Simulations of Reionization-Epoch Galaxies

1. Simulations of Reionization-Epoch Galaxies Romeel Davé (Arizona) Kristian Finlator, Ben D. Oppenheimer

2. Movie by N. Gnedin z~7 arc in Abell 2218 Kneib et al 2004 Galaxies at z>6: Why? • Responsible for reionizing the universe. • Test early galaxy formation models. • Now observed! • What are their physical properties? • What constraints do they place on models?

3. 3 Mpc/h comoving Cosmological Hydro Simulations • Gadget-2 (PM-Tree-eSPH), with new momentum-driven wind models + metal-line cooling (no H2). • Reproduces observed IGM metals at z~2-5 (Oppenheimer & RD 06) • 2x2563 runs, LCDM, [8,16,32,64]h-1Mpc, various outflows. • No radiative transfer, uniform HM01 (QG01) reionizes @ z~9. • Feedback cycle tracked self-consistently; geometry critical. Movie by B. Oppenheimer

4. GOODS B-dropouts Bouwens et al 06 RD, Finlator, Oppenheimer 06 Rest-UV Luminosity Functions • nw: no winds; cw: “constant” winds, vw=484 km/s (Springel & Hernquist 2003); mzw/vzw: momentum-driven winds, vws (from local starbursts; Martin 2005). • Matches rest-UV LF at z~4-6; steep slope @ faint-end! • Overcooling @ z~6: Large suppression of SF needed at early times, across all masses.

5. Stellar Mass buildup ~JWST depth • Despite large suppression, stellar mass builds up quickly. • At z=7, space density of M*>1010M objects ~ SDSS LRG’s today. • Halos masses ~100M*~109-1012M Atomic line cooling dominates. • Tight M*-SFR relation driven by cold-mode accretion (Keres etal 05). RD, Finlator, Oppenheimer 06

6. Zahn et al 2006 Galaxies Self-Reionize Early • Lots of SF  lots of ionizing photons • Stromgren sphere overlap as a function of M*: Percolation at z»9 for M*<109M. • Combined with large vcirc  Rad Xfer not critical for studying 6<z<9 galaxies. RD, Finlator, Oppenheimer 06

7. Galaxies Self-Enrich Quickly • …despite strong outflows that enrich IGM. • Typical ~0.1-0.3Z @ z~6, very little evolution with z. • M*-Z rel’n evolves slowly to z~2, agrees with Erb etal 06. • Very little “metal free” SF (Z<10-3Z); bulk of IMF normal. Points: Erb etal 06 z~2 Line: SDSS z~0 RD, Finlator, Oppenheimer 06

8. Case Study: Abell 2218 KESR • z~6.7 galaxy well-fit by simulated, independent of outflows/cosmology. • This galaxy is typical: M* and SFR fall exactly on simulation’s tight M*-SFR correlation. • Star formation history best characterized by steady rise; NOT constant, decaying, or single-burst; yet all models fit with 2<1. Finlator, RD, Oppenheimer 06

9. SPOC: Physical Constraints from Simulated Galaxies • SPOC: Bayesian engine to constrain physical parameters from photometric data by comparison with simulated sample. • Provides tighter constraints than “toy model” SFHs because simulated SFHs are ~self-similar. • Also tests model: If “prior” is wrong, no good fit obtained! Finlator, RD, Oppenheimer 06

10. 2~3 2~8 Constraining z~6 Galaxies • 6 observed objects have M*~109-10 M, SFR~2-50 M/yr. • All well-fit by simulated galaxies except GLARE#3001; this one poorly fit by ALL models, seems “bursty”. • SPOC identifies outlier objects that critically test models. Finlator, RD, Oppenheimer 06

11. Summary • Galaxies at 6<z<9 are fundamentally similar to lower-z systems: Massive, SFRM*, enriched to >~0.1Z, live in reionized regions by z~9. • Simulations can match observed luminosity function if feedback heavily suppresses star formation by z~6. • Mass-metallicity relation evolves very slowly, and even at z~9 there is little Population III star formation. • Individual observed galaxies are straightforwardly accommodated in simulations, and in turn models be used to constrain physical parameters using SPOC.