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, 2003 14 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 200-800 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 (84-116 GHz) ALMA type Band 6 (211-275 GHz) 12 m at Kitt Peak SMT on Mt Graham

9. SpeciesFrequency (MHz) Transition J ′  J cc HNC 90663.6 1  0 0.88 271981.0 3  2 0.75 HN 13 C 87090.8 1  0 0.88 174179.4 2  1 0.69 261263.3 3  2 0.75 H 15 NC 88865.7 1  0 0.88 266587.8 3  2 0.75 Source Distance to GC (kpc) Sgr B2(2N)0.1 W313.1 G34.35.1 M17-SW6.1 W51M6.1 DR-218.0 Orion Bar8.3 Orion-KL8.3 NGC75388.9 W3 (OH)9.6 S15610.9 DR-21

10. Example spectra toward NGC 7538 HN 13 C H 15 NC = 5.4 ± 0.9 14 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 ± 102 14 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 ~ 100-500 For HNC in local ISM 14 N/ 15 N ~ 150-300 Close to comets measurements 14 N/ 15 N = 18.0 (9.8) × D gc + 92.4 (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