The XXL Survey

Abstract

Context. An X-ray survey with the XMM-Newton telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg2 fields. Combining spectroscopic and X-ray observations in one field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature. Aims. Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature, T300 kpc, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, ⟨lnM200 | T300 kpc, z⟩. Methods. We applied an ensemble velocity likelihood to a sample of >1500 spectroscopic redshifts within 132 spectroscopically confirmed clusters with redshifts z < 0.6 to model, ⟨lnσgal | T300 kpc, z⟩, where σgal is the velocity dispersion of XXL cluster member galaxies and T300 kpc is a 300 kpc aperture temperature. To infer total halo mass we used a precise virial relation for massive halos calibrated by N-body simulations along with a single degree of freedom summarising galaxy velocity bias with respect to dark matter. Results. For the XXL-N cluster sample, we find σgal ∝ T300 kpc0.63±0.05, a slope significantly steeper than the self-similar expectation of 0.5. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift, 〈ln(E(z)M200/1014 M⊙)|T300 kpc, z〉 = πT + αT ln (T300 kpc/Tp) + βT ln (E(z)/E(zp)) using pivot values kTp = 2.2 keV and zp = 0.25, with normalization πT = 0.45 ± 0.24 and slope αT = 1.89 ± 0.15. We obtain only weak constraints on redshift evolution, βT = −1.29 ± 1.14. Conclusions. The ratio of specific energies in hot gas and galaxies is scale dependent. Ensemble spectroscopic analysis is a viable method to infer mean scaling relations, particularly for the numerous low mass systems with small numbers of spectroscopic members per system. Galaxy velocity bias is the dominant systematic uncertainty in dynamical mass estimates.

Scaling Properties of Galaxy Groups

“…Using a sample of 132 clusters (the majority of which have T x < 3 keV), ref. [153] found a relation of the form σ v ∝T 0.63±0.05…”

“…Note that the relation is fitted using an ensemble maximum likelihood method, with fitted slope in tension with the self-similar expectation. Since both velocity dispersion and X-ray temperature scales with total mass, one can combine the information to determine a useful mass calibration (e.g., Farahi et al 2018b). However, consideration must be given to velocity anisotropies during mass modelling using velocity information, which can vary for loose, compact and viralised groups (Mamon 1993).…”

Mass calibration of the CODEX cluster sample using SPIDERS spectroscopy – II. The X-ray luminosity–mass relation

“…Many different mass proxies have been used over the years, including thermal Sunyaev-Zeldovich effect (SZE) measurements (Staniszewski et al 2009;Planck Collaboration et al 2014;Hasselfield et al 2013), weak gravitational lensing features (Corless & King 2009;Becker & Kravtsov 2011;Dietrich et al 2018), cluster velocity dispersions (Biviano & Salucci 2006;Saro et al 2013;Capasso et al 2019b), and X-ray luminosity and temperature Mantz et al 2010). A combination of multiple, independent mass proxies help mitigate systematic errors (Bocquet et al 2015;McClintock et al 2018;Baxter et al 2018;Farahi et al 2018;Bocquet et al 2018). In a companion paper (Capasso et al 2019a, hereinafter C19) we performed the dynamical mass calibration exploiting the optical richness of a sample of 428 CODEX (COnstrain Dark Energy with Xray clusters; Finoguenov, in prep) clusters, constraining the amplitude of the λ-mass relation with a ∼12% accuracy.…”

The galaxy group NGC 507: newly detected AGN remnant plasma transported by sloshing

“…The analysis of the scaling relations of the X-ray properties with the dispersion velocity and with the profile of the dispersion velocity (Lovisari et al 2021) provides further support to the disturbed nature of the group. If we take the temperature of the system as measured in the annulus 0.15-0.5 R 500 equal to 1.19 keV, as a reference value, the NGC 507 group is a clear outlier in the σ − T relation (see for example Farahi et al 2018) as is located well above the expectation of a constant specific energy ratio, β spec = 1.…”