slide1 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Observational Cosmology Roger Emery, Space Science & Technology Dept, RAL. (r.j.emery@rl.ac.uk) PowerPoint Presentation
Download Presentation
Observational Cosmology Roger Emery, Space Science & Technology Dept, RAL. (r.j.emery@rl.ac.uk)

Loading in 2 Seconds...

play fullscreen
1 / 52

Observational Cosmology Roger Emery, Space Science & Technology Dept, RAL. (r.j.emery@rl.ac.uk) - PowerPoint PPT Presentation


  • 150 Views
  • Uploaded on

Observational Cosmology Roger Emery, Space Science & Technology Dept, RAL. (r.j.emery@rl.ac.uk) (with acknowledgement to Dr M. Griffin at Queen Mary College for many figures). AIM - Give an overview of observational cosmology - Look at current work - What’s coming in the future

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Observational Cosmology Roger Emery, Space Science & Technology Dept, RAL. (r.j.emery@rl.ac.uk)' - elina


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Observational Cosmology

Roger Emery, Space Science & Technology Dept, RAL. (r.j.emery@rl.ac.uk)

(with acknowledgement to Dr M. Griffin at Queen Mary College for many figures)

AIM

- Give an overview of observational cosmology

- Look at current work

- What’s coming in the future

A. What sort of measurements have cosmological significance?

B. What kinds of practical problems and technologies are involved?

C. Some key observations.

slide2

A. What sort of measurements have cosmological significance?

- Measurements of the distance scale of sources / the Universe.

- Large scale structure

- Source counts versus ‘distance’

- Stellar and galactic evolution.

- Abundance of the elements.

- Cosmic Microwave Background.

- The mass of galaxies / in the Universe

- Particle accelerators and the structure of matter.

slide4

1. Parallax (Using the orbit of the Earth around the Sun as a baseline).

* PARSEC(pc) - distance at which a star would have a parallax of 1 arc second

= 3.1x1016metres  3.26 light years.

- Primary observations allowed  1000 stars to be measured, including  Centauri (1.3pc)

- Hipparcos (ESA) satellite: Accuracy of parallax measurement  1 milli arcsec so has measured out to 1000pc (1kpc).

Compare Orion region at 1.5 kpc, Galactic centre at 8 kpc

or LMC at 55 kpc, Andromeda at 770 kpc - Local group of galaxies

- New proposals for satellites, e.g. GAIA, aiming for few micro arcsec.

2. Standard Candles.

- Cepheid variable stars

- Takes measurements to limits of the Local Supercluster and beyond (~ 15Mpc)

- Novae

- Supernovae etc.

the hubble parameter h

Speed = H x Distance

60,000

Speed of recession (v) (km/second)

40,000

20,000

0

3000

4000

1000

2000

Distance (Millions light years)

THE HUBBLE PARAMETER, H

How fast is the expansion today?

Z=0.25

H = 40 - 80 km/s/Mpc

1227Mpc

How long since the

big bang?

10 - 15 billion years

Red shift (z) = /o , [ 1+z = (1+v/c)/(1-(v/c)2 )1/2 ] therefore z  v/c

star forming clouds shine mainly in the far infrared

Massive hot stars (20–50,000 K)

form in the cloud and emit mainly

UV radiation ( ~ 0.1 - 0.3 m)

The UV radiation is absorbed by dust grains in the cloud

The grains are warmed up to about 40 K and re-emit the energy as far infrared radiation ( ~ 50 - 100 m)

1. Galactic and stellar evolution

STAR-FORMING CLOUDS SHINE MAINLY IN THE FAR INFRARED
typical spectra of nearby starburst galaxies

Optical/Near- Infrared

Far infrared

13

12

11

Luminosity (L)

10

9

8

7

0.1

1

10

100

1000

Wavelength (m)

Observing and understanding Galactic emission.

TYPICAL SPECTRA OF NEARBY STARBURST GALAXIES
redshifted spectra of starburst galaxies

10

102L

Z = 0.1

1

0.5

0.1

Flux density (Jy)

1

3

0.01

5

0.001

0.0001

10

100

1,000

10,000

l(mm)

REDSHIFTED SPECTRA OF STARBURST GALAXIES
star formation history of the universe

No correction for dust extinction

Star-formation rate

Extinction corrected

Redshift

STAR-FORMATION HISTORY OF THE UNIVERSE

Optical and UV measurements

the cosmic microwave background

Universe was opaque before recombination

Last scattering surface

T ~ 300,000 yrsz ~ 1000

z ~ 5

Today

qHorizon  2o

Typical CBRphoton

Less dense than average

More dense than average

Hot spot

Cold spot

The Cosmic Microwave Background

Big Bang

the density parameter

 < 1

Negativecurvature

Distance

 = 1

Flat

 > 1

Positivecurvature

Time

The Amount of Matter in Galaxies and the Universe

THE DENSITY PARAMETER, 

Current evidence:  is between 0.3 and 2

what do astronomers want to measure
WHAT DO ASTRONOMERS WANT TO MEASURE?

