Dark Matter and Cosmic Structure Formation

Transcription

1 Dark Matter and Cosmic Structure Formation Prof. Luke A. Corwin PHYS 792 South Dakota School of Mines & Technology Jan. 23, 2014 (W2-2) L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 1 / 14

2 Outline 1 Belated Introductions 2 Big Bang and ΛCDM 3 Galaxy and Cluster Formation 4 CMB measurements 5 Reminders L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 2 / 14

3 Belated Introductions Travel Odditities Since I was in Japan for most of January, this (barring any unexpected problems) is the first class with the instructor of this course. Most of these slides were written aboard Delta 622 (Boeing 777, m above Canada) and in the Minneapolis-St. Paul airport. Now that I am back, I would like to meet you and introduce myself. Belated Introductions As most of you know, I am Luke Corwin. My research interests are in neutrinos, and I am currently part of the NOvA and LBNE collaborations. This dark matter class is as much a chance for me to learn about the subject as you. Could you each tell me your name, your research interests, and why you decided to take this class? L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 3 / 14

4 Big Bang and ΛCDM What do you know about the Big Bang Theory 1 and the ΛCDM model? 1 Not the TV show L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 4 / 14

5 Big Bang and ΛCDM The Big Bang Theory Proposed by Catholic priest and astronomer Geroges Lemaître 2 The universe began in an extremely hot and dense state (a primeval atom according to Lemaître) that has been expanding and cooling for ± 0.05 Gyr The universe has a critical energy density ρ crit = 3H 2 0/(8πG), where H 0 is the present expansion rate of the Universe (usually given in km s 1 Mpc 1 ). 4 For true ρ < ρ crit, the Universe is open and expands forever; for ρ > ρ crit, the Universe will stop expanding and collapse. 2 Nature 128, 699; Nature 127, Planck Collaboration, arxiv: PDG L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 5 / 14

6 Big Bang and ΛCDM Standard Cosmological Model (ΛCDM) Figure : ESA/Planck Named in analogy to the Standard Model of Particle Physics Λ = cosmological constant or dark energy CDM = Cold (non-relativistic) Dark Matter Currently our best model of the content, structure, and history of the material universe L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 6 / 14

7 Big Bang and ΛCDM Cosmological Variable Definitions Ω i ρ i /ρ crit, where i can be dark energy Λ, CDM or DM, γ, ν, all matter (M), baryonic matter (b), etc. h is the scale factor for the Hubble expansion rate (H 0 = 100h km s 1 Mpc 1 ) σ 8 = fluctuation amplitude at 8h 1 Mpc scale Ω i h 2 is measured by Planck in the CMB fits. Current Measurements a a PDG; Planck Collaboration, arxiv: h = ± σ 8 = ± Ω b = ± A statistically significant Ω DM 0 is evidence for dark matter L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 7 / 14

8 Galaxy and Cluster Formation We Want to Understand Cosmic Structure Slices through the SDSS 3-dimensional map of the distribution of galaxies. Earth is at the center, and each point represents a galaxy (M. Blanton and the Sloan Digital Sky Survey) L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 8 / 14

9 Galaxy and Cluster Formation Numerical simulations As with many N-body problems, numerical simulations are used to understand the gravitational interactions and results. Usually, a cube of space is simulated using large numbers of particles An example of a high resolution simulation is he Millennium-XXL Simulation (MXXL) 5, which simulates a cubic region of 4.11 Gpc (3 h 1 Gpc) on a side. The dark matter distribution is represented by = 303, 464, 448, 000 particles. Its particle mass is m p = M. 5 arxiv: L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 9 / 14

10 Galaxy and Cluster Formation The mass density field in the Millennium-XXL focusing on the most massive halo present in the simulation at z=0. Each inset zooms by a factor of 8 from the previous one. As you can see, we have qualitative agreement between the structure here and in the SDSS data. L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 10 / 14

11 Galaxy and Cluster Formation Quantitative Measurements with Galaxy Clusters Two Kinds of DM Structures Halos are gravitationally bound and usually ellipsoidal. Galaxies form within them Streams are not gravitationally bound Counting galaxy clusters at different redshifts quantifies number of large halos, which is correlated with Ω m = Ω CDM + Ω b The Planck Collaboration studied 189 galaxy clusters; based on their luminosity distributions, they measured σ 8 (Ω m /0.27) 0.3 = ± Ω CDM = 0 σ 8 (Ω m /0.27) 0.3 = 0.17 L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 11 / 14

12 CMB measurements Figure : We observe small scale (10 5 ) variations on the cosmic microwave background. This represent density fluctuations in the baryonic matter of the early universe, which were seeds of the current structure of the cosmos L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 12 / 14

13 CMB measurements ( /0.27) M LSS WL* MaxBCG* X-rays* ACT SPT Clusters Planck CMB Planck SPT WMAP Comparison of multiple methods for measuring σ 8 (Ω m /0.27) 0.3, including the Planck measurements of galaxy clusters and the CMB. All assume Ω Λ + Ω M = 1, which is consistent with measurements a. a arxiv: L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 13 / 14

14 Reminders Reminders Choose your topic for mid-term presentation before Jan. 30 Presentations will be given (two per class period) during Week 7 (Feb. 25 and 27) The first person to inform me of their topic choice will have their choice of presentation date. Choose your topic for final presentation on or before Feb. 20 Since we have no USD students, for most of the rest of the semester we will be in CB 110, except February 27 and April 3, when we will be back in CB 108. L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 14 / 14