Scaling properties of a complete X-ray selected galaxy group sample

Abstract

Context. Upcoming X-ray surveys like eROSITA require precise calibration between X-ray observables and mass down to the lowmass regime to set tight constraints on the fundamental cosmological parameters. Since an individual mass measurement is only possible for relatively few objects, it is crucial to have reliable and clearly understood scaling relations that relate the total mass to easily observable quantities. Aims. The main goal of this work is to constrain the galaxy group scaling relations corrected for selection effects, and to quantify the influence of non-gravitational physics at the low-mass regime. Methods. We analyzed XMM-Newton observations for a complete sample of galaxy groups selected from the ROSAT All-Sky Survey and compared the derived scaling properties with a galaxy cluster sample. To investigate the role played by the different non-gravitational processes we then compared the observational data with the predictions of hydrodynamical simulations. Results. After applying the correction for selection effects (e.g., Malmquist bias), the L X -M relation is steeper than the observed one. Its slope (1.66 ± 0.22) is also steeper than the value obtained by using the more massive systems of the HIFLUGCS sample. This behavior can be explained by a gradual change of the true L X -M relation, which should be taken into account when converting the observational parameters into masses. The other observed scaling relations (not corrected for selection biases) do not show any break, although the comparison with the simulations suggests that feedback processes play an important role in the formation and evolution of galaxy groups. Thanks to our master sample of 82 objects spanning two order of magnitude in mass, we tightly constrain the dependence of the gas mass fraction on the total mass, finding a difference of almost a factor of two between groups and clusters. We also found that the use of different AtomDB versions in the calculation of the group properties (e.g., temperature and density) yields a gas fraction of up to 20% lower than an older version.

Extending theLX–Trelation from clusters to groups

“…Eckmiller et al (2011) show that there is a good agreement between clusters and groups for most scaling relations, albeit with increased intrinsic scatter on the group regime, which is not totally unexpected due to the complicated baryonic physics at play in low-mass systems. Recent results by Lovisari et al (2014), however, argue that while the observed scaling relations for galaxy groups are in agreement with those obtained for galaxy clusters, the scaling relation obtained after corrections for selection effects are consistent with a gradual steepening towards the low-mass regime.…”

“…It is an effect that has been shown to affect scaling relations, namely resulting in higher observed normalisations as compared to the actual normalisations in scaling relations for clusters (e.g. Ikebe et al 2002;Stanek et al 2006;Pratt et al 2009;Mantz et al 2010;Lovisari et al 2014). In this sample, we have applied an additional luminosity cut which could further contribute to the bias.…”

Sardinia Radio Telescope observations of Abell 194

“…The temperature profile and the cooling time of 21.6±4.41 Gyr determined by Lovisari et al (2015), and the temperature map by Bogdán et al (2011), indicate that Abell 194 does not harbor a cool core.…”

The long X-ray tail in Zwicky 8338

“…Also, comparing the measured X-ray flux of the Comet with those of small galaxy groups using the L − T relation from Lovisari et al (2015), we conclude a redshift range z = 0.036 +0.021 −0.012 , which also excludes this structure from being a background cluster.…”

“…The solar abundances are set to the values given by Asplund et al (2009). The influence of the abundance table, especially at lower plasma temperatures on the best-fit parameters, are shown, e.g., in Lovisari et al (2015). (Fasano et al 2006) in green.…”