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First Light from the Fossil Record: A New Synthesis

(1) A Review of Major Themes in the Study of “First Stars” (2) A New Approach to Constraints on the IMF of Primordial (“First”) Stars (3) The IMF of the “Second” Stars (4) Predictions and Future Tests. First Light from the Fossil Record: A New Synthesis. Jason Tumlinson

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First Light from the Fossil Record: A New Synthesis

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  1. (1) A Review of Major Themes in the Study of “First Stars” (2) A New Approach to Constraints on the IMF of Primordial (“First”) Stars (3) The IMF of the “Second” Stars (4) Predictions and Future Tests First Light from the Fossil Record: A New Synthesis Jason Tumlinson Yale Center for Astronomy and Astrophysics A slice of the Milky Way at z = 6

  2. The Big ??: When, What, and Where was “First Light”? Quick Answer: A Major Frontier of 21st Century Astrophysics

  3. Major Themes of “The First Stars” Physical Models of Star Formation at Zero and Very Low Metallicity Stellar Evolution and Nucleosynthesis of the First Stars Chemical Abundance Studies of Metal-Poor Pop II (“Galactic Archaeology”)

  4. Simple recipe for first stars: LCDM Dark matter “minihalos” of MDM ~ 106-7 M€ at z = 20 - 40. primordial composition (H,He,H2) the absence of other (in)famously complicating factors (dust, B) Key Concept #2: “The Critical Metallicity” and the “2nd Stars” At Zcrit ~ 10-5.5 to 10-3.5Zסּ, efficient metal-line cooling may allow fragmentation to low-mass stars (Bromm & Loeb 2003; Santoro & Shull 2006). But by this time there may also be dust, ionizing radiation, the CMB, cosmic rays, B fields. . so ab initio simulation is too hard. To cut the knot of theory, we need observations! Key Concept #1: “Warmer (Primordial) Gas Forms Heavier Stars” H2 cools primordial gas to Tmin ~ 200 K, for MJ ~ 100 - 1000 Mסּ (Bromm, Coppi, & Larson 1999; 2002, Abel, Bryan, & Norman 2002) 30 – 300 Mסּ accretes in a Kelvin-Helmholz time (O’Shea & Norman 2007). Red = Bound at z = 10

  5. Major Themes of “The First Stars” Physical Models of Star Formation at Zero and Very Low Metallicity: Approach: Hydrosims of gas physics in early cosmological halos Key Results: High mass range (~30 - 300) for limiting Z = 0 case. Formation of first low-mass stars depends on prior ionization and/or metal enrichment metals, dust, CMB, other factors (?) How did the first and second stars form, and what was their IMF? Stellar Evolution and Nucleosynthesis of the First Stars: Approach: numerical stellar evolution and supernova models (1-D) Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”)

  6. Number per Mass Bin M Key Idea: The chemical signatures of stars vary with initial mass and metallicity in complex but calculable fashion. Our strategy is to use robust and distinct signatures of stellar mass to diagnose IMF.

  7. Major Themes of “The First Stars” Physical Models of Star Formation at Zero and Very Low Metallicity: Approach: Hydrosims of gas physics in early cosmological halos Key Results: High mass range (~30 - 300) for limiting Z = 0 case. Formation of first low-mass stars depends on prior ionization and/or metal enrichment metals, dust, CMB, other factors (?) How did the first and second stars form, and what was their IMF? Stellar Evolution and Nucleosynthesis of the First Stars: Approach: numerical stellar evolution and supernova models (1-D) Key Results: “Pair Instability SNe” and “Hypernovae” may arise from the first stars and give distinctive yield patterns. Big question now is how much rotation alters mass loss and yields. Given a particular IMF, what are the observational signatures (both radiation and chemical yields)? Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”):

  8. The Future of “Galactic Archaeology” 10000 from RAVE (AAO – now) >100000 from SDSS/SEGUE for halo, APOGEE for bulge and disk 109 from GAIA (ESA-2011) 100000 from LAMOST (China - 2009) Massive spectroscopic multiplexing enables surveys of > 106 stars for studies of MW structure and formation. Up to >~ 105 of these stars will have [Fe/H] < -2, so are plausibly from the first few generations. About 1% of the abundance data that will exist in 2013 is in hand and analyzed today. But what information about the first galaxies might these stars provide? Dwarf Abundance and Radial Velocities (DART) @ VLT 106 from WFMOS @ Subaru (2010?)

