- Email: [email protected]
Deuterium and big bang nucleosynthesis
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Nuclear Physics A663&664 (2000) 861e-864c
ELSEVIER
www.elsevier.nl/locate/npe
Deuterium and Big Bang Nucleosynthesis S. BurIes
a
"Department of Astronomy & Astrophysics, Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637 Measurements of deuterium absorption in high redshift quasar absorption systems provide a direct inference of the deuterium abundance produced by big bang nucleosynthesis (BBN). With measurements and limits from five independent absorption systems, we place strong constraints on the primordial ratio of deuterium to hydrogen, (D/H)p = 3.4 ± 0.3 x 10-5 [1,2]. We employ a direct numerical treatment to improve the estimates of critical reaction rates and reduce the uncertainties in BBN predictions of D/H and 7Li/H by a factor of three[3] over previous efforts[4]. Using our measurements of (D/H)p and new BBN predictions, we find at 95% confidence the baryon density Pb = (3.6 ± 0.4) x 10- 31 g cm-3 (nbh~5 = 0.045 ± 0.006 in units of the critical density), and cosmological baryon-photon ratio 7} = (5.1 ± 0.6) x 10- 1°.
1. Primordial Deuterium Of the light elements forged during the first 1000 seconds, the epoch of big bang nucleosynthesis, deuterium can provide the tightest constraints on models of BBN, as well as the cosmic baryon density [5,6]. Over the past five years, a great effort has been spent to identify, observe, and measure deuterium in high redshift, intergalactic clouds which exhibit absorption in the spectra of background QSOs. As explicitly stated last year by David Schramm[7], the new deuterium measurements will transform the area of big bang nucleosynthesis from a study in concordance to a study of precise predictions and powerful tests with other cosmological observations. An example of high-redshift deuterium absorption measured in the spectrum of QSO 1009+2956 is shown in Figure 1. The best fit model, including contamination from a nearby hydrogen absorber, gives D/H = 4.0~~:~ x 10- 5[2]. This result, combined with the tight constraints towards Q1937-1009[1], and upper limits towards four other QSOs[8-11] gives a primordial abundance of D/H = 3.4 ± 0.25 x 10- 5 .
2. Big Bang Nudeosynthesis To study BBN and the abundances of the light elements in the precision era, we need to characterize both the observational uncertainties and the uncertainties in calculating the BBN abundances. In the case of 4He, the weak rates dominate via the interconversion of protons and neutrons, and the significant effects have recently been studied in detail by Lopez et al[12]. The light nuclei reaction rates dominate the abundance uncertainties in 0375-9474/00/$ - see front matter © 2000 Elsevier Science RY. All rights reserved. PH S0375-9474(99)00732-0
862c
S. BurIes/Nuclear Physics A663&664 (2000) 86Ic-864c
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Figure 1. Lyman-a absorption of deuterium and hydrogen at redshift z = 2.504. The long dashed and dash-dotted curves show the composite best fit profiles of deuterium and hydrogen, respectively. The dotted curve shows a weak hydrogen absorber which is blended with the deuterium profile and is taken into account in the final model fit. The solid curve shows the best overall fit to the data (binned pixels). The short and tall tick marks show the line centers of the deuterium and hydrogen absorbers, respectively.
the other elements, and we have done a systematic study to quantify these uncertainties with a model-free approach[3]. The fundamental result is a reduction by factors of up to three in the uncertainties of deuterium and 7Li. The right panel in Figure 2 shows the contributions to the uncertainty in the deuterium abundance as a function of the one free parameter in standard BBN, 'T/: the baryon-to-photon ratio. The left panel is the standard "'T/" plot, which shows the primordial abundances as a function oi n. The thickness of the curves represents the 95% confidence range in our calculations. The vertical band shows the constraints imposed by the high-redshift deuterium measurements. The box overlapping the 4He curve shows the results of a recent study by Izotov & Thuan[13], who studied a large sample of metal-poor extragalactic H II regions to estimate the infer the primordial 4He abundance. The solid box overlapping 7Li shows plateau abundance of lithium in a sample of warm metal-poor halo stars. The dotted box shows the allowed range in primordial 7Li accounting for a possible factor of 2 depletion in these old halo
S. BurIes/Nuclear Physics A 663&664 (2000) 86Jc-864c
863c
stars. The leverage applied to BBN by the deuterium measurements can be seen directly by comparing the width of the vertical band to the widths of the boxes overlapping 4Heand 7Li. With the baryon density pinned down by deuterium, we can use the corresponding primordial abundances of 3He and 7Li as a zero point to trace the chemical evolution of these isotopes over the lifetime of the galaxy. In addition, the recently launched Far Ultraviolet Spectroscopic Explorer will effectively map the deuterium abundance of the interstellar medium, by observing hundreds of stars in the far UV. The distribution of deuterium in our galaxy will uncover the hidden story of star-formation and mixing in the Milky Way.
