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Baryon content of galaxy groups. Ming Sun (University of Virginia) . M. Voit, M. Donahue ( MSU ) A. Vikhlinin, W . Forman, C . Jones ( CfA ) N. Sehgal ( KIPAC ) C . Sarazin ( Virginia ). group. Groups? Why do we care ?. cluster. cluster. group. Mass function. 10 15 M ʘ. - PowerPoint PPT Presentation
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Baryon content of galaxy groups
Ming Sun (University of Virginia)
M. Voit, M. Donahue (MSU) A. Vikhlinin, W. Forman, C. Jones (CfA) N. Sehgal (KIPAC) C. Sarazin (Virginia)
Groups? Why do we care?
1015 Mʘ 1013 Mʘ
groupcluster
Galaxy groups are the smallest halos where the bulk of baryons are accounted for .
Mass function
groupcluster
Detected baryons(McGaugh + 2010)
Groups are :
1) Ideal systems to study baryonic physics (e.g., SN winds, cooling, AGN heating), which dominates the systematic uncertainties for cluster cosmology.
2) The same baryonic physics is important to understand the formation and evolution of galaxies (most galaxies are in groups).
Stellar fraction(McGaugh + 2010)
Are groups gas / baryon poor ?
Are groups metal poor ?
Sun + 2009 ; Vikhlinin + 2009, Chandra samples (r2500 ~ 1/3 rvir , r500 ~ 2/3 rvir)
Groups are gas poor around the center
cosmic baryon fraction cosmic baryon fraction
LX - T
Groups(Sun+09), Chandra
+
REXCESS(Pratt+09, +10), XMM
(both samples also agree well on other scaling relations)
Bolometric< r500
Bolometric(0.15 r500, r500)
2.91
2.85
Are groups gas poor at large radii ?
Vikhlinin + 09; REXCESS (Pratt + 09); Sun + 09
Humphrey et al. 2011, Chandra
Deep observations are required for gas at large radii !
LX, 2500 / LX, 500 ~ 4/5vs.
Mgas, 2500 / Mgas, 500 ~ 1/4
1012 1013 1014 1015
M2500 or M500 (Mʘ)
Pressure content in groups
Sun, Sehgal + 2011
The key to understand the SZ power spectrum (from SPT and ACT) as ~ half of the SZ power at l = 3000 comes from low-mass systems !
Low SZ power measured from SPT ( ~50% of expected for 8 = 0.8)Lueker + 2010 and Shirokoff + 2011
What about baryon content in groups?
1) fgas at r > r500 (NFW, β=0.5, ~ 80% increase from r500 to r101 ) (but, slope change? mass bias? sample bias? clumping?) 2) Intragroup light (IGL) ?
cosmic baryon fractioncosmic baryon fraction
(Lin+03; Gonzalez+07; Giodini+09 Sun+09; Vikhlinin+09)
stars gas + stars
Are groups gas / baryon poor ?
Are groups metal poor ?
Baumgartner et al. 2005
Are groups metal (iron) poor ?
Emission-weighted (ASCA) Mgas-weighted
Sun et al. 2011
(also see Rasmussen & Ponman, 2009; Bregman + 2010)
Why ? metal loss at early time (e.g., SN winds, Quasars) late time (e.g., radio AGN)
Group gas is also iron poor around the center
If all metals produced were kept …
abundance ofclusters
Looking forward …
1) Hydrostatic equilibrium mass to be calibrated2) Selection bias ? --- (try different samples)3) Extending to lower masses ! (low nH and back.)4) Go beyond r500 (e.g., stacking)5) More theory / simulation work
Conclusions:
1) Groups are gas poor around the center (e.g., < 1/3 rvir) but not necessarily gas poor at large radii. The gas distribution has important implications on e.g., feedback and SZ power spectrum.
2) Groups have a higher SF efficiency than clusters but the group stellar fraction (including IGL) needs to be better constrained.
3) Groups are also metal (iron) poor around the center (e.g., < 1/3 rvir) .
The End
Entropy scaling relations
(Sun et al. 2009, 43 groups; Vikhlinin et al. 2009, 14 clu.; Pratt et al. 2010, 31 clu.)
Halo mass
Ste
llar m
ass /
Hal
o m
ass
Halo Stellar Fraction
Sehgal et al. 2010
Arnaud et al. 2010(REXCESS)
Battaglia et al. 2010
Shaw et al. 2010
Trac et al. 2010
Sun, Sehgal et al. 2011
Why are groups metal poor?
Systematic issues:1) “iron bias” (Buote 2000) for group cool cores, but NOT the reason here2) “inverse iron bias” (Rasia et al. 2008) for 2 – 3 keV systems, up to 40%
Physical reasons:1) re-accretion of pristine gas (e.g., Renzini 1997) ?2) metal loss at early times (SN winds)? related to pre-heating (see Rasmussen & Ponman 2009)3) late-stage metal loss (AGN? Kirkpatrick et al.; Simionescu, Werner et al.)
1) No pretty Chandra images
2) Hydrostatic equilibrium mass
3) Selection bias
4) Correlated errors
Are groups gas poor at large radii ?
Vikhlinin + 09; REXCESS (Pratt + 09); Sun + 09
@ r500
LX - T
Groups(Sun+09), Chandra
+
REXCESS(Pratt+09, +10), XMM
Bolometric< r500
0.5-2 keV< r500
Bolometric(0.15 r500, r500)
0.5-2 keV(0.15 r500, r500)
2.91
2.85
2.60
2.55