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 ID: 541809
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Slide1
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)Slide2
Groups? Why do we care?
10
15 Mʘ
10
13
M
ʘ
group
cluster
Galaxy groups are the smallest halos where the bulk of baryons are accounted for .
Mass function
group
cluster
Detected baryons
(McGaugh
+ 2010)
Slide3
Groups are :1) Ideal systems to study baryonic physics (e.g., SN winds, cooling, AGN heating), which dominates the systematic uncertainties for cluster cosmology.The same baryonic physics is important to understand the formation and evolution of galaxies (most galaxies are in groups).
Stellar fraction(McGaugh + 2010)Slide4
Are groups gas / baryon poor
? Are groups metal poor ?Slide5
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 fractionSlide6
LX - T Groups(Sun+09), Chandra +REXCESS(Pratt+09, +10), XMM(both samples also agree well on other scaling relations)Bolometric< r500Bolometric
(0.15 r500, r500)2.912.85Slide7
Are groups gas poor
at large radii ?
Vikhlinin +
09; REXCESS (Pratt + 09); Sun + 09 Slide8
Humphrey et al. 2011, Chandra
Deep observations are required for gas at large radii !LX, 2500 / LX, 500 ~ 4/5vs.Mgas, 2500 / Mgas, 500 ~ 1/410121013
1014
1015M2500 or M500 (Mʘ)Slide9
Pressure content in
groups
Sun, Sehgal
+
2011
The key to understand the SZ power spectrum (from SPT and ACT)
a
s ~
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 Slide10
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 fraction
cosmic baryon fraction
(Lin+03; Gonzalez+07; Giodini+09 Sun+09; Vikhlinin+09)
stars
g
as + starsSlide11
Are groups gas / baryon poor
? Are groups metal poor ?Slide12
Baumgartner et al. 2005
Are groups metal
(iron) poor
?
Emission-weighted (
ASCA
)
M
gas
-weighted
Sun
et al.
2011
(also
see Rasmussen &
Ponman,
2009; Bregman + 2010)Slide13
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 …
a
bundance of
clustersSlide14
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
Slide15
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) .Slide16
The EndSlide17
Entropy scaling relations
(
Sun et al. 2009, 43 groups
; Vikhlinin et al. 2009, 14
clu.;
Pratt et al. 2010, 31
clu
.)
Slide18
Halo mass Stellar mass / Halo massHalo Stellar Fraction Slide19
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. 2011Slide20
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.)Slide21
1) No pretty Chandra images
2) Hydrostatic equilibrium mass 3) Selection bias 4) Correlated errorsSlide22
Are groups gas poor
at large radii ?
Vikhlinin +
09; REXCESS (Pratt + 09); Sun + 09
@
r
500Slide23
LX - T Groups(Sun+09), Chandra +REXCESS(Pratt+09, +10), XMMBolometric< r5000.5-2 keV< r500
Bolometric(0.15 r500, r500)0.5-2 keV(0.15 r500, r500)2.912.852.60
2.55