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The (Un)True Deuterium Abundance in the Galactic Disk

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Presentation on theme: "The (Un)True Deuterium Abundance in the Galactic Disk"— Presentation transcript:

1 The (Un)True Deuterium Abundance in the Galactic Disk
kflajsflj IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović ? Tijana Prodanović, University of Novi Sad Gary Steigman, Ohio State University Brian D. Fields, University of Illinois at Urbana Champaign This is a false-color image of the star AE Aurigae (bright source of light slightly off center of image) embedded in a region of space containing smoke-like filaments of carbon-rich dust grains, a common phenomenon. Such dust might be hiding deuterium, an isotope of hydrogen, and stymieing astronomers' efforts to study star and galaxy formation. The FUSE satellite has surveyed the local deuterium concentration in the galaxy and found far more than expected. Because deuterium is a tracer of star and galaxy evolution, this discovery could radically alter theories about how stars and galaxy form. The (Un)True Deuterium Abundance in the Galactic Disk

2 kflajsflj IAU Symposium 268: Light Elements in the Universe, November 9th 2009 Tijana Prodanović STORY ABOUt DEUTERIUM Only created in Big Bang (Boesgaard & Steigman 1985) All other processes destroy it (Epstein et al. 1976, Prodanović & Fields 2003) Should (?) decrease monotonically from high to low z Deuterium – a powerful tool in cosmology! Cosmic baryometer! BBN success story WMAP & BBN (blue) and high-z obs. (yellow) – a match! Deuterium – a powerful tool in chemical evolution! Probes virgin ISM fraction! Schramm plot – yellow – WMAP, blue – D BBN 1 sigma curve Likelihood plot – blue – WMAP BBN primordial D, yellow – highredshift observations Cyburt et al. (2008)

3 kflajsflj IAU Symposium 268: Light Elements in the Universe, November 9th 2009 Tijana Prodanović The TroublE Large variations of D in local ISM over different lines of sight! Data from Linsky at al. (2006) Reasonable stellar processing: ISM D = 55% of primordial

4 kflajsflj IAU Symposium 268: Light Elements in the Universe, November 9th 2009 Tijana Prodanović SOLUTION? Deuterium preferentially (compared to H) depleted onto dust! (Jura 1982, Draine 2004, 2006) Measure lower bound on the “true” D “True” ISM D abundance (Linsky at al. 2006) “True” ISM D = 82% of PRIMORDIAL!

5 Galactic chemical evolutuon
IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović Galactic chemical evolutuon Deuterium destroyed through stellar cycling Astration factor (Steigman et al. 2007) But new FUSE high ISM D Most gas still unprocessed? Gas observations say ~20% of present baryonic mass in ISM But D observations say ~80% initial gas unprocessed! Thus GCE says INFALL NEEDED

6 How much infall? Assume infall rate ~ star form. rate
kflajsflj IAU Symposium 268: Light Elements in the Universe, November 9th 2009 Tijana Prodanović How much infall? Assume infall rate ~ star form. rate D vs. gas fraction Shaded = observations Allowed infall rate Almost balances out star-formation! Still tension with GCE Is ISM D really so high? Prodanovic & Fields 2008 Linsky et al. 2006 For R=0.3, but recent IMFs require R~0.4 D = deuterium mass fraction = rho_d/rho_baryon Thus is high D, then need high infall, but that puts more gas in the ISM and so stellar return fraction must be lower i.e. must have IMF which puts more stars at the low-mass end.

7 Prodanovic, Steigman & Fields (2009)
kflajsflj IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović A BAYESIAN approach Try something different – make (almost) no assumptions Bayesian analysis (introduced by Hogan et al. 1997) Use all available LOS Assume only a possible (dust) depletion Find 2-parameter maximum likelihood - Max. D abundance consistent with observations; a lower limit to true ISM D - Depletion parameter Neglect possible unmixed infall Prodanovic, Steigman & Fields (2009) arXiv:

8 Choice: Depletion distributions
kflajsflj IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović Choice: Depletion distributions Know nothing about (dust) depletion distribution Make as little assumptions Top hat – all levels of depletion equally probable Negative bias – favors large depletion Positive bias – favors low depletion Probability of finding the true, dust depleted ISM D given the max. gas phase D and depletion

9 Prodanovic, Steigman & Fields (2009)
kflajsflj IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović LB vs. Non-LB Local Bubble very different from non-Local Bubble LB – blue Uniform nLB – red Large scatter First treat separately Prodanovic, Steigman & Fields (2009) arXiv: 1 red on the left – 31 Com: more distant than all LB stars with low column and thus was included in LB in Linskys paper, but according to Pishkunov 1997, and Dring 1997, 31 Com has velocity inconsistent with LB and probably lies in hot ionized bubble toward galactic pole.

10 Results: Likelihood contours
kflajsflj IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović Results: Likelihood contours Prodanovic, Steigman & Fields (2009) arXiv: Top-hat depletion distribution 21 Local Bubble LOS 25 non-Local Bubble LOS All 46 LOS LB consistent with no depletion on all 3 depletion distributions Non-LB Marginally consistent with GCE

11 Results: true ism d abundance
IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović Results: true ism d abundance Use all 46 LOS Top-hat depletion distribution – highest max likelihood value Marginally consistent with Releases tension with GCE models Linsky et al. (2006)

12 Prodanovic, Steigman & Fields (2009)
kflajsflj IAU Symposium 268: Light Elements in the Universe, November 9th 2009 Tijana Prodanović Summary & conclusions If Local ISM D abundance close to primordial – problems with most GCE models Bayesian analysis following Hogan et al. (1997) Assume all variations due to (dust) depletion Analyze all LOS Tested 3 simple depletion distributions Top-hat gives max likelihood value “True” ISM D abundance new estimate: Prodanovic, Steigman & Fields (2009) arXiv:

13 problems Uniform LB D abundance vs. large scatter in nLB?
kflajsflj IAU Symposium 268: Light Elements in the Universe November 9th 2009 Tijana Prodanović problems Uniform LB D abundance vs. large scatter in nLB? LB - no depletion? nLB – large depletion? Is LB uniformily depleted? Is nLB enriched with unmixed infall? How do we discriminate? Is Fe really a good depletion indicator for D? Steigman & Prodanović (2009/10) in preparation

14 kflajsflj IAU Symposium 268: Light Elements in the Universe, November 9th 2009 Tijana Prodanović Thank You!

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