The Sunyaev-Zel’dovich Effect

Jason GlennAPS

Historical PerspectivePhysics of the SZ Effect--------------------------------------------Previous Observations & ResultsBolocamImminent ExperimentsFuture WorkReferences

Historical Perspective•CMB discovered in 1964 by Penzias and Wilson•COBE 1989: perfect blackbody to 1/105, primary anisotropies measured•However, in 1970 Sunyaev & Zel’dovich predicted the SZ effect: secondary anisotropies in the CMB

TCMB = 2.725 K

Physics of the SZ EffectMechanism & Thermal Effect

last scatteringsurfacez ~ 1100

CMB photonsT = (1 + z) 2.725K

galaxy cluster with hot ICMz ~ 0 - 3

scatteredphotons(hotter)

observerz = 0

Sunyaev & Zeldovich (1970)

Spectralshift

CMB photons have a ~1% chance of inverse Compton scattering off of the ICM electrons; photon number is conserved

Physics of the SZ EffectFunctional Form

•Temperature shift proportional to the gas pressure, neTe, & mass dl•CMB photon energies boosted by ~kTe/(mec2)•kTe ~ 10 keV, Te ~ 108 K relativistic •x = h/(kTe)

•f(x) is the spectral dependence •Notice that the temperature shift is redshift independent unbiased surveys for clusters

y parameter

Physics of the SZ EffectThe Kinetic Effect: a Doppler boost from the peculiar velocity of the cluster

Spectral distortion:

Kinetic effect is small

Null in thermal measure kinetic

Increment

Decrement

Physics of the SZ EffectWhat the thermal effect looks like

•Simulations, of course! = 2 mm•“Maps” are 1° on a side•SZ effect is an increment at 2 mm

Physics of the SZ EffectThe Angular Power Spectrum

•Secondary anisotropies can be measured independent of cluster detection•l is the multipole number (as in quantum mechanics); (°) ~ 200°/l•Vertical units: T2 – power usually measured as an excess variance above the noise, Cl is per l – there are more independent multipoles at high l•Dashed and dotted lines are models•The signals are small: ~ 15 mK @ 30 GHz, ~ 5 mK @ 150 GHz•Tentative detections so far (more on this Friday)

Green is 30 GHz, or 1 cmPink is 150 GHz, or 2 mm

Physics of the SZ EffectCosmological Utility

What can be measured when combined with other observations:•H0•Cluster masses•Cluster abundance as a function of redshift, , w•Spectral index of initial perturbations (non-Gaussianity)•Cluster evolution

Next, we’ll discuss SZ observations and some results

Previous ObservationsImages from Interferometers

•Image from Carlstrom group using OVRO/BIMA interferometer at 30 GHz•Spectral measurements a compendium – confirms spectrum through RJ tail•To date, only pointed observations toward massive clusters•Measurements of the kinetic effect will be very hard, depending on precision of multiband calibration

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHz

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHzContamination by cluster, foreground, and background radio point sources (quasars) would be a problem at 30 GHz.

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHzContamination by cluster, foreground, and background radio point sources (quasars) would be a problem at 30 GHz.Contamination by dust from background, lensed galaxies is a potential problem at 1 mm.

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHzContamination by cluster, foreground, and background radio point sources (quasars) would be a problem at 30 GHz.Contamination by dust from background, lensed galaxies is a potential problem at 1 mm.In practice, the angular resolution achievable with each is about the same because bolometer arrays are used for short-wavelength observations and interferometers are used for long-wavelength observations.

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHzContamination by cluster, foreground, and background radio point sources (quasars) would be a problem at 30 GHz.Contamination by dust from background, lensed galaxies is a potential problem at 1 mm.In practice, the angular resolution achievable with each is about the same because bolometer arrays are used for short-wavelength observations and interferometers are used for long-wavelength observations.1 mm and 2 mm observations are necessary to measure the kinetic SZ effect.