  9. “Information Overload” from Chemodynamical Probes of Galactic Evolution “Primary” Beers & Christlieb (2005) ARA&A “Hydrostatic” “Explosive” HERES Survey - Barklem et al. (2005) – 15 elements in 253 stars [X/Fe] “neutron capture” [Fe/H] Measured proper motion, radial velocity, and position trace galactic components – disk, bulge, or halo. Color, luminosity, Teff, and metallicity select old, low-mass stars with [Fe/H] < -2 that most likely trace the first generations. Expand this ~30-D “data space” by at least four orders of magnitude and you begin to get the idea.

  10. VLT data - Cayrel et al. (2004) and Barklem et al. (2005) ≥ 82% at [Fe/H] ≤ -2.5 show r-process enrichment [Ba/Fe] HERES Survey - Barklem et al. (2005)

  11. Carbon-Enhanced Metal-Poor Stars (CEMPs): after Komiya et al. (2007) CEMP = [C/Fe] > 1 @ [Fe/H] < -2 Beers & Christlieb (2005) HE1327-2326 HE0107-5240 “HMPs” “C-normal “ ~ solar 100% 100%

  12. Major Themes of “The First Stars” Physical Models of Star Formation at Zero and Very Low Metallicity: Approach: Hydrosims of gas physics in early cosmological halos Key Results: High mass range (~30 - 300) for limiting Z = 0 case. Formation of first low-mass stars depends on prior ionization and/or metal enrichment metals, dust, CMB, other factors (?) How did the first and second stars form, and what was their IMF? Stellar Evolution and Nucleosynthesis of the First Stars: Approach: numerical stellar evolution and supernova models (1-D) Key Results: “Pair Instability SNe” and “Hypernovae” may arise from the first stars and give distinctive yield patterns. Big question now is how much rotation alters mass loss and yields. Given a particular IMF, what are the observational signatures (both radiation and chemical yields)? Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”): Approach: massive surveys to discover stars at [Fe/H] < -2, followed by high-res spectra to obtain abundance patterns. Key results: discovery of HMPs with [Fe/H] <~ -5 and widespread strong enhancement of Carbon, the CEMPs. Where are the oldest low-mass stars, and what do they tell us about star and galaxy formation during the Epoch of First Light?

  13. (1) A Quick Review of Major Themes in the Study of “First Stars” So, how can we use Galactic Archaeology to study the first stars? First Major Conclusion: The theory of “First Light” is developed to the point of having some testable predictions, which can be addressed in the near term with rapidly growing data from “Galactic Archaeology” and in the long term with JWST.

  14. The Challenge to Theory As the sample sizes and dimensionality of the data explode, the theoretical challenge is to: • make sense of all this data • come to grips with the awesome statistics • define what “information” is present • place the observations in the proper context of high redshift • properly translate physical theory into the data space. . . . In short, to create a “Virtual Galaxy” that will synthesize all this data, in the high redshift context. Star Formation Theory Nucleosynthesis Structure Formation Observations! + + =

  15. A New Synthesis of Chemical Evolution & Structure Formation 25 20 15 z 10 5 0 HIERARCHICAL: Halo merger trees allow for chemical evolution calculations much faster than full hydro simulations, much more realistic than “classical” GCE. STOCHASTIC: Within each node, gas budget is tracked and new star formation samples the IMF “one-star-at-a-time”. New star formation is assigned a metallicity based on random sampling of “enrichment zones” from prior generations. UNIFIED: Best of all, these “nodes” can be modeled as individual galaxies for direct comparisons to data at high redshift – this is also the core of a galaxy formation code. Pop III Halos “Milky Way” Tumlinson 2006, ApJ 641, 1

  16. “Salpeter” Z ≥ Zcr a = -2.35 “Log-normal” Z < Zcr Number per Mass Bin mc “Very Massive Stars” s

  17. Discrete, Stochastic Chemical Evolution, “One Star at a Time” Tumlinson 2006 Zcrit = 10-4 Fo≤ 1/N(<2.5) ≤ 0.0019 Pure Z = 0 progenitors! “Pop II” [Fe/H] “Pop II” [Fe/H]

  18. Tumlinson, Venkatesan, & Shull (2004) Yields: Heger+Woosley - Data: McWilliam95, Carretta02, Cayrel04 PISNe yields are characterized by big “Odd Even Effect” and no neutron capture nucleosynthesis. Observed Fe-peak, eg. [Zn/Fe], require ≤ ½ of Fe from PISNe. PISNe have no r-process, so cannot give 82% of EMPs with Ba.

