Galaxy groups: X-ray scaling relations, cool cores and radio AGN Ming Sun (UVA) (M. Voit, W. Forman, P. Nulsen, M. Donahue, C. Jones, A. Vikhlinin, C. Sarazin )
Outline: 1) Scaling relations and baryon physics (entropy, gas fraction and abundance) 2) AGN heating in individual groups (Strong radio AGN in non-cool-core! hunting for strong shocks etc.)
Galaxy groups? Why do we care? 10 Msun 13 1015 Msun 1) Galaxy groups are abundant and most galaxies are in groups; building blocks of clusters But more importantly...
Groups are ideal systems to study baryon physics! *) Baryon physics (e.g., cooling, AGN heating, Supernova winds) begins to be dominant in groups, need to understand them in groups to better use clusters to do precision cosmology. *) The same baryon physics is important to understand the formation and evolution of galaxies and their central SMBHs. Voit 2005
BHs can really mess up group gas 1) Radio AGN heating energy: ktbh, all ℇ (0.2% f* M500) c2 / 1.5 N M500-0.43 (all Gs) ktbh, BCG ℇ (0.2% f*,bcg M500) c2 / 1.5 N M500-0.88 (BCG) 2) Total thermal energy of the ICM: KTth = kt M500 0.61 3) Total potential energy of the gas: ktpo G fgas M5002 / r500 / 1.5 N M500 / r500 M5002/3 (ℇ 0.1 efficiency, half of BH mass from radio AGN feedback, N = fgas M500 / mu ) (using scaling relations in Lin & Mohr, 2003 & 2004; Sun et al. 2009)
Baryon physics: Cooling: X-ray cool core, star-formation --- baryon fraction locked into stars Preheating: Winds before collapses (Evrard's talk) Heat conduction: much weaker in groups, (T5/2 for classical conduction) AGN heating SN & Stellar winds
Group scaling relations and comparison with simulations The group sample (Sun et al. 2009) 43 groups (0.015 < z < 0.12, kt=0.7 2.7 kev) from the Chandra archive (61 observations, almost a month of Chandra observing) Not a homogeneous sample! However... Previous work: Ponman, Mulchaey, Buote, Finoguenov, Mahdavi, Pratt, Gastaldello Other recent sample studies: Gastaldello et al. (2007): Concentration parameter, T and gas fraction Rasmussen & Ponman (2007, 2010): T and abundance Johnson, Ponman & Finoguenov (2010): 2D mapping, entropy In this talk: I will focus on Entropy, gas fraction and abundance
M500 T500 and M500 YX,500 relations to groups Sun et al. (2009); red cluster points from Vikhlinin et al. (2009)
Temperature profiles (43 groups) Sun et al. 2009 Clusters Groups Cluster data: Leccardi & Molendi 2009 Group data: Sun et al. 2009 Simulations by Fabjan et al. 2010
ICM Entropy (K) profiles Entropy profiles show extra heat throughout groups Entropy profile from only gravity (Voit et al. 2005) Sun et al. 2009
Entropy Temperature relations of groups
Entropy Temperature relations 12% scatter (51) 8% scatter (79) r500 ~ 452 kpc at kt = 1 kev r1000 ~ 335 kpc at kt = 1 kev gravity only 10% scatter (88) 32% scatter (88) r2500 ~ 207 kpc at kt = 1 kev 0.15 r500 ~ 68 kpc at kt = 1 kev gravity only gravity only (Sun et al. 2009, 43 groups, Chandra; Vikhlinin et al. 2009, 14 clusters, Chandra; Pratt et al. 2010, 31 clusters, XMM)
How to interpret the K T relations? (Fabjan et al. 2010) (McCarthy et al. 2010) From comparison with simulations (Borgani & Viel 2009; Fabjan et al. 2010; McCarthy et al. 2010), what we know so far: 1) AGN heating is required! Only pre-heating may not work. 2) AGN heating needs to be tuned (detail on the energy coupling and burst history)
Halo gas fraction 1) The amount of hot gas is affected by cooling / heating. 2) Low-mass halos possess less hot gas, esp. within r2500 (~ 1/3 rvir), --- something stopping gas to settle down to the center! (mass bias at r500, 30% mass bias --- ~ 12% decrease on fgas) cosmic baryon fraction 0.16-0.22 cosmic baryon fraction within r2500 groups within r500 Sun et al. 2009; Vikhlinin et al. 2009
How to understand the observed gas fraction? Simulations: if radio AGN heating not only prevents cooling in cool cores, but also inject sufficient energy to expel gas from the halo ejected Puchwein, Sijacki & Springel 2008 hot Bower et al. 2008
One more simulation on gas fraction Data: Sun et al. (2009); Simulations:McCarthy et al. 2010
How to reach the Universal baryon fraction (0.167+/-0.006) in groups? 1) Increasing gas fraction at r > r500. (assuming NFW profile, X-ray gas follows r-3β at large radii) for β=0.5, 75% increase from r500 at r101, 36% at r200. 2) Increasing fraction of intracluster light in groups? (still controversial; one promising way it with SN, McGee & Balogh 2010) Lin & Mohr 2004 Gonzalez et al. 2008 Sun et al. 2009
ICM abundance (iron) Emission-weighted MFe / Loptical ratio and Fe abundance Baumgartner et al. 2005 Mgas-weighted Renzini 1997 Important to know abundance at r > r2500, however, We still know little about the abundance at ~ r500! Rasmussen & Ponman (2009)
39 groups from Sun et al. (2009) Anders & Grevesse (1989) solar table
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)? (note a similar issue with the low-lx ellipticals) 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.)
