1. Array for Microwave Background Anisotropy AMiBA SZ Science AMiBA Team NTU Physics Figure 4. Simulated AMiBA deep surveys of a 1deg 2 field (no primary CMB added) with 340hrs integration. A maximum likelihood method was used to reconstruct the images from a set of simulated visibility data. Pixel values are in units of Jy/beam. (Left) 12+1 heterogenous array (A): 169 hexagonally packed mosaic, thermal noise sensitivity of 0.55 mJy/beam. (Right) 19-elements array (B) - 91 hexagonally packed mosaic, thermal nlise sensitivity of 0.45mJy/beam Input SZ signal map (no primary CMB) 2. Science Planning – Dish Configuration for SZ Science Example of SZ signal from cosmic structures Example of CMB+SZ sky map at 94GHz (sign flipped) Realization of random Gaussian primary CMB sky + = Maximally close packed 7 dishes of 1.2m Primary CMB rms contribution D=60cm D=120cm ASIAA 1. Introduction sigma8=0.94 preheating T-SZE @ 94GHz dT sz / 2.73K = -1.56y @ 94GHz Hexagonal configuration with 20cm gaps, equivalent to a cut-off multiple of l=400 Comparison of simulated SZ+CMB AMiBA sky (1deg 2 ) Hole distribution available on the 6m AMiBA platform In detecting weak SZ signals from galaxy clusters, the primary CMB acts as a scale-dependent noise source dominant on large scales (see Fig.1) that will limit the achievable sensitivity in surveys. Hence, it is crucial for the project to make a secure design of the dish configuration for the AMiBA science. Based on extensive simulations we concluded that the hexagonal configuration of seven 1.2m dishes using the 1.4m separation hole pattern is the most optimal for SZ cluster science among available configurations – the maximally close-packed configuration using the 1.2m hole pattern will suffer from a severe dilution of the SZ signal by the large-scale primary CMB. Figure 1. Model power spectra of the primary CMB and the secondary (thermal) Sunyaev-Zel’dovich effect at 94GHz. Figure 2. (Top) Example of the simulated CMB + SZ sky signal on a 1deg 2 FoV. In SZ observations the primary CMB acts as a scale-dependent noise source dominant on large scales, l<2,500. (Bottom) Comparison of simulated SZ+CMB AMiBA fields between the two hexagonal dish configurations of our concern (left: using the 1.2m hole pattern, right: using the 1.4m hole pattern). No system noise added. It is clearly demonstrated that under the maximally close-packed configuration (left) AMiBA is very sensitive to the primary CMB signal on large scales, which will highly dilute the SZ signal. With 20cm gaps between adjacent dishes, AMiBA will perfectly filter out the primary CMB below l=400. Table 1. Mean rms contribution using 6 realizations of 1deg 2 CMB maps. Using the 1.4m hole pattern (20cm gaps) the primary CMB contribution can be reduced down to 0.9mJy/beam, which is well below typical of system noise sensitivities. 3. Science Planning – Alternative expansion to the full 19 dishes 19-element full expansion – maximum sensitivity, best- achievable uv-coverage Expensive, Slow, Severer gravitational platform deformation, primary CMB dilution Question: Alternative expansions to increase both the sensitivity (photon collecting area and uv-coverage) and speed (less additional Rx/electronics)? (C) Figure 3. Possible dish configurations for the future AMiBA expansion: (A) mixed twelve 1.2m + one 2.4m dishes, (B) full expansion to 19 dishes of 1.2m, (C) close-packed 13 dishes of 1.2m using the 1.4m hole pattern, (D) 13 dishes of 1.2m covering the same uv-coverage as (A). 4. Expected performance of AMiBA SZ surveys To make sky maps with realistic SZ signals we use results from pre-heating cosmological simulations of an LCDM model (Ω m =0.34, Ω λ =0.66, Ω b =0.044, h=0.7, σ 8 =0.94) in a 100Mpch -1 comoving box which reproduces the observed cluster Mx-Tx and Lx-Tx relations at z=0 (K.Y. Lin et al. 2004, ApJ, 608, L1). As an AMiBA specification we adopt a close-packed hexagonal configuration of 19 * 1.2m dishes co-mounted on a 6m platform. This yields a synthesized beam of FWHM=2 arcmin (600kpc/h at z=0.8) which is optimized to detect high-z clusters. The FoV of the primary beam is about 11 arcmin. To generate mock visibility data we performed a mosaic survey of 9 x 9 pointings covering ~ 1deg 2 integrating 420hrs/deg 2 (T sys =80K, 16GHz bandwidth). Figure 6 shows a predicted redshift distribution (solid) of clusters in a mock AMiBA deep survey in comparison with the input model (dotted). Figure 7 shows cluster number counts as a function of peak flux threshold derived from 17deg 2 sky maps. The false detection rate is reduced down to 10% at the peak flux threshold of 3.3mJy/beam (Umetsu et al. 2004, MPLA, 19, 933). One of the main science goals of AMiBA is to conduct blind galaxy-cluster surveys via the thermal Sunyaev-Zel’dovich (SZ) effect to search for high-z clusters. Measurements of cluster masses and number density as a function of redshift can be used to constrain the cosmic matter density, and, for sufficiently large cluster samples, the amount and nature of dark energy as well as the normalization parameter  8 of the matter power spectrum. We present our recent efforts on the science planning for the AMIBA SZ experiment based on simulations, in particular (1) dish configuration for SZ observations and (2) alternative expansions to the full 19-elements. Figure 6. Redshift distribution of clusters selected from a simulated 17deg 2 AMiBA deep survey with the full 19 elements of 1.2m dishes (red). The limiting flux is 3.3mJy per 2 arcmin beam. Also plotted is the noise- free input model (black) from preheating cosmological N-body simulations. N ~ 5 halos/deg 2 @10% false rate N ~10 halos/deg 2 @ 20% false rate - -> dN/dt ~ 70 clusters/year Figure 6. Cumulative distribution functions of cluster number counts as a function of peak SZ flux threshold (mJy/beam): input model (red), simulated AMiBA total detections (blue), and AMiBA real detections (green). Conclusions for the AMiBA Dish Configuration Close-pack will see lots of low-l primary CMB signals that will contaminate the weak SZ signals from clusters and will limit the achievable sensitivity in a survey. The 1.4m hole pattern is optimal among our available hole patterns in the sense that (1) it will capture bulk of the cluster signal (2) it will filter out the primary CMB below l=400. Based on the simulations AMiBA has decided to use this 1.4m separation hole pattern. Sensitivity Comparison Sept. 20062008?2009? ? Figure 5. AMiBA expansion plan. Hexagonal pattern using 1.4m separation holes to filter out the primary CMB (see Section 2) Implications: In terms of the image quality and the sensitivity, the full 19-element array works better than the 12+1 heterogeneous array – 1.4 times in terms of the survey speed. However, the close-packed 19-element array will suffer from a severe dilution of the weak SZ signal by the primary CMB at large scales. References: K. Umetsu et al. 2004, MPLA, 19, 1027 K. Umetsu et al. 2005, astro-ph/0506065 K. Umetsu, 2005, “Heterogeneous array”, AMiBA Report (http://amiba.asiaa.sinica.edu.tw/Documentation/AMiBAreports.html)http://amiba.asiaa.sinica.edu.tw/Documentation/AMiBAreports.html K. Umetsu, 2006, “Dish Configuration”, AMiBA Report (http://amiba.asiaa.sinica.edu.tw/Documentation/AMiBAreports.html)http://amiba.asiaa.sinica.edu.tw/Documentation/AMiBAreports.html