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Figure 2. (left) Updated predictions of the light element abundances in standard BBN. The width of the curves and boxes represent 95% confidence. The vertical band is the best constraint from high-redshift deuterium measurements. (right) Uncertainty contributions to the standard BBN predictions of deuterium. Each band represents 95% confidence, and the top band shows the cumulative uncertainty in all reactions. The dash-dotted line shows the previous estimate of 95% confidence. The error bar on the right represents the size of the current observational uncertainty at 95%.
864c
S. Buries /Nuclear Physics A663&664 (2000) 861c-864c
3. Conclusions Although there is much work still to be done on both the observational and theoretical sides of big bang nucleosynthesis, recent progress has placed OIl the threshold the "precision era" of BBN. The number of deuterium measurements at high-redshift should grow by a factor of 10, thanks to th e large sky surveys currently underway (2df QSO Redshift Survey in the south[16] and the SDSS in the north[17]) . A primordial deuterium abundance, together with a precise 4He abundance can const rain neutrino physics in the early universe[18 ,19]. In the standard model of BBN, we set the current limit of effective numb er of light neutrinos at 3.2[3]. The deuterium measurements pin down the presentday baryon density to an unprecedented 10%. This value will be compared dire ctl y to results of current and up coming cosmic microwave background (CMB) experiments and should be one of the strongest tests of the hot big bang cosmology. REFERENCES 1. S. Buries and D. Tytler, Astrophys. J. 499 (1998) 699. 2. S. Buries and D. Tytler, Astrophys. J. 507 (1998) 601. 3. S. Buries, K. M. Nollett, J. W. Truran, and M. S. Turner, Ph ys. Rev. Lett. 82 (1999) 4176. 4. M. S. Smith, L. H. Kawano , and R. A. Malaney, Astrophys. J. SIlPP. 85 (1993) 219. 5. G. M. Fuller and C. Y. Cardall, Nucl, Phys. B. 51 (1996) 71. 6. D. N. Schramm and M. S. Turner, Rev. Mod. Ph ys. 70 (1998) 303. 7. D. N. Schramm, Space Sci. Rev. 84 (1998) 3. 8. D. Tytler, S. Buries, L. Lu, X-M . Fan , A. M. Wolfe, and B. D. Savage, Astronom . J. 117 (1999) 63. 9. D. Kirkman, D. Tytler, S. Burles , D. Lubin, and J. M. O'Meara, Astrophys. J . in press . 10. P. Molaro , P. Bonifacio, M. Centurion, and G. Vladilo , Astron & Astrophys. Lett. in press. 11. S. Burle s, D. Kirkman, and D. Tytler, Astrophys. J. 519 (1999) 18. 12. R. E. Lopez , M. S. Turner, and G. Gyuk , Phys. Rev. D. 56 (1997) 3191. 13. Y. 1. Izotov and T . X. Thuan, Astrophys. J. 500 (1998) 188. 14. P. Bonifacio and P. Molaro , Mon. Not. R. astron . Soc. 285 (1997) 847. 15. A. Vidal-Madjar, F. Roger, M. Lemoine, and the FUSE team, Proc of the 13th lAP Col!. Editions Frontieres (1997) 355. 16. B. J . Boyle, S. M. Croom, R. J. Smith, T. Shanks, L. Miller, and N. Loaring, Looking Deep in the Southern Sky, ed. R. Marganti and W. J . Couch , Springer-Verlag (1999). 17. X. Fan , and the SDSS collaboration, Astronom. J ., in press. 18. G. St eigman , D. N. Schramm, and J. E. Gunn, Phys . Lett. B. 66 (1977) 262. 19. X. Shi and G. M. Fuller , Phys. Rev D. 59 (1999) 063006.
