Tomi Ylinen- The Cosmic Microwave Background

8/3/2019 Tomi Ylinen- The Cosmic Microwave Background

1/34

The Cosmic Microwave

Background

Tomi Ylinen

KTH/HIK

KTH 5A5461

Experimental Techniques in

Particle Astrophysics


2/34

Outline

Introduction

Theory

Detection

Case studies: COBE, WMAP

The future: Planck


3/34

Introduction

Why bother?

Measurements of the Cosmic Microwave Background (CMB)

allow for precise estimations of the age, composition and

geometry of the universe

What is the universe made of? How old is it? And where didobjects in the universe, including our planetary home, come

from?

T. Ylinen The Cosmic Microwave Background KTH 5A5461 1 October, 2007

Introduction

3/34


4/34

History

First discovered by Arno Penzias and Robert Wilson of AT&T BellLaboratories in 1965, when trying to remove a weird background noise

in their radio antenna (they

thought it was bird crap).

Received the Nobel Prizein 1978


Introduction

4/34

http://map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html


5/34

Once upon a time

Early universe

composed of a plasmaof charged particles

and photons

After 380 000 yearsof cooling, first atoms

formed and the

universe became

transparent to photons


Theory

5/34

W. Hu and M. J. White, "The Cosmic Symphony", Sci. Am., 290N2, (2004) 32


6/34

Mathematically speaking

The anisotropies in the CMB sky can be described by aspherical harmonic expansion

Observations can be divided into three categories:

Monopole (a00): the mean temperature of the CMB

Dipole (l=1): the anisotropy caused by the movement of thesolar system relative to the CMB

Higher-order multipoles (l2): anisotropy caused by

perturbations in density in the early Universe


Theory

6/34

,, lm

lmlmYaT


7/34

Mathematically speaking (2)

Many models of the early Universe say that the temperature

anisotropies should obey Gaussian statistics All statistical

properties of the temperature anisotropies can be computed from

a single function of multipole index l, the power spectrum

Thomson scattering of anisotropic radiation at last scattering gives

rise to ~5% polarization in the CMB This gives two measurable

quantities called the Stokes Q and U parameters These can be

decomposed into E- and B-type polarization patterns

The temperature anisotropies can then be characterized by four

power spectra CT, CE, CB and CTE


Theory

7/34


8/34

Monopole

Due to the expansion of the

universe, the photons have cooled

from an initial black-body

distribution at 3000 K to a present

value of about 2.725 0001 K

Measured using absolute

temperature devices


Theory

8/34

1

122

3

kT

hv

ec

hvvI

http://www.astro.ucla.edu/~wright/CMB.html


9/34

Dipole

Anisotropy with an amplitude of 3.358 0.017 mK,

caused by the fact that Earth, our Solar system and

Galaxy is moving relative to the CMB.

Can be used forcalibration


Theory

9/34

http://map.gsfc.nasa.gov/m_mm/ob_techcal.html


10/34

Higher-order multipoles

The temperature variance

as a function of the sizes

of the hot and cold spots,

i.e. the power spectrum,

fully characterizes the

anisotropies

From this plot a vast

variety of information

about the early universe

can be extracted

Measured using

differential temperature

devices


Theory

10/34

Fundamental

wave, largest

variations

Overtones Sharp cut-off

due to wave

dissipation

( < xmean)



11/34

Anisotropies

Inflation in combination with

quantum fluctuationstriggered soundwaves in the

primordial plasma, which

much like a musical

instrument had a

fundamental wave along witha series of overtones

After recombination, the

density anisotropies were

frozen into the cosmicmicrowave background

radiation


Theory

11/34



12/34

Detection

What do we want to detect? Temperature (energy) of the CMB

Anisotropies in the CMB temperature at different scales

Polarization of the CMB

How can we detect them?

