The HII Region of a Primordial Star
Abstract
The concordance model of cosmology and structure formation leads to the formation of isolated massive stars at very high redshifts in dark matter dominated halos of 105 to 106 M⊙. These stars photo-ionize their host primordial molecular clouds and expelling all the baryons from their halos. When the stars die a relic HII region is formed within which large amounts of molecular hydrogen is formed which will allow the gas to cool efficiently when gravity assembles it into larger dark matter halos. The filaments within which the first star hosting halo forms are largely shielded. It is along these filaments that gas continues to stream into the halo that hosted the primordial star. We present the first fully three dimensional cosmological radiation hydrodynamical simulations that self-consistently follow all these effects. Using a novel adaptive ray casting technique the time dependent radiative transfer around point sources is solved. This approach, is fast enough so that radiation transport, kinetic rate equations and hydrodynamics can be solved coupled in self-consistent. It retains the time derivative of the transfer equation and is explicitly photon conserving. This method is integrated with the cosmological adaptive mesh refinement code enzo and runs on distributed and shared memory parallel architectures. Where applicable the three dimensional calculations confirm expectations from earlier one dimensional results but also illustrate the multi-fold complexities of HII regions reminiscent of observations of local star forming regions. The simulations illustrate the circumstellar environments of the first supernovae and putative early gamma ray bursts. Albeit marginally resolved, ionization front instabilities create small scale structure reminiscent of nearby star forming regions. Relic primordial HII regions significantly affect subsequent structure formation.
  1. ‣    Abstract
  2. ‣    Movies
  3. ‣    Images
Tom Abel — Stanford University / KIPAC
John Wise — Stanford University / KIPAC
Greg Bryan — Columbia University
 
Images
astro-ph/0606019
High Resolution Figure 2
Projections of gas density (top) and temperature (bottom).  They are ~3 proper kiloparsecs across, and the insets have the same colorscale and are 150 pc across.  The columns (left to right) correspond to the star’s birth, 1 million years after, 2.7 million years after (star’s death), and 8 million years after.
 
 
 
 
 
 
 
 
A similar figure for electron and molecular hydrogen fractions (not included in published paper).  The middle bottom projections are enhanced by a factor of 10^4.
Movies (Quicktime)
Density
Projections of density squared. We choose this weighting to highlight overdensities.  All scales below are the side length of the movie and are proper distances.
 
1.    150 pc     [ x y z ]
2.    750 pc     [ x y z ]
3.    1.5 kpc    [ x y z ]
4.    3 kpc       [ x y z ]
Temperature
Projections of temperature weighted by density squared. All scales below are the side length of the movie and are proper distances.
 
1.    150 pc     [ x y z ]
2.    750 pc     [ x y z ]
3.    1.5 kpc    [ x y z ]
4.    3 kpc       [ x y z ]
Figure 1
Here are radial profiles of (A) molecular hydrogen and electron fractions, (B) temperature, (C) gas density, and (D) radial velocity as measured from the primordial star for the star’s birth, 0.1, 1, 2.7 (star’s death), and 8 Myr after.
Contact:
Tom Abel -- tabel {at} stanford {dot} edu
John Wise -- jwise {at} slac {dot} stanford {dot} edu
Greg Bryan -- gbryan {at} astro {dot} columbia {dot} edu
Merger History
Projections of density squared across 31 comoving kpc for the previous 50 million years (z = 25.7→20.4).  The colorscale is identical to the other density projections.
 
Projection axis: [ x y z ]