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHzContamination by cluster, foreground, and background radio point sources (quasars) would be a problem at 30 GHz.Contamination by dust from background, lensed galaxies is a potential problem at 1 mm.In practice, the angular resolution achievable with each is about the same because bolometer arrays are used for short-wavelength observations and interferometers are used for long-wavelength observations.1 mm and 2 mm observations are necessary to measure the kinetic SZ effect.Emission/absorption by the atmosphere is not a huge problem at long wavelengths for interferometers because the noise between telescopes is not highly correlated.

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

The amplitude of the SZ thermal effect is larger at 30 GHzContamination by cluster, foreground, and background radio point sources (quasars) would be a problem at 30 GHz.Contamination by dust from background, lensed galaxies is a potential problem at 1 mm.In practice, the angular resolution achievable with each is about the same because bolometer arrays are used for short-wavelength observations and interferometers are used for long-wavelength observations.1 mm and 2 mm observations are necessary to measure the kinetic SZ effect.Emission/absorption by the atmosphere is not a huge problem at long wavelengths for interferometers because the noise between telescopes is not highly correlated. In contrast, atmospheric noise is much worse at short wavelengths – much worse than anticipated!

Some Questions•What are the tradeoffs between 30 GHz (1 cm) and 150/270 GHz (2mm/1mm) observations?

Clearly, we need both.

Atmospheric NoiseEmission, rather than absorption, is the primary problem: fluctuation in the arrival rate of background photons from water molecules in the sky (and the telescope, the ground, the instrument…)

The sky over Mauna Kea

Emission = 1 - Transmission

300 m

1 mm2 mmcm band

Bolocam

Physics of the SZ EffectThe Angular Power Spectrum

Green is 30 GHz, or 1 cmPink is 150 GHz, or 2 mm

We need more high-l data!

Si3N4 micromesh “spider web” bolometerJPL Micro Devices Lab

Absorber

Weak ThermalLink

Bath (T ≤ 270 mK)

Q

Incoming Photons

BolocamDetectors

Oh, Langley devised a bolometer:It’s really a kind of thermometerWhich measures the heatFrom a polar bear’s feetAt a distance of half a kilometer1. 1Anonymous

In 1878, Samuel Pierpont Langley invented the bolometer.

BolocamBolometers

Oh, Langley devised a bolometer:It’s really a kind of thermometerWhich measures the heatFrom a polar bear’s feetAt a distance of half a kilometer1. 1Anonymous

In 1878, Samuel Pierpont Langley invented the bolometer.

With Bolocam on the CSO, we can detect a polar bear’s foot with a S/N of one at a distance of 3 km in one second of integration time2.

2(In good weather!)

BolocamBolometers

Focal Plane Bolometer Array

5 in.

•144 bolometers = 1.1, 2.1 mm•300 mK

CSO

CUCaltechJPLCardiff

Cryostat

Collaborators (Cardiff, Caltech, JPL, & CU)P.A.R. Ade, J.E. Aguirre, J.J. Bock, S.F. Edgington, A. Goldin, S.R. Golwala, D. Haig, A.E. Lange, G.T. Laurent, P.R. Maloney, P.D. Mauskopf, P. Rossinot, J. Sayers, P. Stover, H. Nguyen

BolocamInstrument

Thanks to Sunil for some graphics in this lecture!

BolocamThe reality of sky noise (a must read for theorists)

“Average” subtraction takes out 90% of the noise, but we need >99% with retention of large-scale structure

Bolocam is a bolometer-array pioneer and the other groups are looking to us; we’re only in the lead by ~12 months! (this part is for you, Andrew)

“White” noise: ultimate sky subtraction

Residual noise and itsy-bitsy SZ signal!

Imminent MM-Wave ExperimentsHigh-l Anisotropies

Nils

ReferencesAn excellent review from an observer’s perspective and the source of some of the graphics in this lecture: “Cosmology with the Sunyaev-Zel’dovich Effect”, Carlstrom, Holder, & Reese, ARAA, 2002, Vol. 40, pp. 643-680

•H0:

•Cluster mass fraction:

•Cluster peculiar velocities:

Long-Term Future WorkProbing the physics of galaxy cluster evolution

Hallman & Burns, et al.