INTENSITY of electromagnetic radiation, as a function of :

FREQUENCY - Photometry, Spectroscopy

POSITIONon the sky - Imaging

TIME - Variability

POLARISATION - Polarimetry

Sensitivity: as high as possible

Angular (spatial) resolution: Good enough to resolve interesting spatial details of the source(s)

Spectral (wavelength) resolution: Good enough to resolve details and features of the spectral distribution of the source intensity

Wavelength coverage: Wide enough to take in all parts of the spectrum that contain useful information

observational requirements for studying galaxy formation

OBSERVATIONAL REQUIREMENTS FOR STUDYING GALAXY FORMATION

• Very high sensitivity – objects are at immense distances

• Good angular resolution to avoid confusion (overlapping sources)

• Observations at different wavelengths

• Optical/NIR: source positions and redshifts, galaxy type, chemistry, etc. (HST, NGST, large ground-based telescopes)

• FIR-mm: re-processed and redshifted UV (FIRST, SCUBA, Millimetre Arrays)

background limited sensitivity for a photon counting detector
BACKGROUND-LIMITED SENSITIVITY FOR A PHOTON COUNTING DETECTOR

S = Signal DS = Uncertainty in signalNS = Signal photon rate (photons/second/Hz) NB = Background photon rateDn = Bandwidth of radiation frequencies acceptedt = Exposure (integration) time

how to get good sensitivity

Use a big telescope

Accept a wide band of frequencies

Collect photons for a long time

Reduce unwanted background radiation:e.g:• Cool the instrument and/or telescope• Get above the Earth’s atmosphere

HOW TO GET GOOD SENSITIVITY:
a modern cryogenic focal plane planck hfi instrument

JFET box at 50 K(JFETs at 100 K)

Back-to-back horns at 4 K

Filters at 1.6 K

Bolometers, horns and filters at 0.1 K

Mounting flange (20 K)

A modern cryogenic focal plane: Planck HFI instrument.
cryogenic system for far infrared instrument

STORAGE TANKS

FLOW CONTROL

4He

CRYO-COOLER

4-K COLD TIP

3He

GAS EXHAUST

TO SPACE

4-K SHIELD

2-K HEAT

EXCHANGER

2-K SHIELD

HEAT EXCHANGER

GAS EXPANSION

PRODUCING 2-K

3He - 4He

MIXING

0.1 K STAGE

Cryogenic system for far-infrared instrument.
slide25
Very high sensitivity bolometric detector:- operating at 100mK (so-called Spider-web detector)- Ge:Ga NTD thermometer.

Sensitivity:

1x10-17 W/Hz1/2

the effects of atmospheric turbulence

Atmosphere

THE EFFECTS OF ATMOSPHERIC TURBULENCE

 = 550 nm Theoretical Achieved Resolution Resolution ("seeing")

Palomar 5-m: 0.03" ~ 1”Keck 10-m: 0.015" ~ 1"

HST 2.4-m: 0.06" ~0.06"

Plane wavefront at top of atmosphere

Distorted (corrugated) wavefront at the ground

Distortion varies: Timescale of ~ 10 ms (coherence time) Length scale of ~ 30 cm (coherence length)

wavefront distortions
WAVEFRONT DISTORTIONS

1st order distortion (wavefront tilt):

Image “dances around” in the focal plane

2nd order distortion (wavefront curvature):

Image comes in and out of focus

the eagle nebula

Hubble Space Telescope0.6 m

SCUBA on the JCMT850 m

Infrared Space Observatory 7 m

THE EAGLE NEBULA
cobe satellite 1989
COBE SATELLITE (1989)

FIRASFar Infrared Absolute Spectrometer

Measured CBR spectrum

DMRDifferential Microwave Radiometer

Measured spatial fluctuations in CBR temperature

cobe firas
COBE FIRAS

TCBR = 2.73 K

small variations in t cbr detected by cobe dmr

0.1%

Photon frequency increased  Hotter

100%

Photon frequency decreased  Colder

SMALL VARIATIONS IN TCBR DETECTED BY COBE DMR

Variation of 3 mK

slide37

Our galaxy

Hot gas in clusters of galaxies

FOREGROUNDS MUST BE SUBTRACTED

Instrument noise

Other galaxies

The real signal

slide38

 (mm)

 (cm)

Free-free

Synchrotron

q = 30 arcmin.