WM ~
Nuclear Physics A663&664 (2000) 861e-864c
ELSEVIER
www.elsevier.nl/locate/npe
Deuterium and Big Bang Nucleosynthesis S. BurIes
a
"Department of Astronomy & Astrophysics, Enrico Fermi Institute, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637 Measurements of deuterium absorption in high redshift quasar absorption systems provide a direct inference of the deuterium abundance produced by big bang nucleosynthesis (BBN). With measurements and limits from five independent absorption systems, we place strong constraints on the primordial ratio of deuterium to hydrogen, (D/H)p = 3.4 ± 0.3 x 10-5 [1,2]. We employ a direct numerical treatment to improve the estimates of critical reaction rates and reduce the uncertainties in BBN predictions of D/H and 7Li/H by a factor of three[3] over previous efforts[4]. Using our measurements of (D/H)p and new BBN predictions, we find at 95% confidence the baryon density Pb = (3.6 ± 0.4) x 10- 31 g cm-3 (nbh~5 = 0.045 ± 0.006 in units of the critical density), and cosmological baryon-photon ratio 7} = (5.1 ± 0.6) x 10- 1°.
1. Primordial Deuterium Of the light elements forged during the first 1000 seconds, the epoch of big bang nucleosynthesis, deuterium can provide the tightest constraints on models of BBN, as well as the cosmic baryon density [5,6]. Over the past five years, a great effort has been spent to identify, observe, and measure deuterium in high redshift, intergalactic clouds which exhibit absorption in the spectra of background QSOs. As explicitly stated last year by David Schramm[7], the new deuterium measurements will transform the area of big bang nucleosynthesis from a study in concordance to a study of precise predictions and powerful tests with other cosmological observations. An example of high-redshift deuterium absorption measured in the spectrum of QSO 1009+2956 is shown in Figure 1. The best fit model, including contamination from a nearby hydrogen absorber, gives D/H = 4.0~~:~ x 10- 5[2]. This result, combined with the tight constraints towards Q1937-1009[1], and upper limits towards four other QSOs[8-11] gives a primordial abundance of D/H = 3.4 ± 0.25 x 10- 5 .
2. Big Bang Nudeosynthesis To study BBN and the abundances of the light elements in the precision era, we need to characterize both the observational uncertainties and the uncertainties in calculating the BBN abundances. In the case of 4He, the weak rates dominate via the interconversion of protons and neutrons, and the significant effects have recently been studied in detail by Lopez et al[12]. The light nuclei reaction rates dominate the abundance uncertainties in 0375-9474/00/$ - see front matter © 2000 Elsevier Science RY. All rights reserved. PH S0375-9474(99)00732-0
862c
S. BurIes/Nuclear Physics A663&664 (2000) 86Ic-864c
III
IIII
II
1
><
;:l
~ '0
Q)
.~
'iii 0.5
E o
z
ol=========~--_-.a..i=:.=========j Ly-ex
4256
4258
4260
4262
4264
Wavelength(!)
Figure 1. Lyman-a absorption of deuterium and hydrogen at redshift z = 2.504. The long dashed and dash-dotted curves show the composite best fit profiles of deuterium and hydrogen, respectively. The dotted curve shows a weak hydrogen absorber which is blended with the deuterium profile and is taken into account in the final model fit. The solid curve shows the best overall fit to the data (binned pixels). The short and tall tick marks show the line centers of the deuterium and hydrogen absorbers, respectively.
the other elements, and we have done a systematic study to quantify these uncertainties with a model-free approach[3]. The fundamental result is a reduction by factors of up to three in the uncertainties of deuterium and 7Li. The right panel in Figure 2 shows the contributions to the uncertainty in the deuterium abundance as a function of the one free parameter in standard BBN, 'T/: the baryon-to-photon ratio. The left panel is the standard "'T/" plot, which shows the primordial abundances as a function oi n. The thickness of the curves represents the 95% confidence range in our calculations. The vertical band shows the constraints imposed by the high-redshift deuterium measurements. The box overlapping the 4He curve shows the results of a recent study by Izotov & Thuan[13], who studied a large sample of metal-poor extragalactic H II regions to estimate the infer the primordial 4He abundance. The solid box overlapping 7Li shows plateau abundance of lithium in a sample of warm metal-poor halo stars. The dotted box shows the allowed range in primordial 7Li accounting for a possible factor of 2 depletion in these old halo
S. BurIes/Nuclear Physics A 663&664 (2000) 86Jc-864c
863c
stars. The leverage applied to BBN by the deuterium measurements can be seen directly by comparing the width of the vertical band to the widths of the boxes overlapping 4Heand 7Li. With the baryon density pinned down by deuterium, we can use the corresponding primordial abundances of 3He and 7Li as a zero point to trace the chemical evolution of these isotopes over the lifetime of the galaxy. In addition, the recently launched Far Ultraviolet Spectroscopic Explorer will effectively map the deuterium abundance of the interstellar medium, by observing hundreds of stars in the far UV. The distribution of deuterium in our galaxy will uncover the hidden story of star-formation and mixing in the Milky Way.
