AGN Heating of the Intergalactic Medium in Galaxy Groups

1. AGN Heating of the Intergalactic Medium in Galaxy Groups Eric M. Wilcots University of Wisconsin-Madison Kelley M. Hess (Wisconsin), Jana Grcevich (Michigan) Eric M. Wilcots

2. Why Galaxy Groups? • ~70% of nearby galaxies reside in groups • What is the impact of the group environment on galaxy evolution? • What is the impact of galaxy evolution on the group environment? • Groups define the large scale structure • What can the impact of AGN in groups tell us about the growth and evolution of large scale structure? Eric M. Wilcots

3. What are Galaxy Groups? • 3-10 members with MV < -19 within a radius of 0.5 Mpc (Zirbel 1997) • “poor cluster” (Bahcall 1980) • ~30 members with m such that m3 < m < (m3+2) • m3 is the magnitude of the 3rd brightest member • N > 4 with 200 km s-1 < σ < 400 km s-1 (Carlberg 2001) • Mhalo ~ 1012-1014 Mo (Eke 2004) Eric M. Wilcots

4. What are galaxy groups? • GEMS Sample (Brough et al. 2006) • N ~ 3-20 • σ ~ 28 – 430 km s-1 • R500 ~ 0.22-0.56 Mpc • Radius at which density = 500 x ρcrit • log LX (erg s-1) ~ 40.7-42.11 • 2/16 with upper limits ~40.5 Groups have long been defined by the luminosity and extent of their X-ray emission Eric M. Wilcots

5. Groups aren’t clusters…. • Variations in optical luminosity function, HI mass function… • Group velocity dispersion ~ internal velocity dispersion of individual galaxies • Ram pressure stripping & “harrassment” less likely • Galaxies more likely to be falling into a “dense” environment for the first time • Galaxy-galaxy mergers more likely in groups than clusters Eric M. Wilcots

6. What do jets have to do with galaxy groups? Eric M. Wilcots

7. X-ray Emission from Groups Mulchaey et al. 2003 Eric M. Wilcots

8. X-ray properties Mulchaey et al. 2003 Eric M. Wilcots

9. Heating Problem in Galaxy Groups • Cosmology  pure gravitational infall should yield (purely thermal): • TX ~ σ2 and LX ~ TX2 • Generally true for large clusters; not true for groups • ROSAT/CXO/XMM observations of groups • Lx ~ TXb where b > 2  implies additional heating by non-gravitational means  Lx~Tx2.7 Eric M. Wilcots

10. Heating Problem = Excess Entropy • S = T/ne2/3 (T = gas temperature) • Excess Entropy • Manifests as flatter density profile for the X-ray emitting gas • Makes groups less luminous than expected • Drives deviations in Lx-T relationship • Conclusion  some non-gravitational “preheating” of intragroup medium Eric M. Wilcots

11. Excess Entropy in Galaxy Groups Jeltema et al. 2006 Intermediate redshift groups Dashed line = pure gravitational, self-similar with clusters Eric M. Wilcots

12. X-ray observations of galaxy groups require non-gravitational heating of the intragroup medium. Eric M. Wilcots

13. Gas Content of The Local Group • Gas-rich spirals • Gas-rich irregulars • Tidal Debris/HVCs Total HI Mass of Local Group ~ 10.13 (log MHI) ~ 10% Mstellar, ≤ 1% of Mdynamical Eric M. Wilcots

14. The Evolution of the Gas Content of Groups (Freeland et al 2007) • Interaction rate much higher in spiral-dominated groups. • Spiral dominated/HI rich  elliptical dominated/X-ray rich • “Unattached” HI clouds (merger remnants) more common in elliptical dominated groups • Conversion of neutral gas into hot gas takes place with the intragroup medium and not in individual galaxies Eric M. Wilcots

15. Gas Properties of X-ray Luminous Galaxy Groups: Helsdon, Ponman, Mulchaey 2006 Mgas ~ 1-4 x 1011 M0 10 times MHI for groups with similar dynamical mass Eric M. Wilcots

16. Evolution of the gas content of galaxy groups • Dynamically young systems  most of the gas mass remains undetected (WHIM??) • Dynamically evolved systems  most of the gas mass exists as X-ray emitting intragroup medium • Some sort of heating mechanism is required to understand the evolution of the gas content of galaxy groups Eric M. Wilcots

17. What about AGN? Eric M. Wilcots

18. A statistical approach…. • 2dF Galaxy Redshift Survey • 15000 square degrees • 2.1 x 106 galaxies • 2dF Galaxy Group catalog (Eke et al 2004) • 2 x 105 groups • 2dFGRS/NVSS correlation (Sadler et al. 2002) • ~4000 matched sources; 2200 AGN (50 mJy) Eric M. Wilcots

19. AGN in 2dFGRS Groups(0.03 < z < 0.3) • 70% of AGN reside in 2dFGRS groups • 7.7% of groups with N > 4 have an AGN (4.5% of all groups) • <<1% of groups have more than one AGN It is not obvious that, statistically, AGN have a tremendous impact on the overall population of groups Eric M. Wilcots

20. A More Direct Statistical Approach..(Croston et al. 2004) Eric M. Wilcots

21. A Direct Approach Is there evidence for past heating of the intragroup medium in the form of low frequency radio relics? Eric M. Wilcots

22. A Direct Approach • Low frequency (600/300 MHz) mapping of x-ray luminous/radio loud galaxy groups • Dwarakananth & Nath (2007) found no extended 327 MHz emission in X-ray luminous/radio quiet groups 327 MHz GMRT Map (Hess & Wilcots) Eric M. Wilcots

23. Eric M. Wilcots

24. Conclusions • X-ray observations require extra non-gravitational heating • Comparison of HI and X-ray gas content of groups at different dynamical states requires some heating mechanism • Direct radio observations of X-ray luminous groups with radio galaxies are currently a mixed bag… Eric M. Wilcots