Group samples with better selection functions: 1) Buote et al. 15 systems (kt = 1 3 kev) selected from NORAS, Flux limited, ACIS-S observations, don't cover r_500, relaxed ones included in Sun et al. (2009) 2) REGOS4 sample (MS et al.): an LX selected sample 3) optical selected groups SDSS-C4 (MS et al.) Fossil groups from MaxBCG (Dupke, Rykoff) 4) A potential project to better remove the X-ray bias on fgas :
REGOS4 (a REpresentative GrOup Sample from the 400 deg2 survey) 1) A sample of 12 groups LX-selected from the 400 deg2 survey (Vikhlinin, Burenin et al.), extended the REXCESS (Böhringer, Pratt et al.) luminosity threshold by a factor of 10 (PI: MS) 2) We have obtained 280 ks Chandra time + 430 ks XMM time, plus ~ 200 ks in the archives, including a complete Chandra coverage 3) NIR (NEWFIRM), optical and radio follow-ups are ongoing
AGN heating in group cool cores Birzan et al. 2008 Red: kt < 2 kev Blue: kt > 2 kev Sun 2009
iclicker Q: Which cluster BCG has a stronger radio AGN? Cooling time at 10 kpc: 0.3 Gyr (A478) vs. 17 Gyr (A3391)
A3391 A478 The existence of coronae allows energy ejection to the surrounding ICM in the absence of large cool cores.
Decoupled from feedback loop! AGN-regulated feedback loop Rafferty et al. 2006 Red: kt < 2 kev, Blue: kt > 4 kev Green: kt =2-4 kev (Sun 2009)
Optically selected groups with strong central radio AGN * Selected from the SDSS-C4-DR5 sample (Miller et al. 2004) (1713 clusters) * z<0.1 groups (expected kt <= 2 kev) * Selected seven BCGs with the most luminous radio AGN (L1.4 GHz = 6.5 10 x 1024 W Hz-1) * Six groups approved for 156 ks in Chandra cycle 11 (PI: MS) 50 kpc
1) Five observed so far, all of them are real groups with diffuse X-ray emission traced to r > r2500. 2) None of the observed five has a large cool core, all consistent with a corona 3) kt higher than expected, 4 of 5 at ~ 2.5 kev
Hydra A Ma = 1.41 (McNamara et al. 2005) Ma = 1.65 (Nulsen et al. 2005) Ma ~ 1.3 (Nulsen et al. 2005) Ma = 1.2 (Fabian et al. 2006) Ma = 8.5 (Kraft et al. 2003; Croston et al. 2009) Ma ~ 4 (Croston et al. 2007) Shock velocities range from 850-2400 km/s, while cs = 515 km/s @ 1 kev
Optical emission-line nebulae in group cool cores (PI: MS)
Conclusions: 1) Groups are important and ideal systems to study baryon physics (AGN heating, pre-heating, cooling etc.) --- severe weather (but subtle features) in groups! 2) General studies of extra heat (extra entropy), gas (baryon) fraction and abundance carry important information on AGN heating and other baryon physics, while work on individual systems with cavities and shocks also provides important information, e.g., AGN energetic, duty cycle, jet precession and gas cooling. More to come...