025 0.24
0.23
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-
-
- - - -
-
- - - - - -
--
- - - - - - -
- - - -
-
-
- -
7]
-~-~- --
-
o
oI
--
N
oI
:...--- -
--- - - - -
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-
f--
0.22
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--- .- - - .-
I 10
71 10
Figure 2. (left) Updated predictions of the light element abundances in standard BBN. The width of the curves and boxes represent 95% confidence. The vertical band is the best constraint from high-redshift deuterium measurements. (right) Uncertainty contributions to the standard BBN predictions of deuterium. Each band represents 95% confidence, and the top band shows the cumulative uncertainty in all reactions. The dash-dotted line shows the previous estimate of 95% confidence. The error bar on the right represents the size of the current observational uncertainty at 95%.
864c
S. Buries /Nuclear Physics A663&664 (2000) 861c-864c
3. Conclusions Although there is much work still to be done on both the observational and theoretical sides of big bang nucleosynthesis, recent progress has placed OIl the threshold the "precision era" of BBN. The number of deuterium measurements at high-redshift should grow by a factor of 10, thanks to th e large sky surveys currently underway (2df QSO Redshift Survey in the south[16] and the SDSS in the north[17]) . A primordial deuterium abundance, together with a precise 4He abundance can const rain neutrino physics in the early universe[18 ,19]. In the standard model of BBN, we set the current limit of effective numb er of light neutrinos at 3.2[3]. The deuterium measurements pin down the presentday baryon density to an unprecedented 10%. This value will be compared dire ctl y to results of current and up coming cosmic microwave background (CMB) experiments and should be one of the strongest tests of the hot big bang cosmology. REFERENCES 1. S. Buries and D. Tytler, Astrophys. J. 499 (1998) 699. 2. S. Buries and D. Tytler, Astrophys. J. 507 (1998) 601. 3. S. Buries, K. M. Nollett, J. W. Truran, and M. S. Turner, Ph ys. Rev. Lett. 82 (1999) 4176. 4. M. S. Smith, L. H. Kawano , and R. A. Malaney, Astrophys. J. SIlPP. 85 (1993) 219. 5. G. M. Fuller and C. Y. Cardall, Nucl, Phys. B. 51 (1996) 71. 6. D. N. Schramm and M. S. Turner, Rev. Mod. Ph ys. 70 (1998) 303. 7. D. N. Schramm, Space Sci. Rev. 84 (1998) 3. 8. D. Tytler, S. Buries, L. Lu, X-M . Fan , A. M. Wolfe, and B. D. Savage, Astronom . J. 117 (1999) 63. 9. D. Kirkman, D. Tytler, S. Burles , D. Lubin, and J. M. O'Meara, Astrophys. J . in press . 10. P. Molaro , P. Bonifacio, M. Centurion, and G. Vladilo , Astron & Astrophys. Lett. in press. 11. S. Burle s, D. Kirkman, and D. Tytler, Astrophys. J. 519 (1999) 18. 12. R. E. Lopez , M. S. Turner, and G. Gyuk , Phys. Rev. D. 56 (1997) 3191. 13. Y. 1. Izotov and T . X. Thuan, Astrophys. J. 500 (1998) 188. 14. P. Bonifacio and P. Molaro , Mon. Not. R. astron . Soc. 285 (1997) 847. 15. A. Vidal-Madjar, F. Roger, M. Lemoine, and the FUSE team, Proc of the 13th lAP Col!. Editions Frontieres (1997) 355. 16. B. J . Boyle, S. M. Croom, R. J. Smith, T. Shanks, L. Miller, and N. Loaring, Looking Deep in the Southern Sky, ed. R. Marganti and W. J . Couch , Springer-Verlag (1999). 17. X. Fan , and the SDSS collaboration, Astronom. J ., in press. 18. G. St eigman , D. N. Schramm, and J. E. Gunn, Phys . Lett. B. 66 (1977) 262. 19. X. Shi and G. M. Fuller , Phys. Rev D. 59 (1999) 063006.