thought to be enriched by an entire
  • population of SNe because of the
  • small scatter in their chemical
  • abundances
slide26

No PISN?

  • original non-rotating stellar
  • evolution models predict a
  • strong ‘odd-even’ nucleosynthetic
  • signature in PISN element
  • production
  • to date, this effect has not been
  • found in any of the EMP/HMP
  • surveys
  • intriguing, but not conclusive,
  • evidence that Pop III stars had
  • lower initial masses than suggested
  • by simulation
  • this has directed explosion models
  • towards lower-mass stars

Heger & Woosley 2002

slide27

2D Rotating Progenitor Pop III Explosion

Models

  • progenitors evolved in the 1D KEPLER
  • stellar evolution code, exploded, and then
  • followed to the end of nucleosynthetic burn
  • (~ 100 sec)
  • KEPLER profiles then mapped into the new
  • CASTRO AMR code and then evolved in 2D
  • out to shock breakout from the star
  • 2 rotation rates, 3 explosion energies, 3
  • masses, and 2 metallicities, for a total of 36
  • models
  • self-gravity of the gas plus the gravity of the
  • compact remnant (the latter is crucial for
  • capturing fallback)

CASTRO Code (Almgren et al 2009)

slide28

Mixing & Fallback vs Mass,

  • Eex, and Metallicity
  • mixing falls and fallback rises
  • with increasing mass
  • mixing increases and fallback
  • decreases with rising Eex
  • mixing and fallback rise with
  • metallicity
slide31

Mixing in 150 –

250 Msol Pop III

PI SNe

Joggerst & Whalen 2011,

ApJ, 728, 129

slide32

The Nucleosynthetic Imprint of 15 – 40 Msol Pop III Stars on the First Generations

  • 15 – 40 M rotating Pop III progenitors are a good fit to one of the
  • HMP chemical abundances but not the other two
  • an IMF-average of the chemical yields of our zero-metallicity models
  • provides a good fit to the abundances Cayrel et al 2004 and Lai et al
  • 2008 measured in their EMP star surveys
  • since EMP stars are imprinted by well-established populations of
  • SNe, they are a better metric of primordial SN progenitors
  • direct comparison of nucleosynthetic yields from numerical models
  • to the abundances of MP stars is problematic—intervening
  • hydrodynamical processes complicate elemental uptake into new
  • stars
  • newly completed surveys (like SEGUE-II) will greatly expand our sample
  • of metal-poor stars and yield great insights into the primordial IMF