Tijana prodanovi university of novi sad brian d fields university of illinois at urbana champaign
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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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Tijana prodanovi university of novi sad brian d fields university of illinois at urbana champaign

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


Really a story about deuterium

  • 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...


But not so simple

  • 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 …


Or a deuterium facelift

  • 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 …


Primordial infall changes things

  • 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 …


How much infall deuterium needs

  • 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?


Results infall rate constraint

  • 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


Results imf constraint

  • 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


C onclusions

  • 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)


Thank you

XV National Conference of Astronomers of Serbia, October 4th 2008

Thank You!


Model details

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:


Model details return fraction

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


Model details envelope

XV National Conference of Astronomers of Serbia, October 4th 2008

model: details - envelope

For large infall where

For small infall where


D vs metal yields

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.


Bbn abundances schramm plot

XV National Conference of Astronomers of Serbia, October 4th 2008

bbn Abundances: SchraMM PLOT

Cyburt et al. (2004)


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