1. Chemical evolution of N2H+ in massive star-forming regions
喻耐平
王俊杰 徐金龙
July 2018 Kunming
中德亚毫米波望远镜

2. Content 1. Massive star formation 2. Properties of N2H+
3. Data analysis
4. Summary
5. Subsequent work

3. Massive star formation
IRDCs(starless cores)
Hot cores
HII regions
O B clusters

4. Massive star formation
恒星演化
物理环境
化学性质

5. Properties of N2H+
Trace dense and cold gas
+ N
Caselli et al. 1995

6. Properties of N2H+ Lee et al. (2004):
Bonner-Ebert sphere + inside-outside collapse
Formation:
H3+ + N2 → N2H+ + H2
Destroy(T > 20K):
N2H+ + CO → HCO+ + N2

7. Properties of N2H+ N2H+ + e- → N2 + H or NH (Vigren et al. 2012)
Yu et al MNRAS
Yu et al ApJ

8. Properties of N2H+ X(N2H+) Tdust ~20 K ~30 K Early stage Middle stage
Late stage
Tdust

9. Data analysis Data set: 1. MALT90 (~90 GHz)
2. Hi-GAL (70, 160, 250, 350, and 500 μm)

10. Data analysis Molecular data: MALT90 (Foster et al. 2011)
From MALT90 home page

11. Data analysis
N2H+ (1-0)
N2H+ (1-0)

12. Data analysis
CN148

13. Data analysis
S36

14. Data analysis G

15. Data analysis G

16. Data analysis
SED method using Hi-GAL (70, 160, 250, 350, and 500 μm): (Wang et al MNRAS)
1. Remove the background emissions;
2. smooth and rebin to the beam and pixel sizes of 500 μm;
3. SED
N(H2)
Tdust
Where ,

17. Data analysis
SED result:
N(H2)
Tdust

18. Data analysis
N(H2)
Tdust
Abundance map

19. Data analysis

20. Data analysis
Tdust ~ 27 K

21. Data analysis
Compared with chemical models of low-mass star formation:
X(N2H+)
~20 K
~30 K
Early stage
Middle stage
Late stage
Tdust

22. Higher resolution observations are needed!
Data analysis
Three reasons:
1. Beam dilution;
core: ~0.1 pc clump: ~1 pc
2. Chemical model may be not accurate;
3. Massive star formation process.
Higher resolution observations are needed!

23. Summary 1. A method to study chemical properties;
2. When the dust temperature is below 27 K, the abundance of N2H+ increases with dust temperature;
3. When the dust temperature is above 27 K, the abundance of N2H+ begins to drop.

24. Subsequent work
HC3N
C2H

25. The end Thanks