constraining galactic infall with deuterium observations

Tijana Prodanović, University of Novi Tijana Prodanović, University of Novi SadSadBrian D. Fields, University of Illinois at Urbana Champaign

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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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!

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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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!

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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51031.2 dustISMHD

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

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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Increases ISM D abundance Increases gas content of the Galaxy Dilutes metal content of the Galaxy

Turns out:

Deuterium and Galactic gas Deuterium and Galactic gas fraction observations powerful fraction observations powerful

constraint of the infall rateconstraint of the infall rate

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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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

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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)(tM baryon )(t

)()()( tMtMt baryonISM

3.0R

D vs. gas fraction Shaded =

observations Solution must

satisfy both

Allowed infall rate

Almost balances out star-formation!

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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15.0

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

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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4.01.0 R

4.0R

Local ISM D severely depleted onto dust Local ISM D abundance could be close to

primordial Then … Local D and gas fraction observations demand demand

large infall rate , close to star-large infall rate , close to star-formation rateformation rate

Consistent with hierarchical assembly of Consistent with hierarchical assembly of galaxies by accretiongalaxies by accretion

Modern IMFs demand return fraction Modern IMFs demand return fraction R~0.4 R~0.4 , , but only marginally consistent with our but only marginally consistent with our resultsresults

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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15.0

Prodanovic & Fields, Journal of Cosmology and Astroparticle Physics, Issue 09, pp. 003(2008)

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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pISM

ISM

DDDMdt

d

Rdt

dM

)(

)1(

Where D is the deuterium mass fraction defined as: Hbaryon

DD X

H

DXD

2

Taking we get:)0()( tMtM baryonISM

R

R

p RR

R

D

tD

1)(

which we can express in terms of the present gas mass fraction by using:

)()(1

1)( t

tR

R

M

Mt

baryon

ISM

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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)()( mmmmm remej Approximate:

Then, define return fraction for each progenitor mass as: mmmR ej)(

To find a global return fraction must specify the IMF: dmdNm )(

U

L

U

L

m

m

m

m

mmdm

mmmRdm

R

)(

)()(

For mass ranges

and Salpeter IMF

we find return fraction

880. and 1008 solAGBsolSN MmMm

35.2)( mm

31.0R

Modern IMFs are flatter in the high-mass regime → more high-mass stars → more ejecta→ larger return fractions 4.0~R

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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R

R

p RR

R

D

tD

1)( )()(1

1)( t

tR

R

M

Mt

baryon

ISM

For large infall where 1R

rD

D

R

R

p

R

R

min

1 001

R

tt

Rt

tR

R

tR

11

)()(

1)(

)(1

1

)(1

min

For small infall where 1R

0

0 0

min

min1

RD

D

p

R

R

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

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Freshly synthesized metals syntZ

SN metal yield

Present reasonable estimates

solSN ZZ 10~

4ISMsynt ZZ

consistent with large or no infallsince all curves converge.

Tijana ProdanovićXV National Conference of Astronomers of Serbia, October 4th 2008

15Cyburt et al. (2004)