1. The SZE in groups of galaxies
Why?
How?
Gary MAMON, ALMA-SZ workshop, 8 April 2005

2. 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

3. 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

4. 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

5. 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

6. Luminosity - Temperature relation
Osmond & Ponman 04
groups
clusters
Gary MAMON, ALMA-SZ workshop, 8 April 2005

7. 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

8. Groups vs Rich Clusters
1013 Msun
1015 Msun
1000 x lower
300 x lower
Gary MAMON, ALMA-SZ workshop, 8 April 2005

9. 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

10. 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

11. 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