1 / 30

Lecture 10 Metalicity Evolution

Lecture 10 Metalicity Evolution. Simple models for Z ( m ( t ) ) ( Closed Box, Accreting Box, Leaky Box ) Z = - y ln( m ) = y ln( 1 / m ) “ G dwarf problem ” Closed Box model fails, predicts too many low- Z stars.

chidi
Download Presentation

Lecture 10 Metalicity Evolution

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 10 Metalicity Evolution • Simple models for Z( m( t ) ) • (Closed Box, Accreting Box, Leaky Box) • Z = - y ln( m ) = y ln( 1 / m ) • “G dwarf problem” Closed Box model fails, predicts too many low-Z stars. • No Pop III (Z=0) stars seen (were they all high mass?). • Infall of Z = 0material causes Z => y. • Observed Yields: • Yeff = Zobs / ln(1/m) ~ 0.01 • ~0.001 in small Galaxies • (SN ejecta escape)

  2. Lecture 11: Ages and Metalicities from ObservationsA Quick Review

  3. HR diagram . . . MV MV(TO) B-V Agesfrom main-sequence turn-off stars Main sequence lifetime: lifetime = fuel / burning rate Luminosity at the top of the main sequence (turn-off stars) gives the age t.

  4. Ages from main-sequence turn-off stars MV(TO) = 2.70 log ( t / Gyr ) + 0.30 [Fe/H] + 1.41 Globular Cluster in Halo Open Clusters in Disk M67: 4 Gyr NGC188: 6 Gyr 47 Tuc: 12.5 Gyr

  5. Multiple Ages of stars in Omega Cen

  6. Star Formation Rates

  7. Cosmic Star Formation History

  8. Star spectra: absorption lines Gas spectra: emission lines Galaxy spectra: both Metal-rich/poor stars: stronger/weaker metal lines relative to H. Abundance Measurements Stellar spectra HII region spectra

  9. Lab measurements: Unique signature (pattern of wavelengths and strengths of lines) for each element.

  10. High-Resolution Spectra Measure line strengths (equivalent widths) for individual elements. Equivalent Width measures the strength (not the width) of a line. EW is width of a 100% deep line with same area.

  11. Abundance Measurements Spectra Line strengths (equivalent widths) + Astrophysics Stellar atmosphere models + Physics Laboratory calibrations Abundances: (Temperature, surface gravity, and metal abundances in the stellar atmosphere models are adjusted until they fit the observed equivalent widths of lines in the observed spectrum. Full details of this are part of other courses)

  12. atoms of Fe atoms of H . . Bracket notation for Fe abundance of a star relative to the Sun: And similarly for other metals, e.g. relative to Fe: Star with solar Fe abundance: Twice solar abundance: Half solar abundance: Bracket Notation

  13. . . . . . . . . Metallicity vs Abundance Metalicity (by mass): Abundance (by number): To infer Z from a single line: Primordial: Xp = 0.75, Yp = 0.25, Zp = 0.00 Solar: X = 0.70, Y = 0.28, Z = 0.02

  14. Solar Abundances

  15. Solar Abundances

  16. Primordial He/H measurement Emission lines from H II regions in low-metalicity galaxies. Measure abundance ratios: He/H, O/H, N/H, … Stellar nucleosynthesis increases He along with metal abundances. Find Ypby extrapolating to zero metal abundance.

