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Metallicity Structure in X-ray Bright Galaxy Groups

This study investigates the radial distribution of metals in dynamically relaxed galaxy groups through X-ray spectroscopy. The behavior of supernova products outside group cores, Fe-content in the outskirts, and abundance profiles are examined to compare with enrichment models.

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Metallicity Structure in X-ray Bright Galaxy Groups

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  1. Metallicity structure in X-ray bright galaxy groups- Radial distribution of metals in dynamically relaxed groups Jesper Rasmussen (Univ. of Birmingham) with Trevor Ponman

  2. X-ray spectroscopy of hot group gas – issues to address: • Behaviour of SN II products outside group cores? • Fe-content in outskirts? Need to determine ZFe at large radii, to estimate total iron masses & compare to enrichment models. • Abundance profiles: Also signatures of galactic feedback – can we disentangle AGN (redistribution of gas) from supernova (source of metals) feedback ? Background Metal abundances in clusters well-studied, situation in groups much more unclear. But significant fraction of baryons (and galaxies) are in groups: Chemical evolution of the Universe ↔ content and distribution of metals in groups.

  3. Selection criteria: “brightness” > 6000 photons to enable detailed spatially resolved spectroscopy. D > 20 Mpc to go well outside the group core. Undisturbed morphology to exclude groups with recent merger activity. Sample and analysis Basis: Chandra archival data of GEMS groups (Osmond & Ponman 2004). 1-T and 2-T plasma model fits to spectra in radial bins with ≥ 2000 net cts. Free parameters: T, ZFe, ZSi, Zothers (vapec model in xspec with solar abundances from Grevesse & Sauval 1998). All radii converted into r/r500, using (Evrard et al. 1996) r500 = (124/H0) × (‹TX›/10 keV)1/2

  4. Groups relaxed (supports use of 1-D profiles), have a cool core extending beyond central galaxy. Surface brightness & temperature structure 0.3-2 keV adaptively smoothed images.

  5. Chandra + XMM results for 22 groups: Correlation test: Kendall's τ = 0.12 (significance: 0.8σ). So no indication that Fe preferentially ejected from lower-mass systems within this TX-range. <T> and <Z> measured within 0.1-0.3 r500 : A correlation between ‹TX› and ‹Z› ? Do groups show lower abundances than clusters? Real effect (e.g. ejection of metals from group potentials) or induced by systematics ? - gas in clusters detected to relatively larger radii. - importance of Fe bias increasing at low TX(Buote 2000).

  6. Fe profiles: Central excesses. Profiles bottoming out towards ~ 0.1 Z, lower than in clusters (Böhringer et al. 2004; Tamura et al. 2004). Si profiles: Similar to ZFe(r) in group cores. Smaller radial variation at large r. Increase in outer parts in some groups. Fe and Si profiles

  7. Metal production dominated by SN Ia in central regions. Si/Fe: In group cores generally consistent with local (Solar) SN mixture and IMF. Silicon-to-iron ratio SN II ZSi/ZFe: signature of relative importance of SN II vs SN Ia. Adopted SN model abundances: Baumgartner et al. (2005). Based on yields from Nomoto et al. (1997) + Salpeter IMF. SN Ia

  8. Fe declines outside group core at > 4σ significance, with log (ZFe) ∝−0.7 log (r/r500). Value at r500 is ~ 0.1 Z Si is almost constant with r outside core (declines at 0.6σ) Combining the results... All 200 measurements:

  9. In group cores: Both Fe, Si roughly uniform. SN Ia dominate, probably from central, bright galaxy. SN II contribution required at all radii, dominate at large radii. Due to early enrichment from less massive galaxies? ....and binning them too

  10. Although <Z> ≈ 0.3Z, as in clusters, Fe abundance at large radii lower than in clusters by factor of ~2. Total MFe in gas mainly determined by ZFe at large r,  MFe/LB smaller in groups than clusters (Renzini 1997). But <Z> does not correlate with depth of grav. potential (TX) & baryon fractions in some T ~ 1-2 keV groups are near-cosmic (Buote et al. 2004, Rasmussen & Ponman 2004) Ejection of (enriched) gas via AGN/SN winds not globally important? Implications • Significant fraction of Fe in groups not accounted for? • non-central enrichment inefficient? • ejection of metals only efficient in outskirts and/or accompanied by very low “mass-loading”, independently of TX ?

  11. Fe profiles show central excesses, but flatten out to ~ 0.1 Z, lower than in clusters (e.g. Tamura et al. 2004). Si nearly constant with r outside group core. “Global” mean of ZSi/ZFe ≈ 1.3 solar – agrees with cluster results. But clear dichotomy in Si/Fe distribution. Enrichment in group cores marginally dominated by SN Ia. SN II contribution required at all radii, and dominates strongly in outer parts. Low Z at large radii challenging simple enrichment models if baryon fractions are near-cosmic (Buote et al. 2004). Planned work: - Investigate correlations with radio luminosity of central galaxy. - perform detailed tests of enrichment/feedback models. Summary & outlook

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