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The SZE in groups of galaxies
Why? How? Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Normal groups (overdensity ≈ 200)
Groups of galaxies half of galaxies are in groups laboratory for environmental effects transition from clusters to single galaxies building blocks of clusters Normal groups (overdensity ≈ 200) massive clusters rare at high z! Compact groups (overdensity ≈ 105) densest galaxy densities in Universe laboratory for extreme environmental effects are many CGs = chance alignments of galaxies? within normal groups, clusters, filaments heavy contamination by projection effects? Hernquist et al. 95 Walke & Mamon 89 Mamon 86 Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Science with SZ in Groups
Quantify alignment along line of sight Internal structure Evolution of group gas properties but can’t measure T at medium to high z! Better stats on n(z) to constrain cosmology Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Can X-rays settle the alignment debate?
X-ray emission traces gravitational potential intergalactic gas in hydrostatic equilibrium with group potential X-rays less subject to projections ROSAT, ASCA 30-80% of CGs have diffuse X-ray emission Mulchaey et al. 96; Ponman et al. 96 Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Compact groups in X rays
HCG 62 Vrtilek et al. 00 HCG 16 Mamon et al. unpub Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Luminosity - Temperature relation
Osmond & Ponman 04 groups clusters Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Do X-rays measure gas mass?
Unresolved groups If V ≈ a2 c gas mass / alignment degeneracy Ostriker et al. 95 can be lifted by SZ measurements } Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Groups vs Rich Clusters
1013 Msun 1015 Msun 1000 x lower 300 x lower Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Observability: 1) sensitivity
1013 Msun ygroups ≈ 5 x 10-7 3 detection at South Polar Telescope in 40 hr! better with ALMA if we smooth y maps? 1 detection at South Polar Telescope in 4.5 hr stack groups Planck/1yr 3 x 1013 Msun Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Observability: 2) angular size
1013 Msun M*(z) = M ALMA will resolve groups at all redshifts but not detect them unless one smoothes the map? SPT will barely resolve groups at all redshifts Gary MAMON, ALMA-SZ workshop, 8 April 2005
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Conclusion Relative to clusters, groups are more visible in SZ than in X-rays But, because of lack of sensitivity of SZ instruments (relative to X-ray instruments), groups are extremely hard to detect, even with ALMA or SPT Gary MAMON, ALMA-SZ workshop, 8 April 2005
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