(T/T)rms

Dust

Trms (K)

q = 10 arcmin.

(T/T)rms

n (GHz)

n (GHz)

FOREGROUND FLUCTUATION LEVELS

EXTRAGALACTIC POINT SOURCES

GALACTIC (HIGH LATITUDE)

Best frequency for cosmological signal ~ 150 GHz

how the cbr power spectrum should evolve

PRIMORDIAL FLUCTUATION SPECTRUM

T

T

Large angularscales

1/(Angular scale)

Small angularscales

EVOLUTION

T

T

TODAY

1/(Angular scale)

Small angularscales

Large angularscales

HOW THE CBR POWER SPECTRUM SHOULD EVOLVE

angular power spectrum of cbr variations inflationary cdm model with o 1

Angular scales probed by COBE

T

T

Depends on  ,  B, H, etc.

Primordial

ANGULAR POWER SPECTRUM OF CBR VARIATIONS (INFLATIONARY CDM MODEL with o = 1)

Angle (degrees)

0.1

10

1

Large angles (1/Angular scale) Small angles

how to measure the cbr variations very well
HOW TO MEASURE THE CBR VARIATIONS VERY WELL

1. Measure to one part in 1,000,000 Use a cold telescopeand put it as far away from the Earth as possible

2. Cover a large amount of sky

3. Observe in the 1 - 2 mm wavelength region

4. Use a big telescope to see fine details (resolution of ~ 0.1o = 6 arcminutes)

5. Look through the fog . . .

planck orbit and sky mapping strategy
PLANCK ORBIT AND SKY MAPPING STRATEGY

Planck at L2

Earth

1.5 million kmfrom Earth

Sun

simulated cobe sky map cdm model 1 beam 7 o t t 2 x 10 5
SIMULATED COBE SKY MAPCDM MODEL = 1 Beam = 7 oT/T = 2 x 10-5

SIMULATED PLANCK SKY MAPCDM MODEL = 1 Beam = 1/6 oT/T = 2 x 10-6

cbr anisotropies after map and planck

MAP

Planck

CBR ANISOTROPIES AFTER MAP AND PLANCK

• H, , B,  will be measured to an accuracy of a few %

• The inflation theory will be tested

• The origin of cosmic structure will be known

accuracy of retrieval of fundamental parameters from planck cbr anisotropy maps
ACCURACY OF RETRIEVAL OF FUNDAMENTAL PARAMETERS FROM PLANCK CBR ANISOTROPY MAPS

 b

H

 o

1- uncertainty (%)

1/3 sky coverageT/T = 2 x 10-6 per pixel

Angular resolution (degrees)

slide49

The Atacama Large Millimetre Array (ALMA)

Multi-element interferometer with ~ 60 12-m

antennas

Mountain-top site in Chile (alt. 5000 m)

Variable configuration (100 m – 10 km)

Angular resolution ~ 20 milli-arcseconds

Operating ~ 2008

far infrared space telescope first
Far Infrared Space Telescope (FIRST)

3.5-metre telescope, cooled to ~ 80 K

Sunshield with solar panels on other side

Star-trackers for pointing

2500-litre tank of liquid helium cools instruments inside to 2 K

Warm electronics and thrusters

Wavelength range50 - 700 m

Major scientific projects:- Study of distant galaxies- Star formation - Interstellar chemistry

the next generation space telescope ngst

THE NEXT GENERATION SPACE TELESCOPE (NGST)

  • 8-m diameter deployable telescope cooled to 30 K
  • Wavelength range 0.5 – 30 m
  • 10-year lifetime
  • Far-earth orbit (1-3 AU from Earth)
  • Launch ~ 2010
  • Main scientific goals: - Galaxies in the early universe - Large-scale structure - Planetary system formation - Chemical evolution of the universe
conclusions
CONCLUSIONS

Space observations of the CBR will either

Prove that currently trendy ideas in cosmology and

high energy physics are valid and quantify all of the

main cosmological parametersor

show that new ideas are needed

  Cosmologists will have to find other questions to argue about