  19. Constraints on the Primordial IMF Too many “True” Pop III stars. Tumlinson (2006) Too much Fe from PISNe A C Too little r-process B

  20. Convergence on the First Stars IMF? “Data” “Theory” Tumlinson 2006a, ApJ, 641, 1 a = -2.35 B Number per Mass Bin C A Theory is still missing feedback of young star on final mass?

  21. (2) A New Approach to Constraints on the IMF of Primordial (“First”) Stars Q: How can we study the IMF at Z > 0, i.e. for most stars during the Epoch of “First Light”? Second Major Conclusion: Using a new synthesis of theory that tracks stochastic early chemical evolution in the proper high-z, hierarchical context, we can show that the first stars were predominantly massive stars, but find hints that additional feedback might be needed in simulations to resolve remaining discrepancy.

  22. A: The CEMPs! CEMP = [C/Fe] > 1 @ [Fe/H] < -2 Beers & Christlieb (2005) HE1327-2326 HE0107-5240 after Komiya et al. (2007) 100% 40% 20% 10% The Answer: CEMP stars are born as low-mass partner in a binary system. 80% are CEMP-s that are rich in s-process elements (indicating AGB). CEMP-s consistent with 100% binarity (Lucatello et al. ’05).

  23. From CEMPs to the IMF Primary 1.5 - 8 Mסּ LMS CEMP M ~ 0.8 Mסּ IMS 0.5 1.5 8 40 IMS LMS 0.5 1.5 8 40 0.8 + IMS binaries are favored. High fCEMP. 0.8 + 0.8 binaries are favored. “Low fCEMP” The ratio of C-rich to C-normal stars in a population measures the ratio of intermediate to low-mass stars in the IMF! Estimate from early CEMP studies: Mc > 0.8 Mסּ (Lucatello+05). There are no C-normal stars at [Fe/H] = -5.5, so Mc = 1.5 - 6 Mסּ(Tumlinson07). Komiya+2007 find mc ~ 10 Mסּ to match s-element patterns of CEMPs.

  24. Zcrit Tumlinson (2007a) C-rich Pop II stars “CEMP” MW Why would the IMF form more IMS, if Z ~ 10-3Zסּ is high enough to cool efficiently (Bromm+Loeb03, Schneider+02)?

  25. Two Key Concepts: Importance of Cooling Physics Key Concept #1: “Warmer (Primordial) Gas Forms Heavier Stars” H2 cools primordial gas to Tmin ~ 200 K, for MJ ~ 100 - 1000 Mסּ (Bromm, Coppi, & Larson 1999; 2002, Abel, Bryan, & Norman 2002) 30 – 300 Mסּ accretes in a Kelvin-Helmholz time (O’Shea & Norman 2007). Studies of local star formation (Larson ‘98,’05; Jappsen et al. ’05) suggest that the characteristic mass of stars responds to the minimum T at which gas becomes optically thick to cooling radiation and thermally coupled to dust. At low redshift, Z = Zmin = 10 K is set by metal and dust cooling. But at high z, the CMB at T = 2.73(1+z) K sets the minimum gas temperature! Thus stars formed early in MW history, at z > 5, should be affected! MC≈ 0.9 Mסּ [TCMB/10K]1.70-3.35 z = 5, 10, 20 TCMB = 16, 30, 57 K MC = 2, 6, 17 Mסּ

  26. (3) CEMPs and the IMF of the “Second” Stars Q: How can we test the CMB-IMF hypothesis?A: Look for agreement between what we see as old in the nearby Universe and what we see as young in the distant Universe. Third Major Conclusion: IMF diagnostics in the most metal-poor stars, interpreted by a new hierarchical, stochastic theoretical framework, show evidence for a top-heavy IMF at high redshift that may be physically independent of metallicity.

