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THE NITROGEN ISOTOPE RATIO IN DENSE MOLECULAR CLOUDS Gilles Adande Lucy M. Ziurys Department of Chemistry, Department of Astronomy, Steward Observatory.

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Presentation on theme: "THE NITROGEN ISOTOPE RATIO IN DENSE MOLECULAR CLOUDS Gilles Adande Lucy M. Ziurys Department of Chemistry, Department of Astronomy, Steward Observatory."— Presentation transcript:

1 THE NITROGEN ISOTOPE RATIO IN DENSE MOLECULAR CLOUDS Gilles Adande Lucy M. Ziurys Department of Chemistry, Department of Astronomy, Steward Observatory and Arizona Radio Observatory University of Arizona

2 Big Bang nucleosynthesis 1 H, 2 H, 3 He, 4 He Stellar nucleosynthesis 12 C, 14 N, …., 56 Fe Supernova nucleosynthesis ≥ 56 Fe Cosmic rays spallation 3 Li, 4 Be, 5 B Isotope ratios diagnostic tool for nucleosynthesis processes, distribution of star masses…

3 14 N/ 15 N variations understanding solar systems evolution

4 Arpigny et al, science, N/ 15 N across our Solar System

5 14 N/ 15 N estimation Dust extinction at galactic center  Millimeter wave astronomy primary method Challenges & Difficulties N 2 no dipole moment N + or N high energy spectra Possible fractionation for observable species: HCN, HNC, N 2 H +, CN, NH 3, HC 3 N… Main isotope large optical depth  estimation of abundances problematic Existing studies methodology: double isotope ratio Rarer 15 N isotope, long integration time for good signal to noise 14 N 15 N 13 C 12 C ×= 13 C 15 N

6 Few galactic studies Large uncertainties ( > 50 %) 14 N/ 15 N range Dahmen et al, A&A, 1994 Milam et al, ApJ, 2005

7 HNC probe molecule Comparisons with HCN studies Main isotope moderately thick Rarer isotope observable reasonable observing time Limited fractionation Terzieva & Herbst, MNRAS, 2000 Our study

8 ARO 12 m and SMT telescope ALMA type Band 3 receiver ( GHz) ALMA type Band 6 ( GHz) 12 m at Kitt Peak SMT on Mt Graham

9 SpeciesFrequency (MHz) Transition J ′  J cc HNC   HN 13 C    H 15 NC   Source Distance to GC (kpc) Sgr B2(2N)0.1 W313.1 G M17-SW6.1 W51M6.1 DR Orion Bar8.3 Orion-KL8.3 NGC W3 (OH)9.6 S DR-21

10 Example spectra toward NGC 7538 HN 13 C H 15 NC = 5.4 ± N 15 N = 302 ± 74 Using 12 C/ 13 C from CN:

11 direct measurement for NGC 7538 with HCN Hyperfine lines follow LTE spin statistics  Transition optically thin H 13 CN H 13 C 15 N = 215 ± 61 Existing studies: 14 N 15 N = 463 ± N 15 N = 302 ± 74 Using 12 C/ 13 C from CN:

12 14 N/ 15 N for 11 molecular clouds Conclusions: Galactic gradient Values smaller than previous estimations 14 N/ 15 N ~ For HNC in local ISM 14 N/ 15 N ~ Close to comets measurements 14 N/ 15 N = 18.0 (9.8) × D gc (72.4)

13 Future Future directions Increase S/N Expand survey to more clouds Direct measurement with LVG modeling Evaluate fractionation with mapping observations of 14 N/ 15 N in Orion

14 Acknowledgements Professor Lucy Ziurys Dr. Stefanie Milam Dr. DeWayne Halfen, Dr. Emmy Tenenbaum, Lindsay Zack, Jessica Dodd, Ming Sun, Matthew Bucchino, Jie Min, Robin Pulliam, Brent Harris Funding: NASA-NSF


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