Where are the missing baryons?

Transcription

1 Interview of BSc dissertation Where are the missing baryons? Brandon Qiang Wang 6 th February 2018 Image from Millennium Simulation

2 Content I. Introduction II. Simulations III. Results IV. Conclusion 2

3 I. Introduction Image taken from slide by C.S. Frenk The theoretical prediction of baryon production is based on the Big Bang Nucleosynthesis (BBN). 3

4 Missing baryons Planck 2013 result Shull, Smith & Danforth 2012 A substantial fraction of baryons are missing! 4

5 Warm-Hot Intergalactic Medium (WHIM) Numerical simulations of the intergalactic medium have shown that at the present epoch, a significant fraction (40% 50%) of the baryonic component should be found in the ( T~10 6 K ) warm-hot intergalactic medium (WHIM). (Cen & Ostriker 2006) 5

6 II. Simulations Cosmological hydrodynamic simulations were carried out using GADGET-2. A few simplifications were assigned i.e. no galaxy formation & complicated astrophysical processes. Simulation L [h 1 Mpc] N [DM + gas] ε [h 1 kpc] m baryon [h 1 M ] Ω m Ω Λ n s Ω b H 0 σ 8 z start S S S Planck 2013 results S Computing power was provided by Microsoft Azure (4 Intel Xeon E v4 processors). S4 run took ~13 hours. 6

7 III. Results Movie I shows the evolution of WHIM colour-coded by density. Movie II shows the evolution of baryons colourcoded by temperature. Both are made from S4 run. 7

8 3D distribution S1 Run L = 50 h 1 Mpc N = 64 3 DM Hot WHIM Warm Baryon phases Hot: T > 10 7 K WHIM: 10 5 K < T < 10 7 K Warm: T < 10 5 K 8

9 3D distribution S2 Run L = 50 h 1 Mpc N = DM Hot WHIM Warm 9

10 3D distribution S3 Run L = 100 h 1 Mpc N = 64 3 DM Hot WHIM Warm 10

11 3D distribution S4 Run L = 100 h 1 Mpc N = DM Hot WHIM Warm WHIM follows dark matter and mainly resides in the cosmic web. Cen & Ostriker

12 Evolution of baryons S1 Run L = 50 h 1 Mpc N = 64 3 Mass fraction of WHIM at z = 0: 47 %. 12

13 Evolution of baryons S2 Run L = 50 h 1 Mpc N = Mass fraction of WHIM at z = 0: 48 %. 13

14 Evolution of baryons S3 Run L = 100 h 1 Mpc N = 64 3 Mass fraction of WHIM at z = 0: 41 %. 14

15 Evolution of baryons S4 Run L = 100 h 1 Mpc N = About half of the baryons exist as WHIM at present day. Cen & Ostriker 2006 Mass fraction of WHIM at z = 0: 45 %. 15

16 Formation of WHIM Closely connected to the gravitational growth of large-scale structure. Shock waves are produced when two collapsing perturbation meet and cross one another. Shock heating plays the major role in the formation of WHIM. Cen & Ostriker

17 Distribution of Gas S1 Run S2 Run 17

18 Distribution of Gas S3 Run S4 Run 18

19 Phase plane ρ < ρ b > = T S1 S3 S2 S4 Equation of state for WHIM ρ T Davé et al

20 Mass distribution ρ < ρ b > = Most of the mass of WHIM resides in the moderate overdensity range 10~300 with median value ~60. ρ = < ρ b > ρ < ρ b > = Cen & Ostriker

21 Observational implications Ultraviolet Observation X-ray Observation Sunyaev-Zel dovich effect 21

22 Observational efforts Graaff et al Submitted to Nature. 22

23 IV. Conclusion The missing baryon problem can be resolved with a cosmologically important component called Warm-Hot Intergalactic Medium (WHIM). The existence of WHIM is theoretically firm accounting for about half of baryonic content at z = 0. The primary mechanism is shock heating resulting in moderate overdensities. The detection of WHIM proposes significant difficulties. A bright future can be foreseen with the rapid development of observational techniques. 23

24 References (slides): Cen, R. & J. P. Ostriker 1999, The Astrophysical Journal, 514, 1. Cen, R. & J. P. Ostriker 2006, The Astrophysical Journal, 650, 560. Davé, R., et al. 2001, The Astrophysical Journal, 552, 473. Fukugita, M., C. J. Hogan & P. J. E. Peebles 1998, The Astrophysical Journal, 503, 518. de Graaff, A., Y.-C. Cai, C. Heymans & J. A. Peacock 2017, arxiv: Nicastro, F., et al. 2005, Nature, 433, nature Planck Collaboration 2014, Astronomy and Astrophysics, 571 Shull, J. M., B. D. Smith & C. W. Danforth 2012, The Astrophysical Journal, 759, 23. Steven, V. P., T. S. John & J. M. Shull 2004, The Astrophysical Journal Supplement Series, 152, 29. Tanimura, H., et al. 2017, ArXiv e-prints, 1709, arxiv: Slides by Carlos Frenk is available at GADGET-2 is available at A special webpage has been created to host all visualisation materials, which is available at Image from Millennium Simulation