  27. Low-z Test #1: Variation of CEMP Fraction with Metallicity With a CMB-IMF, fCEMP is high at low [Fe/H], and declines with increasing [Fe/H] as the typical formation redshift at a given metallicity declines. (Tumlinson 2007b, ApJL, 664, L63) Stochastic, local phenomenon of chemical evolution implies that, on average, more metal-poor stars form earlier, so fCEMP should increase with declining [Fe/H]. Tumlinson (2006) stochastic MW HMPs

  28. Key Idea for Prediction 2: The Halo is Built from the Inside Out. . . Inside-out construction the halo causes extended epoch of star formation at fixed [Fe/H], so fCEMP should increase in “older” regions of the Galaxy and decrease in “younger” regions, at fixed metallicity.

  29. Also: Faint end of WD luminosity function? (JWST) fCEMP in dwarf spheroidals (GSMT)? Low-z Prediction #2: Variation of CEMPs with Galactic Location NCEMP NCEMP+NC-normal UPDATE The CMB-dominated mass scale at ~ 10 kpc is 2 -10 Mסּ. At a given metallicity, stars in the inner halo are older, and this gradient gives a gradient of C-rich/C-normal fraction.

  30. >100000 from SDSS/SEGUE for halo, APOGEE for bulge and disk SDSS-III = SEGUE-II (2008) + APOGEE (2011) SEGUE2: 105 more halo and thick disk stars w/ current SDSS spectrograph. APOGEE: H-band spectroscopic survey of 105 giants in inner disk and bulge. with the ARCHES spectrograph (PI Majewski at UVa). “Virtual Galaxy” will be important to comparing the results of the two surveys for chemical and kinematic substructure in the ancient MW.

  31. High-z Test: Mass-to-light ratios in High-z Galaxies van Dokkum (2008) technique from Tinsley (1980) When estimates of dynamical mass / light ratios of “first-light” galaxies become possible with JWST and GSMTs, expect to see M/L decline with redshift, 2 - 5 times lower than for a normal IMF.

  32. Because many of the first galaxies are still with us, “Galactic Archaeology” with growing stellar surveys can uncover unique insights into the history of star and galaxy formation during First Light. With this rich dataset and a new synthesis of theory, we can directly address some of the most pressing questions about the galaxies of “First Light” – such as how metallicity, redshift, and environment interact in shaping the IMF. Early indications are that the Pop III and early Pop II IMFs during the epoch of reionization preferred intermediate and massive stars, with major implications for observable features of galaxies by JWST. A new synthesis of theory is being developed to take advantage of this wealth of data, and connect it explicitly to high-z, as a perfect partner and complement to JWST. In the JWST era, we can test and extend these models to uncover a deep, unified view of First Light. The Morals of the Story

  33. A Three-fold Vision for the Future Theoretical: Complete the N-body theoretical framework, including many MW realizations, sharpened predictions for tests of the CMB-IMF hypothesis, and a systematic study of dSph abundances. Begin building framework for high-z. Observational: Collaborate (join?) with observers to test predictions and develop new ideas. Sloan SEGUE (current) > 20000 @ [Fe/H] < -2 Radial Velocity Experiment (RAVE, current), 10000+ SDSS3 = SEGUE2 (Halo) + APOGEE (Bulge) 2008 – probably most critical WFMOS: Wide Field Multi-Object Spectrograph (?) and others later The challenge: to integrate the results and make optimal use of all information. Unification: The goal is a full realization (gas included) that follows both a high-resolution MW to z=0 and a cosmological volume at high redshift. This model will allow us to test the same galaxy formation physics with both JWST and Galactic Archaeology data.

  34. Extra slides follow

  35. Two Key Concepts: Importance of Cooling Physics Key Concept #1: “Warmer (Primordial) Gas Forms Heavier Stars” H2 cools primordial gas to Tmin ~ 200 K, for MJ ~ 100 - 1000 Mסּ (Bromm, Coppi, & Larson 1999; 2002, Abel, Bryan, & Norman 2002) 30 – 300 Mסּ accretes in a Kelvin-Helmholz time (O’Shea & Norman 2007). ORIGINAL Key Concept #2: “The Critical Metallicity” and the “2nd Stars” At Zcrit ~ 10-5.5 to 10-3.5Zסּ, efficient metal-line cooling may allow fragmentation to low-mass stars (Bromm & Loeb 2003; Santoro & Shull 2006). But by this time there may also be dust, ionizing radiation, the CMB, cosmic rays, B fields. . so ab initio simulation is too hard. To cut the knot of theory, we need observations!