Heterodyne detection

Incoherent detection

Detectors pointed in different directions

Polarization sensitive detectors


Detection

12/34


13/34

Heterodyne detection

A horn receiver working like an antennapicks up the radiation

The pulse is mixed with a

different frequency from a local oscillator

The output (IF = Intermediate Frequency)

is finally fed through a diode which converts

the pulse into a proportional voltage

Examples are Dicke-receivers (COBE) andHEMT-based (High Electron Mobility

Transistor) detectors (WMAP)


Detection

13/34

http://lambda.gsfc.nasa.gov/product/cobe/COBE_gallery.pdf


14/34

Incoherent detection

Consist of an absorber of heat capacity C,which is connected via a weak thermal link,

G, to a heat reservoir with a constant

temperature T0 Bolometer

The absorber is exposed to the power of

incoming light Psignal and a bias power Pbias.

The temperature of the absorber is then

T = T0 + (Psignal + Pbias)/G

The energy of an incoming photon is

determined by measuring the temperatureincrease it causes to the absorber.


Detection

14/34

http://www.planck.fr/article227.html

http://bolo.berkeley.edu/bolometers/introduction.html


15/34

Polarization

Polarization in the CMB can be measured using a polarization

sensitive bolometer, with two layers of absorbers corresponding to

perpendicular polarization directions


Detection

15/34

http://www.planck.fr/article228.html


16/34

Complications

ForegroundsMicrowave emission from our Galaxy andfrom extragalactic sources through

synchrotron, bremsstrahlung and dust

emission. Observations at several frequencies

enable separation

Secondary anisotropiesGravitational lensing, patchy reionization and the

Sunayaev-Zeldovich effect, i.e. Inverse Compton

scattering of the CMB photons by a hot electron gas,

which gives spectral distorsions

Higher-order statisticsMost of the CMB anisotropy information is contained in the power spectra, but weak signals are

present in higher-order statistics, which can measure any primordial non-Gaussianity in the

perturbations


Detection

16/34

http://www.rssd.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf


17/34

Case studies

Choosing to take a closer look at:COBE WMAP Planck

Other experiments:

ACBAR ACME/HACME ACT AMI AMiBA APACHE APEX ARCADE Archeops ARGO ATCA BAM BaR-SPOrt BEAST BICEP BIMA

BOOMERanG CAPMAP CAT CBI CG Clover COSMOSOMAS DASI

EBEX FIRS KUPID MAT MAXIMA MBI-B MINT MSAM PIQUE

POLAR POLARBeaR Polatron Python QMAP QMASK QuaD QUIET

RELIKT-1 SK SPOrt SPT SuZIE SZA Tenerife TopHat VSA


Case studies

17/34

C di


18/34

COBE

Operational 1989-1993

Carried three instruments:

FIRAS, DMR, DIRBE

Sensitivity T/T ~ 10-5

Angular resolution ~7

John Mather and

George Smootreceived the Nobel

Prize for this in 2006


18/34COsmic Background Explorer

Case studies

C t di


19/34

COBE instruments

Far Infrared Background Experiment (FIRAS)

A polarizing Michelson-interferometer, designed to obtain a precision

measurement between the CMB spectrum and a Planckian calibration

spectrum. The energy was measured by bolometric detectors.


19/34

Case studies


C t di


20/34

COBE instruments

Differential Microwave Radiometers (DMR)

Designed to detect the temperature

differences in the CMB. The receiver input

is alternately connected to two separate

antennas pointing in different directions

in the sky

If the two parts of the sky differ in

brightness, the signal will change when the

switch moves from one antenna to the other

To show that the differences come from the

sky and not from the differences in the

antennas, the whole apparatus is rotated


20/34

Case studies

Case studies


21/34

COBE instruments

Diffuse Infrared Background Experiment (DIRBE)

An off-axis Gregorian telescope, designed to make an

absolute measurement of the spectrum and angular

distribution of the diffuse infrared background.

The vibrating beam

interrupter allows for

continuous comparison

between the sky and a cold

zero-flux surface inside

the instrument


21/34

Case studies


Case studies


22/34

WMAP

Operational 2001-present

Carries dual back-to-back Gregorian telescopes

that feed 20 differential polarization sensitive

radiometers

Sensitivity T/T ~ 35 . 10-6

Angular resolution ~15

45 times better sensitivity

and 33 times better angularresolution than COBE


22/34Wilkinson Microwave Anisotropy Probe

Case studies

http://map.gsfc.nasa.gov/m_ig.html

Case studies


23/34

WMAP instruments

Basically the same

idea as in COBE


23/34

Case studies

Credit: WMAP

Case studies


24/34

Results so far

Anisotropy map after combining

the different frequencies and

thereby being able to

subtract the foreground

radiation (our Galaxy)

An example of a polarization

map measured at 23 GHz.

