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Keywords:

  • galaxies: clusters: general;
  • cosmology: observations;
  • X-rays: galaxies: clusters

ABSTRACT

We study the thermodynamic properties of the hot gas in a sample of groups in the 0.012–0.024 redshift range, using XMM–Newton observations. We present measurements of temperature, entropy, pressure and iron abundance. Non-parametric fits are used to derive the mean properties of the sample and to study dispersion in the values of entropy and pressure. The scaling of the entropy at 0.2r500 matches well the results of Ponman, Sanderson & Finoguenov. However, compared to cool clusters, the groups in our sample reveal larger entropy at inner radii and a substantially flatter slope in the entropy in the outskirts, compared to both the prediction of pure gravitational heating and observations of clusters. This difference corresponds to the systematically flatter group surface brightness profiles, reported previously. The scaled pressure profiles can be well approximated with a Sérsic model with n= 4. We find that groups exhibit a systematically larger dispersion in pressure, compared to clusters of galaxies, while the dispersion in entropy is similar.