dark matter and cosmic structure formation -...

Dark Matter and Cosmic Structure Formation

Prof. Luke A. CorwinPHYS 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

Outline

1 Belated Introductions

2 Big Bang and ΛCDM

3 Galaxy and Cluster Formation

4 CMB measurements

5 Reminders


Belated Introductions

Travel Odditities

Since I was in Japan for most of January, this (barring anyunexpected problems) is the first class with the instructor of thiscourse. Most of these slides were written aboard Delta 622(Boeing 777, 10666 m above Canada) and in the Minneapolis-St.Paul airport. Now that I am back, I would like to meet you andintroduce myself.

Belated Introductions

As most of you know, I am Luke Corwin. My researchinterests are in neutrinos, and I am currently part of theNOvA and LBNE collaborations. This dark matter class is asmuch 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?


Big Bang and ΛCDM

What do you know about the BigBang Theory1 and the ΛCDM

model?

1Not the TV showL. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 4 / 14

Big Bang and ΛCDM

The Big Bang Theory

Proposed by Catholic priest and astronomer GerogesLemaıtre2

The universe began in an extremely hot and dense state (a“primeval atom” according to Lemaıtre) that has beenexpanding and cooling for3 13.81± 0.05 Gyr

The universe has a critical energy density ρcrit = 3H20/(8πG),

where H0 is the present expansion rate of the Universe(usually given in km · s−1 ·Mpc−1).4

For true ρ < ρcrit, the Universe is open and expands forever;for ρ > ρcrit, the Universe will stop expanding and collapse.

2Nature 128, 699; Nature 127, 7063Planck Collaboration, arXiv:1303.50764PDG


arXiv:1303.5076

Big Bang and ΛCDM

Standard Cosmological Model (ΛCDM)

Figure : ESA/Planck

Named in analogy to theStandard Model of ParticlePhysics

Λ = cosmological constantor dark energy

CDM = Cold(non-relativistic) DarkMatter

Currently our best model ofthe content, structure, andhistory of the materialuniverse


Big Bang and ΛCDM

Cosmological Variable Definitions

Ωi ≡ ρi/ρcrit, 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(H0 = 100h km · s−1 ·Mpc−1)

σ8 = fluctuation amplitude at 8h−1 Mpc scale

Ωih2 is measured by Planck in the CMB fits.

Current Measurements a

aPDG; Planck Collaboration, arXiv:1303.5076

h = 0.673± 0.012

σ8 = 0.828± 0.012

Ωb = 0.0499± 0.0022

A statistically significant ΩDM 6= 0 is evidence for dark matter


arXiv:1303.5076

Galaxy and Cluster Formation

We Want to Understand Cosmic Structure

Slices through theSDSS 3-dimensionalmap of the distributionof galaxies. Earth is atthe center, and eachpoint represents agalaxy (M. Blanton andthe Sloan Digital SkySurvey)



Numerical simulations

As with many N-body problems, numerical simulations areused 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 acubic region of 4.11 Gpc (3h−1Gpc) on a side. The darkmatter distribution is represented by67203 = 303, 464, 448, 000 particles. Its particle mass ismp = 8.456× 109 M.

5arXiv:1203.3216L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 9 / 14

arXiv:1203.3216


The mass densityfield in theMillennium-XXLfocusing on themost massive halopresent in thesimulation at z=0.Each inset zoomsby a factor of 8from the previousone. As you cansee, we havequalitativeagreementbetween thestructure here andin the SDSS data.



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 quantifiesnumber of large halos, which is correlated withΩm = ΩCDM + Ωb

The Planck Collaboration studied 189 galaxy clusters; basedon their luminosity distributions, they measuredσ8(Ωm/0.27)0.3 = 0.782± 0.010

ΩCDM = 0⇒ σ8(Ωm/0.27)0.3 = 0.17


CMB measurements

Figure : We observe small scale (10−5) variations on the cosmicmicrowave background. This represent density fluctuations in thebaryonic matter of the early universe, which were seeds of the currentstructure of the cosmos


CMB measurements

0.

700.

750.

800.

850.

900.

95

m8(1

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.27)

0.3

WL*

X-rays*

MaxBCG*

ACT

SPTPlanck

Planck

SPT

WMAP

Clusters CMBLSSComparison ofmultiplemethods formeasuringσ8(Ωm/0.27)0.3,including thePlanckmeasurementsof galaxyclusters and theCMB. AllassumeΩΛ + ΩM = 1,which isconsistent withmeasurementsa.

aarXiv:1303.5080L. Corwin, PHYS 792 (SDSM&T) DM & Cosmic Structure Jan. 23, 2014 (W2-2) 13 / 14

arXiv:1303.5080

Reminders

Reminders

Choose your topic for mid-term presentation before Jan. 30

Presentations will be given (two per class period) duringWeek 7 (Feb. 25 and 27)The first person to inform me of their topic choice will havetheir 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 thesemester we will be in CB 110, except February 27 and April3, when we will be back in CB 108.


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