Color indicates strength.Most of the polarization

comes from our Galaxy


24/34

Case studies

http://map.gsfc.nasa.gov/m_mm.html

http://wmap.gsfc.nasa.gov/m_or.html

Case studies


25/34

Results so far (2)


25/34

Case studies


Case studies


26/34

Results so far (3)


26/34

Case studies

T

TE

E

B Average levelsfor foreground model

BB lensing signal

L. Page, et.al., Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis , ApJS, 170, (2007) 335

The future: Planck


27/34

The future: Planck

Planned launch in July 31, 2008 +

Will measure the anisotropies in the CMB with

unpresedented sensitivity (T/T ~ 2 10-6) and

angular resolution (5)


The future: Planck

27/34


http://astro.berkeley.edu/~mwhite/rosetta/node3.html#SECTION00030000000000000000

The future: Planck


28/34

Planck resolution


28/34

Simulated skymaps

5

5


The future: Planck


29/34

Planck resolution


29/34


The future: Planck


30/34

Instruments


30/34

An off-axis telescope with diameter1.5 m and two cryogenic instruments,

LFI and HFI, shielded by

baffles


The future: Planck


31/34

Planck LFI

An array of receivers basedon so-called HEMT amplifiers,

covering the frequency range

30-70 GHz and operating at

20 K

All LFI channels can

measure

polarization

and intensity


31/34


The future: Planck


32/34

Planck HFI


32/34

An array of receivers based on bolometers, covering the frequency range100-857 GHz and operating at 0.1 K

Four channels can

measure polarization


Summary


33/34

Summary

Accurate measurements of the Cosmic MicrowaveBackground can reveal a vast variety of properties about the

universe, such as the composition, age and geometry

To measure the tiny temperature variations, band filters,

interferometers, bolometers, transistors and diodes are used

The field is highly active, with successful experiments and

better ones coming up soon in the form of Planck


33/34

References


34/34

References34/34

Mission homepages

COBE http://lambda.gsfc.nasa.gov/product/cobe/

WMAP http://wmap.gsfc.nasa.gov/

Planck http://www.rssd.esa.int/index.php?project=Planck

Articles

W. Hu and M. J. White, "The Cosmic Symphony", Sci. Am., 290N2,

(2004) 32

W.-M. Yao, et al., "Review of Particle Physics", J. Phys. G33, (2006) 1

C.L. Bennett, et al., First Year Wilkinson Microwave Anisotropy

Probe (WMAP) Observations: Foreground Emission, ApJS, 148,

(2003) 97

G. Smoot, et al., COBE Differential Microwave Radiometers:

Instrument Design and Implementation, ApJ 360, (1990) 685-695

N. W. Boggess, et al., The COBE Mission: Its Design and

Performance Two Years after launch, ApJ 397, (1992) 420-429

L. Page, et.al., Three-Year Wilkinson Microwave Anisotropy Probe

(WMAP) Observations: Polarization Analysis , ApJS, 170, (2007) 335

Planck: The Scientific Programme, ESA-SCI(2005)1,http://www.rssd.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf

Books

M. Lachize-Rey & Edgard Gunzig, The Cosmological Background

Radiation, Cambridge University Press (1999)

C. H. Lineweaver et al., The Cosmic Microwave Background, NATO

ASI Series, Vol. 502, Kluwer Academic Publishers

Internet

http://bolo.berkeley.edu/bolometers/introduction.html

http://www.planck.fr/article227.htmlhttp://scienceworld.wolfram.com/physics/PlanckLaw.html

http://lambda.gsfc.nasa.gov/links/experimental_sites.cfm

http://astro.berkeley.edu/~mwhite/rosetta/

Documents

Tomi Ylinen- The Cosmic Microwave Background