  17. [Xi/Fe] vs [Fe/H] Most metals enrich at approx same rate as Fe (e.g. to a factor of 2-3 over a factor of 30 enrichment). Some elements (Mg,O,Si,Ca,Ti,Al) formed early, reaching 2-3 x Fe abundance in metal-poor stars Lowest metal abundance seen in stars: [Fe/H] ~ -4 Na O Mg Al Si Y Ca Zr Ti Ba Ni Nd

  18. Enhancement of a- Elements a-elements = multiples of He, more stable, produced by Type II Supernovae (high-mass stars, M > 8M) Stars with high a elements must have formed early, e.g. before a less a-enhanced mix added to ISM by Type Ia SNe (WD collapse due to accretion from binary companion). Most MW bulge stars are a-enhanced => Bulge must have formed early. [O/Fe] [O/Fe] [Fe/H]

  19. Some Key Observational Results • Gas consumption: More gas used --> higher metallicity. • Radius: more metals near galaxy centre • Near centre of galaxy: Shorter orbit period--> More passes thru spiral shocks --> More star generations --> m lower --> Z higher. (Also, more infall of IGM on outskirts.) • Galaxy Mass : Low-mass galaxies have lower metallicity. • Dwarf irregulars: form late (young galaxies), have low Z because m is still high. • Dwarf ellipticals: SN ejecta expel gas from the galaxy, making m low without increasing Z.

  20. UV light traces hot young stars, current star formation. Gas depleted, hence no current star formation in the inner disk. M31: Andromeda in Ultraviolet Light

  21. More metals near Galaxy Centres Ellipticals (NGC 3115) Spirals (M100)

  22. Mass-Metalicity relation Why are low-mass galaxies are metal poor? Some are young (not much gas used yet, so ISM not yet enriched). Supernovae eject the enriched gas from small galaxies.

  23. faint ----> bright Less Metals in Small Galaxies

  24. SFR Stellar Mass • Two fundamental parameters seem to determine observed metallicity: • mass and SFR. • This forms a fundamental metallicity relation (FMR). • Despite extremely complex underlying physics, the relation seems to hold out to z = 2.5 and in a huge range of galaxies / environments. Stellar Mass

  25. More Metals => More Planets Doppler wobble surveys find Jupiters orbiting 5% of stars with solar metalicity. This rises to 25% for stars with 3x solar abundance [Fe/H]=+0.5 Fischer & Valenti 2005

  26. A Quick Review • Main events in the evolution of the Universe: • The Big Bang (inflation of a bubble of false vacuum) • Symmetry breaking  matter/anti-matter ratio • Quark + antiquark annihilation  photon/baryon ratio • The quark soup  heavy quark decay • Quark-Hadron phase transition and neutron decay  n/p ratio • Big Bang nucleosynthesis  primordial abundances Xp = 0.75 Yp = 0.25 Zp = 0.0 • Matter-Radiation equality R ~ t1/2  R ~ t2/3 • Recombination/decoupling  the Cosmic Microwave Background • CMB ripples (T/T~10-5 at z=1100) seed galaxy formation • Galaxy formation and chemical evolution of galaxies

  27. Main events in the chemical evolution of galaxies: • Galaxy formation  Jeans Mass ( ~106M ) • Ellipticals Initial mass and angular momentum, plus mergers. • Spirals  Star formation history S( t ), gas fraction m( t ) • Irregulars • Star formation  a = efficiency of star formation • The IMF ( e.g., Salpeter IMF power-law with slope -7/3 ) • First stars (Population III) from gas with no metals (none seen) • Stellar nucleosynthesis  metals up to Fe • Supernovae (e.g. SN 1987A)  metals beyond Fe • p, s, and r processes • white dwarfs (M < 8 M) or black holes, neutron stars (M > 8 M). • Galaxy enrichment models: (e.g. Z = - y ln(m yield y) • Metal abundances rise  X = 0.70 Y = 0.28 Z = 0.02 (solar abundances) • Gas with metals  Stars with Planets  Life!

  28. fini

  29. Metalicity Gas fraction Yield Lecture 11: Age and Metalicity from Observations • “Closed Box” model with constant Yield: • Closed Box model ignores: • IGM--ISM exchanges: IGM falls in, ISM blown out of galaxy • 2. SN Ia, stellar winds, PNe, novae, etc. • Initial enrichment by e.g. Pop.III stars prior to galaxy formation? • Faster enrichment (more SNe) in denser regions of galaxy. But (with infall):

More Related