Unraveling the Galaxy to Find the First Stars: Nucleosynthesis at Z = 0... Jason Tumlinson Yale Center for Astronomy and Astrophysics... or, how I learned to stop worrying and love low-mass stars.

An Important Distinction Nucleosynthesis = Creation of the elements by coupled nuclear reactions in stars. Chemical Evolution = Processing in ISM, and incorporation into new stars. These are closely coupled by the metallicity- dependent details of stars - rotation, mass loss, post-MS evolution, supernovae, etc. Understand stellar evolution at low Z & Z = 0; Constrain the IMF in primordial gas; Reconstruct the early mass assembly of galaxies; Understand the origin of important and rare elements. Four ingredients, four motivations:

Rich New Data, Puzzling New Patterns Beers & Christlieb (2005) ARA&A VLT data - Cayrel et al. (2004) and Barklem et al. (2005) HERES Survey - Barklem et al. (2005) [Ba/Fe] 82% at [Fe/H] ≤ -2.5 show r-process enrichment

Figure from Aoki et al. (2006) Hyper-Metal-Poor Puzzles From Hamburg-ESO Survey: [Fe/H] = -5.3 and -5.6 Abundance patterns are highly non-solar and unlike other C-rich stars at [Fe/H] ~ -3. Are these abundances “primordial” or acquired later? Christlieb et al. (2004) Frebel et al. (2005)

Because the observed abundance patterns involve “nucleosynthesis” and “chemical evolution”, the full synthesis demands a set of coupled equations including: 1. “Source terms” – existence proofs for abundance patterns. 2. “Coupling” terms – construct global pattern by mixing sources within the mass accretion and star formation history, including mass function. These tracks are mutually interactive, informative and iterative, as we search for and solve the governing equations. Two-track Approach in the Field (and the talk)

Primordial Nucleosynthesis by Mass Range By Stellar Mass Adapted from Alex Heger – Mass Ranges of Interest 8 – 40 M סּ Core-collapse SNe Hypernovae? Faint Supernovae? 140 – 260 M סּ PISNe?

Specimens from the Supernova Zoo SN 1998bw E 51 ~ 50 M( 56 Ni) ~ 0.5 M סּ Hypernovae: Energetic “Type Ic” SNe and GRBs. See poster by Tominaga, papers by Nomoto et al. (2003), Umeda & Nomoto (2005) Faint SNe: Underluminous, slow Type IIs (Turrato et al. 1998, Zampieri et al. 2003) Can these unusual explosion explain the surprising abundances of EMPs? Compiled from: Zampieri et al Mazzali et al NameE 51 M( 56 Ni) 1987A bw dh D bw NameE 51 M( 56 Ni) 1987A bw dh380.3 NameE 51 M( 56 Ni) 1987A

Stars with M = 140 – 260 M סּ subject to pair instability. Complete disruption after core He burning (Fowler+Hoyle1964). Robust yields (Heger+Woosley 2003, Umeda+Nomoto 2005), with no rotation or mass loss. Unique nucleosynthetic patterns make the “VMS hypothesis” easy to test (Tumlinson, Venkatesan, & Shull 2004). The “VMS Hypothesis”

Larger zones of complete Si burning enhance Co, Zn and reduce Cr, Mn, matching observed reversal in trends better than E 51 = 1 (Umeda+Nomoto 2005). See also Yoon & Langer (2005) for mechanism. Are hypernova the dominant mode of explosion at Z = 0? Hypernovae and the “Typical EMP” VLT data - Cayrel et al. (2003) and Barklem et al. (2005)

VMS and Nucleosynthesis? Tumlinson, Venkatesan, & Shull (2004) Yields of individual VMS/PISN compared to Galactic Pop II stars: Widespread r elements rule out IMF of pure VMS (but... ) To match observed Fe-peak ratios and odd-even effect, VMS cannot contribute more than ~½ of Fe to early chemical evolution. Yields: Heger+Woosley - Data: McWilliam95, Carretta02, Cayrel04

“Faint SNe” and Hyper-Metal-Poor Stars? In “faint SNe”, most explosive products end up in BH. “Mixing and fallback” in ejecta and E 51 -M cut relation self- consistently explain HMP abundance patterns. [Na-Mg-Al/Fe] sensitive to M cut, should scatter at low [Fe/H]. By comparison, PISNe are poor fit to these abundances. Iwamoto et al. 2005, Science, 309, 451 Data from Christlieb; Frebel M cut