  36. Paths to Star Formation during “First Light” To understand the stars in “First Light” galaxies, we can apply some canonical diagnostic tests in the high-redshift Universe: - blue colors and unusual emission lines (He II) with JWST and 30-m - color and luminosity evolution in evolved populations - GP effect and other tracers of reionization (CMB, 21 cm, LAEs) However. . . . . . these tests require facilities that are some years away (2013+), and . . . they detect direct/reprocessed emission of massive stars, so  are insensitive to the bulk of the stellar mass (in a normal IMF), and  provide poor tests of star formation physics at very low metallicity. Both of these problems can be avoided if we look instead in the low-redshift Universe!

  37. Simple recipe for first stars: LCDM Dark matter “minihalos” of MDM ~ 106-7 M€ at z = 20 - 40. primordial composition (H,He,H2) the absence of other (in)famously complicating factors (dust, B) First Stars: The Hows and Whys Key Concept #2: “The Critical Metallicity” and the “2nd Stars” At Zcrit ~ 10-5.5 to 10-3.5Zסּ, efficient metal-line cooling may allow fragmentation to low-mass stars (Bromm & Loeb 2003; Santoro & Shull 2006). But by this time there may also be dust, ionizing radiation, the CMB, cosmic rays, B fields. . so ab initio simulation is too hard. To cut the knot of theory, we need observations! Key Concept #1: “Warmer (Primordial) Gas Forms Heavier Stars” H2 cools primordial gas to Tmin ~ 200 K, for MJ ~ 100 - 1000 Mסּ (Bromm, Coppi, & Larson 1999; 2002, Abel, Bryan, & Norman 2002) 30 – 300 Mסּ accretes in a Kelvin-Helmholz time (O’Shea & Norman 2007). ORIGINAL Red = Bound at z = 10

  38. Major Themes of “The First Stars” Physics of Star Formation at Zero and Very Low Metallicity: Approach: Hydrosims of gas physics in early cosmological halos Key Results: High mass range (~30 - 300) for limiting Z = 0 case. Formation of first low-mass stars depends on prior ionization and/or metal enrichment metals, dust, CMB, other factors (?) How did the first and second stars form, and what was their IMF? Stellar Evolution and Nucleosynthesis of the First Stars: Approach: numerical stellar evolution and supernova models (1-D) Key Results: “Pair Instability SNe” and “Hypernovae” may arise from the first stars and give distinctive yield patterns. Big question now is how much rotation alters mass loss and yields. Given a particular IMF, what are the observational signatures (both radiation and chemical yields)? ORIGINAL Chemical Abundance Studies of Metal-Poor Pop II (“The Second Stars”): Approach: massive surveys to discover stars at [Fe/H] < -2, followed by high-res spectra to obtain abundance patterns. Key results: discovery of HMPs with [Fe/H] <~ -5 and widespread strong enhancement of Carbon, the CEMPs. Where are the oldest low-mass stars, and what do they tell us about star and galaxy formation during the Epoch of First Light?

  39. “Low-z” Predictions of the CMB-IMF Hypothesis (Tumlinson 2007a, ApJL, 664, 63) (1) Stochastic, local phenomenon of chemical evolution implies that, on average, more metal-poor stars form earlier, so fCEMP should increase with declining [Fe/H]. (2) Inside-out construction the halo causes extended epoch of star formation at fixed [Fe/H], so fCEMP should increase in “older” regions of the Galaxy and decrease in “younger” regions, at fixed metallicity. ORIGINAL

  40. Discrete, Stochastic Chemical Evolution, “One Star at a Time” Tumlinson 2006 Zcrit = 10-4 Fo≤ 1/N(<2.5) ≤ 0.0019 ORIGINAL Pure Z = 0 progenitors! “Pop II” [Fe/H] “Pop II” [Fe/H]

  41. IMF Theme 1: Theory of Star Formation in Early Universe Metal enrichment Reionization Kinetic Feedback Compact Objects Spectral Features Colors

  42. IMF Theme 1: Theory of Star Formation in Early Universe Cooling (Metals) Heating (adiabatic,CMB) Structure Formation Magnetic Fields Feedback Turbulence

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