constraining galactic infall with deuterium observations
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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)