the sunyaev-zel’dovich effect ami day, 2011 september 30

The Sunyaev-Zel’dovich effect

The Sunyaev-Zel’dovich effectAMI day, 2011 September 30

Mark Birkinshaw

University of Bristol

2011 September 30 Mark Birkinshaw, U. Bristol 2


The thermal SZ effect

The effect comes from the inverse-Compton scattering of the CMB by the hotter electrons in the ICM.

Thermal SZ effect strength Comptonization parameter, ye, the dimensionless electron temperature weighted by the scattering optical depth.




Total SZ flux density

thermaleeRJ UdzTndS • z-independent measure of ICM thermal energy content• Virial theorem – measures gravitational potential energy unless cluster in dynamically-active state

• With X-ray data for electron temperature, get gas mass and lepton count, hence baryonic mass fraction



Now easy to detect for known clusters such as those from X-ray surveys

e.g., Lancaster et al. (2011) complete sample of 18 high-LX ROSAT BCS clusters (Ebeling et al. 1998) at z > 0.2

• OCRA-p on Toruń 32-m (OCRA-F now being debugged; OCRA-C possible)

• noise ~ 0.4 mJy [less than 1 hour/cluster]AMI highly effective at this (e.g.,

Rodríguez-Gonzálvez et al. 2011, Shimwell et al. 2011)




Harder work in blank fields, but rewarding because of expected linear scaling with Uthermal; e.g.,

• Planck survey (Planck collaboration 2011), 189 clusters to z = over 3 104 deg2 (ERSC)

• ACT survey (Marriage et al. 2010), 23 clusters to z = 1.07 over 455 deg2 (2008 dataset)

• SPT survey (Vanderlinde et al. 2010; Williamson et al. 2011), 21 clusters to z =1.16 over 178 deg2 (2008 dataset), 26 high-significance clusters to z = 1.13 over 2500 deg2 (2010 dataset)




Cluster numbers appearing in surveys are lower than original estimates 8 assumptions– optimistic assumptions about survey performance– confusion levels on primordial CMB and source

populations

• Value of survey high – want to get to lower cluster masses (currently see only mass function above 3 1014 M)




Source contaminationSZ effects usually evident before source correction – compare cluster and trail statistics.

Uncorrected: lose 20% of clusters.Corrected: lose 10% of clusters (5% of trails).Lancaster et al. (2011)



Source contaminationContamination also important in sub-mm: e.g., Bullet cluster (Johansson et al. 2011) – lensed sub-mm galaxies dominate image

Need multi-resolution (AMI-type interferometer) and/or multi-frequency data.



Scaling relation: flux density/X-ray kT

Low-z scaling relations consistent with expected self-similar model, but errors large – LX and TX ranges too small (Lancaster et al. 2011)



Next step: blind survey

Potential field: XMM-LSS. Survey blind in SZ, provides parallel X-ray, lensing, IR data.

Too far south for Toruń: accessible to AMiBA.



Train-wreck astronomy

RXJ 1347-1145 (z = 0.45) GBT/MUSTANG, 90 GHz, 10 arcsec resolution (Mason et al. 2010)Left: colour = SZ; green = HST/ACS; contours = surface mass density (Bradac et al. 2008). Right: contours= SZ; colour = X-ray (Chandra)




MACS 0744+3927 (z = 0.69): shock discovered with high resolution SZ observations: GBT/MUSTANG, X-ray; Korngut et al. (2010)




MACS J0717.5+3745

z = 0.548

Clearly disturbed, shock-like substructure, filament

What will the SZ image look like?




MACS J0717.5+3745, z = 0.548, AMI image



Science to come• Cluster physics

– Now getting fast SZ follow-up of known clusters to very high redshift (AMI, OCRA, etc., etc.)

– SZ gives linear measures of energy and mass – excellent probes of structure formation from appropriate samples, and testing scaling relations

– Resolving train-wreck structures – measures of thermalization of kinetic energy and cluster formation

• Cosmology– Structure formation and cosmological parameters from cluster counts:

need to go factor 5 – 10 below current mass limits– Baryonic mass fraction measurements with redshift and radius (lensing)

• Other SZ observables (kinematic effect, spectral distortions, polarization)

the sunyaev-zel’dovich effect ami day, 2011 september 30

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