Outflows and Chemical Enrichment in the First Galaxies Jeremy Ritter Chalence Safranek-Shrader, Miloš Milosavljević, Volker Bromm

The First Galaxies Ancient stellar systems containing dark matter Primitive chemical enrichment history: contributing nucleosynthetic sources not homogenized Not directly observable before James Webb Space Telescope Surviving relics in the local universe: Milky Way’s satellites (“near-field cosmology”)

Alan W. McConnachie 2012 The Astronomical Journal 144 4

Segue 1: M. Geha (DEIMOS)

Ultra Faint Dwarfs Could they be examples of the first galaxies? – The lowest luminosity dark matter dominated stellar systems known Why are the mass to light ratios so large? – Dark matter-stellar mass ratio ~ 1000 – Compare to the cosmological ratio Ω dm /Ω b ~ 5 How did they lose their baryons? – Ram pressure stripping? – Supernova explosions can unbind gas

Evan N. Kirby et al ApJ

UFD Chemical Evolution History Low metallicities −2.5 < [Fe/H] < −1.5 Significant metallicity spread σ [Fe/H] ~ 0.5 – Merging of chemically heterogeneous progenitors? – Inhomogeneous local enrichment? Metallicity decreases with luminosity – Is metallicity an accurate cosmic clock, as normally assumed?

Luis C. Vargas et al ApJ

UFD Chemical Evolution History Enhanced α-element abundances [α/Fe] > 0 α-enhancement declines above a critical [Fe/H] – Signature of SN Ia enrichment at very low metallicities Segue 1 – [α/Fe] ~ 0.5, average [Fe/H] ~ −2.5 – pure core collapse chemistry: no pair-instability, SN Ia, or AGB (s-process) signatures.

Frebel and Bromm 2012 ApJ Frebel et al ApJ

Marla Geha et al ApJ

Safranek-Shrader et al. MNRAS (2014) 440 (1): L76-L80.

Ritter et al. 2014, in prep.

Research Collaborators Volker Bromm Miloš Milosavljević Alan SluderChalence Safranek-Shrader

Open Research Questions If Pop III stars had masses above 10 M , could they produce the UFD core-collapse signature? How far from a minihalo is ejecta dispersed by supernovae with different mass and energy? How long does it take for ejecta to fall back and enrich gas that can cool and collapse? What is the metallicity structure in cold gas enriched by Pop III core-collapse supernovae?

Methodology 3d cosmological simulation of dark matter and baryons – FLASH AMR code embedded with N-body dark matter particle integration and multi-grid gravity solver – Non-equilibrium atomic and molecular chemistry Reproduce the thermodynamic response of ionized gas to photoheating in an H II region around PopIII stars – 3d radiative transfer calculation along 3072 radial pixels Insert a kinetic blastwave at extremely high resolution and follow the evolution of gas and ejecta hydrodynamics for several tens of millions of years

Test of H II Region Photoheating 200 Msun 2.2 Myr 2.6 × ionizing photons per second Flat inner profile approaches 0.1 cm -3 Bounded by a dense shell out to 100 pc Spherically averaged radial density profile

Test of SN Remnant Hydrodynamics M ejecta = 40 M  E kinetic = 6×10 51 ergs M Z / M ejecta = 0.3 (α-enhanced composition)

8.5 Myr after a erg supernova with 40 M  of ejecta Single Core Collapse Supernova Circle encloses R vir = 200 pc of a 10 6 M  minihalo

Ejecta Fallback Less than 50% of metal ejecta has enough momentum to leave the virial radius after 40 Myr

Before SN, M halo = 10 6 M  40 Myr after SN, M halo = 4×10 6 M  Gas thermodynamic profile recovers after only a few times 10 Myr

Sustained inflow of mass after 5 Myr – Total mass inflow rate reaches M  yr -1 – Average metallicity Z ≈ Z  – Highly inhomogeneous Baryons Metals

baryon density slice + ejecta particles in projection 360 pc1100 pc Inhomogeneous Enrichment

Challenges for Resolving Metallicity Inhomogeneity in Metal Enriched Star Formation Numerical diffusion of passive mass scalars inherent to AMR simulations – Particles trace the ejecta fluid to show where metals can travel Instabilities at large and small scale in blastwaves are difficult to resolve simultaneously – AMR grid is dynamically refined to ensure the Jean’s length and hydrodynamic instabilities are resolved – New SN remnants can be inserted by zooming in to extremely high resolution while maintaining previous remnants at moderately high resolution

Multiple Supernovae in a Minihalo Protostellar disk fragmentation produces Pop III stars in small, compact clusters Sample a Pop III initial mass function to compute delay times of consecutive supernovae Pop III stars of different masses should have distinct nucleosynthetic signatures (though the detailed yields are not currently known) Time separation of supernova events opens the possibility of complexity in metal dispersal

Multiple Supernovae: Methodology Pop III star cluster sampled from a flat IMF – Masses: 80, 63, 50, 40, 32, 25, and 20 M  – Lifetimes: 3.1, 3.25, 3.6, 4.1, 4.9, 6.1, and 7.7 Myr – Total ionizing photon emission 2.2 × photon/s Kinetic blastwaves all inserted with ergs – Initial radius at high density 0.6 pc (cell size 0.02 pc) and at low density 2.9 pc (cell size 0.09 pc) much less than the radius of equivalent mass Track the ejecta from each supernova separately using individually tagged passive tracer particles

Source Heterogeneity: Tracing Individual Ejecta Exterior viewCross sectional view (kpc)

Limitations of the Methodology I-front kinematics are not accurately reproduced – Large scale thermodynamic response to photoheating and the failure to destroy the filaments are consistent with other simulations and literature Thermal conduction in dense, superheated gas – Cold gas ablated from the surface is diluted by hot gas

Summary of Preliminary Findings Ejecta have reached distances greater than 1.5 kpc after 72 Myr Mass loading by dense gas in cosmic filaments causes ejecta to lose momentum and fall back Metal ejecta remains clumpy and unmixed Streams from the filaments bring primordial gas to the center of the halo which has not yet been significantly enriched after 72 Myr

Further Analysis Needed Continue the simulation until enriched gas is able to cool and recollapse to high density Analyze the metallicity distribution of metal- enriched cold gas Discern the individual contributions to the outflow and fallback from each supernovae Fork a new simulation to track the large scale, long-term evolution of the outflow

Future Projects Collaborate to simulate the formation of metal- enriched, second generation stars from cosmological initial conditions – Simulate the explosion and inhomogeneous enrichment by a 60 M  star in a minihalo until cold gas in the fallback has reached extremely high density 10 7 cm -3 – Cut out a portion of the cosmological box containing the metal enriched halo and simulate the formation of individual protostellar cores (Safranek-Shrader) – Compare the metallicity and mass distribution of simulated protostars to the known very metal-poor stars

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Scalar Transport Eulerian: diffusion grows a spurious pseudo-exponential tail. If the thermodynamic evolution is sensitive to Z ~ 10 −3 Z  ~ 10 −5 or smaller with dust, a spuriously large gas mass can cool. Turbulence assisted mixing requires several turbulent eddy crossing times. If turbulence is weak, the metals from SN ejecta and the unpolluted gas could remain well separated on small scales.