The Sunyaev-Zel’dovich effect is of particular importance in the study of high-redshift galaxy clusters due to its redshift independence, not taking into account the galaxy clus- ter angular diameter distance cosmic evolution. The examination of structure in galaxy clusters across a wide redshift range can also give important insight into the degree of disturbance in the ICM at different cosmic epochs.
In addition, having established that a wide redshift- and mass-range study is vital for galaxy cluster studies if one is to constrain the cosmological parameters to high accuracy, particularly with regard to the dark energy equation of state parameter and its evolution, it now remains to discuss the redshift range that current and future instruments can probe.
The Planck survey has detected galaxy clusters out to redshiftz= 0.99 (Planck Col- laboration XX 2013). In addition, the highest redshift clusters yet detected by the SPT and ACT surveys are at z= 1.32 (Stalder et al. 2013) andz= 1.36±0.06 (Hasselfield et al. 2013) respectively.
Mass-limited surveys, however, do not have the required sensitivity to detect clusters at very high redshift with low mass over a large survey volume. The IRAC Distant Cluster Survey (IDCS) identifies clusters via photometric studies, the redshifts being spectroscopi- cally confirmed via follow-up studies. One such example is the cluster IDCS J1444.2+3306 at *zspec= 1.89+ (Zeimann et al. 2012).
In addition, Brodwin et al. (2012) followed up an IDCS detected cluster atz = 1.75 with 31 GHz SZA. This is one of the most distant cluster with a mass of M200 = (4.3±1.1)×1014M# observed via SZ up till now. The XMM-Newton Distant Cluster project (XDCP) (de Hoon et al. 2013) discovered az= 1.45 cluster whose surface bright- ness profile was fit with a beta model. Spectroscopic fitting in annular bins was however not feasible due to the low photon count statistics. Gobat et al. (2011) have reported the
3.4. Redshift range of detected galaxy clusters 39 existence of a mature cluster at redshift z = 2.07, first discovered via a galaxy overden- sity in Sptizer data and then confimed by 3.5σ XMM-Newton observations of the galaxy cluster’s extended ICM emission within 20$$−30$$.
Selected future instruments
CCAT will be a 25 m telescope, to be completed by 2016, operating over a frequency range of 200−2200àm. It will probe the ICM via Sunyaev-Zel’dovich observations out to high z ∼1−2 redshifts (CCAT Cosmology Report 2013). It is the combination of wide frequency coverage and high sensitivity alongside with simultaneous multi-colour obser- vations which will make it one of the most promising instruments in the next few years.
In addition, its complementarity with high-resolution ALMA observations highlights the need for the development of tools for interferometer/sd combination techniques.
eRosita will start observing at the beginning of 2016 and will perform an all-sky sur- vey detecting galaxy clusters with a median redshift of z = 0.35 (Pillepich et al. 2012).
The planned X-ray Athena+ mission will enable a selection of the eRosita/Euclid/LSST clusters to be followed up at high spatial and spectral resolution out to redshifts around z= 2 (Pointecouteau et al. 2013).
The LSST will be a ground-based telescope that will cover six bands, allowing weak lensing studies to be made with a median redshift of 1.2 for observing set-ups that will give 56 galaxies per arcminute squared (Ivezic et al. 2008).
The Euclid satellite, to be launched in 2019, contains a 1.2m dish with which one will be able to study the clustering of galaxies and make weak lensing estimates over a wide redshift range (Euclid report 2011). It will cover 15 000 deg2 in the wide survey, which will then be followed up with two deep field surveys a 20 deg2.
The recently lauched NuSTAR satellite will enable the temperature in galaxy cluster shock fronts to be measured more accurately than Chandra. The latter suffers from its lack of ability in measuring high temperatures in soft bandpasses such that NuSTAR greatly enhances our current understanding of the very hot gas in galaxy clusters.
Future SZ targeted observations from Mustang 1.5 and MUSIC in conjunction with cur- rently operating bolometer ACT, SPT and Bolocam instruments will further enhance our knowledge of the ICM in galaxy custers. Interferometric data from AMI, CARMA/SZA and ALMA/ACA will significantly complement this picture (Chapter 7).
Figure 3.12: Current and future instruments that have or are expected to have a sig- nificant impact on galaxy cluster studies. [Image credits: (SPT (KICP Chicago), Planck (ESA), ACT telescope (ACT), CCAT (Caltech: CCAT website), e-ROSITA (Merloni et al. 2012), LSST (LSST Collaboration), Spitzer (NASA/JPL), Euclid (ESA - C. Carreau), ALMA/ACA artist’s impression (ESO/NAOJ/NRAO), CARMA/SZA (CARMA website), AMI (Astrophysics Group Cambridge website), Athena+ (Ettori et al. Athena+ support- ing paper (The Astrophysics of galaxy groups and clusters)), Bolocam (Caltech: BOLO- CAM website), APEX-SZ (APEX-SZ collaboration), MUSTANG 1.5 (NRAO website), GISMO (IRAM 30m, credit IRAM), Chandra (NASA/CXC/NGST/M.Weiss), XMM- Newton (ESA, D.Ducros), NuSTAR (NuSTAR), Hubble (NASA)]