Or is it fast rotation at Z = 0? Rotation-driven mass loss threatens an otherwise clean picture. Angular momentum requires faster rotation at Z = 0? Rotational mixing and metal-rich mass loss responsible for high CNO? Another worry – rotation may allow VMSs to avoid PISNe! AGB mass loss? Winds + SNe? Winds? Plot= Iwamoto; Data = Christlieb; Frebel Meynet, Ekstrom, Maeder (2006) Chiappini et al. (2006)

HMP abundance patterns may also be produced by jet- induced explosion in 2D hydrodynamical models. Could be connected with high-z GRBs? See the poster by Tominaga et al. for details! Late-breaking possibility – A Jet-induced Explosion? E 51 = 0.05 – 0.15 in jet

How Do These All Fit Together? “Existence proofs” Qualitative trends in Fe-peak abundances => HNe Low [Fe/H] and high [C/Fe] in HMPs => faint SNe or rotation? Abundant r-process, Fe-peak, and CNO disfavor VMS/PISNe. Interesting Questions Q. How does a star know its own E 51 ? A. Nobody knows. Models explode by hand! Q. What is the distribution of E 51 and/or V rot ? A. Unknown, but may be able to constrain this with relative incidence of their distinctive abundance patterns. This leads us from nucleosynthesis to chemical evolution, and its most important ingredient - the IMF!

New Framework Needed to Address Rich Data The proper context of early chemical evolution is the small pre-Galactic dark matter halos of 10 6 – 10 7 M סּ at z > 10. We therefore need a theoretical framework that: 1) operates within the hierarchical theory of galaxy formation, and 2) tracks chemical evolution “one star at a time”.

A New Synthesis for Stochastic Chemical Evolution CDM halo merger trees - a natural approach to stochastic chemical evolution. Each node is a semi-closed box within which stellar birth, death, and ISM mixing evolve stochastically, keeping track of all massive stars. Best of all, these “boxes” can be modeled as individual galaxies for direct comparisons to data at high redshift. Tumlinson 2006, ApJ, 641, 1

Key Component: The Log-Normal IMF Well-suited to the wide range of mass and shapes possible in primordial gas, with only one more parameter. m c = characteristic mass  = Gaussian width of distribution  mcmc “VMS” “Top-heavy”  = -2.35

Key Result: The Metallicity Distribution Function (MDF) ChemTree model matches halo MDF (~300 stars from Ryan & Norris ‘91; >10000 to come from SDSS-SEGUE). No known Z=0 stars, so fraction F o = 1/N(<2.5) = Z crit F o ≤ 1/N(<2.5) ≤ Tumlinson 2006, ApJ, 641, 1

Joint Constraints on IMF from Halo MDF, Pop II Stars, and Reionization: Low-metallicity IMF is confined to the unshaded region, with = 10 – 42 M סּ. This IMF does not overproduce Pop III stars (F 0 ) or VMS, and it produces enough ionizing photons for reionization. May imply strong feedback on accreting material during star formation. Constraints on Primordial IMF Tumlinson 2006, ApJ, 641, 1

Massive Stars: New Knowledge and New Problems 1) Abundances favor a wide range of E 51 for collapsing massive stars.... or rotation and strong mass loss in late stages... What are the causes and distributions of E 51 and V circ ? Problem: Advance models to understand formation and evolution. 2) Available data favors IMF peaked at 10 – 40 M סּ for most of Z = 0 mass. Problem: How is this produced (vs. M J ) ? Do E 51 or V rot matter? 3) The data we see are a complex admixture of distinctive nucleosynthetic yields and gas physics, which we must unravel to test our theories. Problem: Create numerical methods to extract optimal information. Can we distinguish primordial stars by place of formation? We have much to learn about the first stars, and massive stars generally, from studying their unique residues at low metallicity. There is perhaps more information about the first stars at z = 0 than at z > 6.

Want to know more? Study those GKM stars! GOOD: Precise abundances for ~100 stars on VLT & Keck. BETTER: Sloan Extension for Galactic Understanding and Exploration (SEGUE) and Radial Velocity Experiment (RAVE) will discover > thick disk and halo stars at [Fe/H] < -2, for later highres followup. BEST: WFMOS: Wide Field Multi-Object Spectrograph ~ 1 million stars with automatic high-res followup GAIA (ESA) ~ 10 9 stars with kinematics and [Fe/H] for followup.. Next-generation large telescopes (GSMTs) can push these studies into nearby galaxies and probe the different chemical evolution histories of different types and masses.

