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Baryon content of galaxy groups

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.

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Baryon content of galaxy groups

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  1. 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)

  2. group Groups? Why do we care? cluster cluster group Mass function 1015 Mʘ 1013Mʘ Detected baryons (McGaugh + 2010)‏ Galaxy groups are the smallest halos where the bulk of baryons are accounted for .

  3. 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)

  4. Are groups gas / baryon poor ? Are groups metal poor ?

  5. Groups are gas poor around the center cosmic baryon fraction cosmic baryon fraction Sun + 2009 ; Vikhlinin + 2009, Chandra samples (r2500 ~ 1/3 rvir , r500 ~ 2/3 rvir)

  6. Bolometric < r500 LX - T Groups (Sun+09), Chandra + REXCESS (Pratt+09, +10), XMM (both samples also agree well on other scaling relations) 2.91 Bolometric (0.15 r500, r500) 2.85

  7. Are groups gas poor at large radii ? Vikhlinin + 09; REXCESS (Pratt + 09); Sun + 09

  8. Deep observations are required for gas at large radii ! LX, 2500 / LX, 500 ~ 4/5 vs. • Mgas, 2500 / Mgas, 500 ~ 1/4 1013 1015 1012 1014 M2500 or M500 (Mʘ) Humphrey et al. 2011, Chandra

  9. Pressure content in groups 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 Sun, Sehgal +2011

  10. 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 gas + stars stars (Lin+03; Gonzalez+07; Giodini+09 Sun+09; Vikhlinin+09)

  11. Are groups gas / baryon poor ? Are groups metal poor ?

  12. Are groups metal (iron) poor ? Emission-weighted (ASCA) Mgas-weighted Sun et al. 2011 • (also see Rasmussen & Ponman, 2009; Bregman + 2010) Baumgartner et al. 2005

  13. Group gas is also iron poor around the center If all metals produced were kept … abundance of clusters Why ? metal loss at early time (e.g., SN winds, Quasars) late time (e.g., radio AGN)

  14. Looking forward … 1) Hydrostatic equilibrium mass to be calibrated 2) Selection bias ? --- (try different samples) 3) Extending to lower masses ! (low nHand back.) 4) Go beyond r500 (e.g., stacking) • 5) More theory / simulation work

  15. 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) .

  16. The End

  17. Entropy scaling relations (Sun et al. 2009, 43 groups; Vikhlinin et al. 2009, 14 clu.; Pratt et al. 2010, 31 clu.)‏

  18. Halo Stellar Fraction Stellar mass / Halo mass Halo mass

  19. 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

  20. Why are groups metal poor? Systematic issues: 1) “iron bias” (Buote 2000) for group cool cores, but NOT the reason here 2) “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.)

  21. 1) No pretty Chandra images 2) Hydrostatic equilibrium mass 3) Selection bias 4) Correlated errors

  22. Are groups gas poor at large radii ? @ r500 Vikhlinin + 09; REXCESS (Pratt + 09); Sun + 09

  23. Bolometric < r500 0.5-2 keV < r500 LX - T Groups (Sun+09), Chandra + REXCESS (Pratt+09, +10), XMM 2.60 2.91 Bolometric (0.15 r500, r500) 0.5-2 keV (0.15 r500, r500) 2.85 2.55

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