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Investigating Cool Cores in Galaxy Groups: An Analysis of AGN Heating and Cooling Flows

This study explores the dynamics of galaxies within groups, emphasizing X-ray observations from Chandra and XMM-Newton. We aim to understand how AGN heating affects cooling flows in different environments, specifically in elliptical-dominated groups. The research considers 23 groups from the XMM archive and 18 from Chandra, utilizing advanced spectral analysis to derive profiles for mass, entropy, and cooling time. Highlighted cases such as NGC 5044 and NGC 4636 reveal the complex interplay between gas cooling, metal enrichment, and AGN feedback mechanisms.

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Investigating Cool Cores in Galaxy Groups: An Analysis of AGN Heating and Cooling Flows

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  1. Cool Cores in Galaxy Groups EwanO’Sullivan Harvard-Smithsonian Center for Astrophysics In Collaboration with T. J. Ponman (University of Birmingham), J. Vrtilek & L. P. David (CfA), A. J. R. Sanderson (University of Illinois) The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  2. Introduction • The majority of galaxies in the universe are found in galaxy groups (Tully 1987), and many elliptical- dominated groups have massive hot gas halos (Mulchaey 2003). • A general X-ray study of galaxy groups with Chandra and XMM-Newton (and ROSAT), focusing particularly on cooling and feedback processes Questions • It is now clear that AGN heating stops cooling flows in clusters - is this also true in groups? • How does group gas become enriched with metals? The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  3. Groups Sample • 23 groups from XMM archive,18 from Chandra The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  4. Analysis • 2-D multi-component surface brightness fits • Radial spectral profiles (circular or elliptical, deprojected) • Derive mass, entropy, cooling time, etc. profiles, assuming hydrostatic equilibrium • What about disturbed systems? • Adaptively binned spectral maps - each pixel represents a separate spectral fit, but fits are not independent. Behaviour comparable to adaptive smoothing Current focus on XMM data, work in progress! The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  5. NGC 5044 From ROSAT (David et al 1994) • Cooling flow (20 M/yr) • Cooling wake indicates ~100 km/s motion of galaxy From Chandra / XMM: • No CF, no gas kT<0.6 keV (Tamura et al 2003; Buote et al 2003) Our XMM analysis: • No CF, but cooling time less than 109 yrs • Minimal AGN activity, so what prevents cooling? • Is cooling wake seen? Deprojected temperature Gas cooling time Deprojected abundance The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  6. Cooling wake  XMM X-ray image with optical contours Temperature map The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  7. NGC 4636 • Jones et al (2002) use Chandra to find ‘spiral arms’ in core • Shocks from AGN outburst? • Ohto et al (2003) find high kT, excess NH west of core • Cavity blown by AGN jets during previous outburst? Chandra image with VLA-First contours The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  8. Chandra image XMMtemperature • Cavity to E clearly visible • SW ‘Spiral arm’ marks cavity boundary • Highest abundance gas outside galaxy core? Complex spectra… XMM abundance The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  9. NGC 4636 spectral maps XMM Temperature XMM Abundance • Hot gas surrounds core on N and E sides • Highest abundances to SW The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  10. NGC 4636 southwest region • Plume of cool gas to SW with high abundance • AGN driving galaxy/group gas mixing? XMM Temperature XMM Abundance The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  11. NGC 507 • ROSAT shows strong cooling in core (Kim & Fabbiano 1995) • FR-I radio galaxy (Parma et al 1986) • Paolillo et al (2003) find X-ray / radio structure correlated but no CF • AGN power sufficient to stop cooling • Kraft et al (2004) find abundance edge NE of core The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  12. XMM gaussian smoothed XMM temperature DSS optical XMM abundance The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  13. Bright groups comparison • Comparable Mtotal, Mgas profiles • Large difference in kT, central density, Entropy • NGC 507 AGN most active, NGC 4636 activity beginning • AGN cycle governs core entropy? The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  14. AWM 4 & MKW 4: poor clusters • ~2.5 keV systems chosen to be regular, undisturbed • Very large central dominant galaxies • NGC 4073 in MKW4 is radio quiet • NGC 6051 in AWM4 has 100 kpc radio jets The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  15. AWM 4 • Relaxed system, SB profile well described by two -models • Isothermal kT profile • kT and abundance clearly affected by AGN activity - cavity to E, shock and high abundance to NW XMM temperature XMM abundance The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  16. MKW 4 • SB fits show cluster is asymmetrical • Strong kT drop in core but no gas <0.5 keV XMM temperature XMM abundance • Maps show highest abundances in core and to SE, where SB profile shows steepest drop The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  17. MKW 4 / AWM 4 comparison • Very similar mass profiles • MKW4 has cooler, denser, more gas-rich core • Rapid cooling • Gas fraction step in AWM 4  Gas pushed out by AGN The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  18. AWM 4 / MKW 4 summary • Slight difference in core Mtotal caused by difference in BCG mass (factor ~2) • Remaining differences caused by AGN cycle - AWM 4 isothermal because of AGN heating - MKW 4 is cooling, soon to trigger AGN? • Current radio power in AWM 4 ~1041 erg/s, but expect mechanical power to be up to 104 times greater • Energy required to raise MKW 4 temperature to that of AWM 4: ~9x1058 erg or ~3x1043 erg/s for 100 Myr - reasonable for AGN The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

  19. Conclusions • Cooling Flow / AGN connection holds across wide range of mass scales (1 keV groups to massive clusters) • Enrichment of groups through AGN galaxy / group gas mixing likely (at least in central regions) • AGN outbursts probably a major source of energy feedback in groups as well as clusters The Environments of Galaxies: from Kiloparsecs to Megaparsecs August 2004

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