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CONSTRAINING GALACTIC INFALL WITH DEUTERIUM OBSERVATIONS

Tijana Prodanović, University of Novi Sad Brian D. Fields, University of Illinois at Urbana Champaign. CONSTRAINING GALACTIC INFALL WITH DEUTERIUM OBSERVATIONS. Only created in Big Bang (Epstein et al. 1976, Prodanovi ć & Fields 2003 ) All other processes destroy it

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CONSTRAINING GALACTIC INFALL WITH DEUTERIUM OBSERVATIONS

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  1. XV National Conference of Astronomers of Serbia, October 4th 2008 Tijana Prodanović, University of Novi Sad Brian D. Fields, University of Illinois at Urbana Champaign CONSTRAINING GALACTIC INFALL WITH DEUTERIUM OBSERVATIONS

  2. Only created in Big Bang (Epstein et al. 1976, Prodanović & Fields 2003) • All other processes destroy it • Monotonic decline from high to low z • Deuterium – a powerful tool in cosmology! • Cosmic baryometer! BBN success story • Measure of how much gas was processed in stars! XV National Conference of Astronomers of Serbia, October 4th 2008 REALLY A STORY ABOUt DEUTERIUM...

  3. Large (factor of 3!) variations of D abundance in local ISM over different lines of sight! • Both high and low D abundances found • “Resolution” to the problem? (Linsky at al. 2006) • Deuterium severely depleted onto dust! • Measure lower bound on the “true” D • “True” ISM D abundance • “True” ISM D = 85% of PRIMORDIAL!? • Almost NO GASS was PROCESSED in stars!? recall: stars completely destroy D! XV National Conference of Astronomers of Serbia, October 4th 2008 BUT NOT SO SIMPLE …

  4. Deuterium must be replenished somehow • INFALL/ACCRETION OF PRISTINE GAS! • Eg. High-velocity clouds • falling on our Galaxy • some with metallicity ~10% Solar • little or no dust XV National Conference of Astronomers of Serbia, October 4th 2008 OR A DEUTERIUM FACELIFT …

  5. Increases ISM D abundance • Increases gas content of the Galaxy • Dilutes metal content of the Galaxy • Turns out: Deuterium and Galactic gas fraction observations powerful constraint of the infall rate XV National Conference of Astronomers of Serbia, October 4th 2008 PRIMORDIAL INFALL Changes things …

  6. Build a “keep it simple” model • Infall and NO outflow • Infall rate proportional to star-formation rate • Define gas mass fraction • Specify return fraction R – fraction of initiall stellar mass that is returned to ISM (follows from Initiall mass function); eg. from Salpeter IMF XV National Conference of Astronomers of Serbia, October 4th 2008 How much infall deuterium needs?

  7. D vs. gas fraction • Shaded = observations • Solution must satisfy both • Allowed infall rate • Almost balances out star-formation! XV National Conference of Astronomers of Serbia, October 4th 2008 Results: Infall rate constraint

  8. At late times D and gas fraction approach minimum values • Limiting curves above which no solutions for range of return fractions • Allowed only • Modern IMFs demand XV National Conference of Astronomers of Serbia, October 4th 2008 results: ImfconstRaint

  9. Local ISM D severely depleted onto dust • Local ISM D abundance could be close to primordial • Then … • Local D and gas fraction observations demand large infall rate , close to star-formation rate • Consistent with hierarchical assembly of galaxies by accretion • Modern IMFs demand return fraction R~0.4 , but only marginally consistent with our results XV National Conference of Astronomers of Serbia, October 4th 2008 CONCLUSIONS Prodanovic & Fields, Journal of Cosmology and Astroparticle Physics, Issue 09, pp. 003(2008)

  10. XV National Conference of Astronomers of Serbia, October 4th 2008 Thank You!

  11. XV National Conference of Astronomers of Serbia, October 4th 2008 Model: details Where D is the deuterium mass fraction defined as: Taking we get: which we can express in terms of the present gas mass fraction by using:

  12. XV National Conference of Astronomers of Serbia, October 4th 2008 model: details – Return fraction Approximate: Then, define return fraction for each progenitor mass as: To find a global return fraction must specify the IMF: For mass ranges and Salpeter IMF we find return fraction Modern IMFs are flatter in the high-mass regime → more high-mass stars → more ejecta → larger return fractions

  13. XV National Conference of Astronomers of Serbia, October 4th 2008 model: details - envelope For large infall where For small infall where

  14. XV National Conference of Astronomers of Serbia, October 4th 2008 D vs. Metal yields Freshly synthesized metals SN metal yield Present reasonable estimates consistent with large or no infall since all curves converge.

  15. XV National Conference of Astronomers of Serbia, October 4th 2008 bbn Abundances: SchraMM PLOT Cyburt et al. (2004)

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