Extra Slides Follow

-4 -3 [Fe/H] A Fundamental Disconnect average over mass and metallicity But we know that each Pop II star is an average over mass and metallicity, so we need to know M and [Fe/H] for all progenitors to properly apply yields. Also, despite diligent theoretical efforts, there is still no “basis set” of yields. We therefore need a quantitative model that maps intrinsic SNe yields to the data, in the proper astrophysical context of early chemical evolution. [Co/Fe] [Ni/Fe] [Zn/Fe] ? Tominaga et al.(2005) courtesy K. Nomoto

Hypernovae and GRBs? Mazzali et al. 2003, ApJ, 599, L95 SN 1998bw E 51 ~ 50 M( 56 Ni) ~ 0.5 M סּ SN 2003dh E 51 ~ 38 M( 56 Ni) ~ 0.3 M סּ Energetic SNe “Type Ic” linked to GRBs. “Mixing and fallback” needed to get proper abundances. See poster by Tominaga for detailed physics. Posit that these exist at Z = 0 and calculate nucleosynthesis. Nomoto et al. (2003), Umeda & Nomoto (2005) SN 1987A

Hypernovae and Nucleosynthesis A Possible Solution: Energetic “Hypernovae” in the First Generation: - Larger zones of complete Si burning enhance Co, Zn and reduce Cr, Mn, matching observed trends. (Umeda+Nomoto2005). - For calculated yields, hypernova fraction in first generation approaches f HN = 1 to match data on Co, Mn, Cr, Zn, and f HN > 0.5 at 90%+ confidence from discrete histories. Tumlinson, Venkatesan, & Shull (2004) Yields: Umeda+Nomoto04 - Data from McWilliam95, Carretta02, Cayrel04

One Slide on SN Ia/AGB from Metal-free Stars Are there any constraints on binary fraction? Prob must come from chem ev? Lucatello? Any more information on SN Ia at Z = 0? Where to start searching? see Siess et al for 1 – 8 Msun ev + nuc.

Specimens from the Supernova Zoo Low-luminosity SNe with seen locally. Optical spectra imply ~ 0.1 – 0.5 x erg and M( 56 Ni) ~ (Turrato et al. 1998, Zampieri et al. 2003) Zampieri et al Mazzali et al SN 1998bw E 51 ~ 50 M( 56 Ni) ~ 0.5 M סּ SN 2003dh E 51 ~ 38 M( 56 Ni) ~ 0.3 M סּ SN 1987A Energetic “Type Ic” SNe and GRBs. “Mixing and fallback” may also exist. See poster by Tominaga, papers by Nomoto et al. (2003), Umeda & Nomoto (2005) for details. Posit that these unusual objects exist at zero metallicity, and ask whether they can explain the observed abundances in metal-poor stars.

IMF Test Cases: Constrained by Pop II star counts, reionization, and chemical abundances. Sharp peak at 10 – 40 M The First Stars IMF?  = Tumlinson 2006, ApJ, 641, 1

Chemical Evolution Approaches the “Precision Era” Detailed Yields for Metal-Free Stars: - These are the yields that best map the stellar histories in the chemical evolution model to data on 35 stars from Cayrel et al. (2004). - These results offer the most direct comparison that the data will allow for comparing to ab initio SN models (i.e. Heger, Nomoto). - Detailed empirical yields will soon be available for a wide range of progenitor mass and metallicity, and will improve as data grows. Z = 0, IMF A Tominaga et al.(2005) courtesy K. Nomoto

Unraveling Chemical Evolution “One Star at a Time” For a given model, the model follows self-consistently the metallicity and mass distribution of progenitors that produced a Pop II star. Below [Fe/H] = -3, all supernova progenitors of Pop II stars are metal-free, so we can compare [Fe/H] < -3 yields directly with theory, and address IMF. Pure Z = 0 progenitors!

HERES Survey - Barklem et al. (2005) [Ba/Fe] [Fe/H] 82% at [Fe/H] ≤ -2.5 show r-process enrichment VLT data - Cayrel et al. (2003) and Barklem et al. (2005) Thousands of metal-poor stars from decades of surveys, more to come. Fe-peak elements: small scatter, reversal and separation at low [Fe/H] r-process: > 2 dex scatter, including some very r-enhanced (r-II) stars. Rich New Data, Puzzling New Patterns 1 01