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Title: A uniform metallicity in the outskirts of massive, nearby galaxy clusters

Abstract

Suzaku measurements of a homogeneous metal distribution of Z ~ 0:3 Solar in the outskirts of the nearby Perseus cluster suggest that chemical elements were deposited and mixed into the intergalactic medium before clusters formed, likely over 10 billion years ago. A key prediction of this early enrichment scenario is that the intracluster medium in all massive clusters should be uniformly enriched to a similar level. Here, we confirm this prediction by determining the iron abundances in the outskirts (r > 0:25r200) of a sample of ten other nearby galaxy clusters observed with Suzaku for which robust measurements based on the Fe-K lines can be made. Across our sample the iron abundances are consistent with a constant value, ZFe = 0:316 ± 0:012 Solar (Χ 2 = 28:85 for 25 degrees of freedom). This is remarkably similar to the measurements for the Perseus cluster of ZFe = 0:314±0:012 Solar, using the Solar abundance scale of Asplund et al. (2009).

Authors:
 [1];  [2];  [3];  [4];  [1]
  1. Stanford Univ., CA (United States)
  2. Masaryk Univ (Czech Republic); Hiroshima Univ. (China); MTA-Eotvos University Lendulet Hot Universe Research Group, Budapest (Hungary)
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States)
  4. Inst. of Space and Astronautical Science (ISAS) (Japan)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1390597
Grant/Contract Number:
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 470; Journal Issue: 4; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; clusters: intracluster medium; galaxies: X-rays: galaxies: clusters

Citation Formats

Urban, O., Werner, N., Allen, S. W., Simionescu, A., and Mantz, A.. A uniform metallicity in the outskirts of massive, nearby galaxy clusters. United States: N. p., 2017. Web. doi:10.1093/mnras/stx1542.
Urban, O., Werner, N., Allen, S. W., Simionescu, A., & Mantz, A.. A uniform metallicity in the outskirts of massive, nearby galaxy clusters. United States. doi:10.1093/mnras/stx1542.
Urban, O., Werner, N., Allen, S. W., Simionescu, A., and Mantz, A.. 2017. "A uniform metallicity in the outskirts of massive, nearby galaxy clusters". United States. doi:10.1093/mnras/stx1542.
@article{osti_1390597,
title = {A uniform metallicity in the outskirts of massive, nearby galaxy clusters},
author = {Urban, O. and Werner, N. and Allen, S. W. and Simionescu, A. and Mantz, A.},
abstractNote = {Suzaku measurements of a homogeneous metal distribution of Z ~ 0:3 Solar in the outskirts of the nearby Perseus cluster suggest that chemical elements were deposited and mixed into the intergalactic medium before clusters formed, likely over 10 billion years ago. A key prediction of this early enrichment scenario is that the intracluster medium in all massive clusters should be uniformly enriched to a similar level. Here, we confirm this prediction by determining the iron abundances in the outskirts (r > 0:25r200) of a sample of ten other nearby galaxy clusters observed with Suzaku for which robust measurements based on the Fe-K lines can be made. Across our sample the iron abundances are consistent with a constant value, ZFe = 0:316 ± 0:012 Solar (Χ2 = 28:85 for 25 degrees of freedom). This is remarkably similar to the measurements for the Perseus cluster of ZFe = 0:314±0:012 Solar, using the Solar abundance scale of Asplund et al. (2009).},
doi = {10.1093/mnras/stx1542},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 4,
volume = 470,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
Free Publicly Available Full Text
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  • Suzaku measurements of a homogeneous metal distribution ofmore » $$Z\sim0.3$$ Solar in the outskirts of the nearby Perseus cluster suggest that chemical elements were deposited and mixed into the intergalactic medium before clusters formed, likely over 10 billion years ago. A key prediction of this early enrichment scenario is that the intracluster medium in all massive clusters should be uniformly enriched to a similar level. Here, we confirm this prediction by determining the iron abundances in the outskirts ($$r>0.25r_{200}$$) of a sample of ten other nearby galaxy clusters observed with Suzaku for which robust measurements based on the Fe-K lines can be made. Across our sample the iron abundances are consistent with a constant value, $$Z_{\rm Fe}=0.316\pm0.012$$ Solar ($$\chi^2=28.85$$ for 25 degrees of freedom). This is remarkably similar to the measurements for the Perseus cluster of $$Z_{\rm Fe}=0.314\pm0.012$$ Solar, using the Solar abundance scale of Asplund et al. (2009).« less
    Cited by 1
  • We have studied the effects of electron-ion non-equipartition in the outer regions of relaxed clusters for a wide range of masses in the LAMBDACDM cosmology using one-dimensional hydrodynamic simulations. The effects of the non-adiabatic electron heating efficiency, beta, on the degree of non-equipartition are also studied. Using the gas fraction f{sub gas} = 0.17 (which is the upper limit for a cluster), we give a conservative lower limit of the non-equipartition effect on clusters. We have shown that for a cluster with a mass of M{sub vir} approx 1.2 x 10{sup 15} M{sub sun}, electron and ion temperatures differ bymore » less than a percent within the virial radius R{sub vir}. The difference is approx20% for a non-adiabatic electron heating efficiency of beta approx 1/1800 to 0.5 at approx1.4R{sub vir}. Beyond that radius, the non-equipartition effect depends rather strongly on beta, and such a strong dependence at the shock radius can be used to distinguish shock heating models or constrain the shock heating efficiency of electrons. With our simulations, we have also studied systematically the signatures of non-equipartition on X-ray and Sunyaev-Zel'dovich (SZ) observables. We have calculated the effect of non-equipartition on the projected temperature and X-ray surface brightness profiles using the MEKAL emission model. We found that the effect on the projected temperature profiles is larger than that on the deprojected (or physical) temperature profiles. The non-equipartition effect can introduce a approx10% bias in the projected temperature at R{sub vir} for a wide range of beta. We also found that the effect of non-equipartition on the projected temperature profiles can be enhanced by increasing metallicity. In the low-energy band approx<1 keV, the non-equipartition model surface brightness can be higher than that of the equipartition model in the cluster outer regions. Future X-ray observations extending to approxR{sub vir} or even close to the shock radius should be able to detect these non-equipartition signatures. For a given cluster, the difference between the SZ temperature decrements for the equipartition and the non-equipartition models, deltaDELTAT{sub SZE}, is larger at a higher redshift. For the most massive clusters at z approx 2, the differences can be deltaDELTAT{sub SZE} approx 4-5 muK near the shock radius. We also found that for our model in the LAMBDACDM universe, the integrated SZ bias, Y{sub non-eq}/Y{sub eq}, evolves slightly (at a percentage level) with redshift, which is in contrast to the self-similar model in the Einstein-de Sitter universe. This may introduce biases in cosmological studies using the f{sub gas} technique. We discussed briefly whether the equipartition and non-equipartition models near the shock region can be distinguished by future radio observations with, for example, the Atacama Large Millimeter Array.« less
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  • Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggested that self-similarity may be broken in the outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean densitymore » of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter (DM) perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-DM density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev–Zel’dovich effect, and their applications to cosmology.« less