The 2dF Galaxy Redshift Survey: correlation with the ROSAT-ESO flux-limited X-ray galaxy cluster survey

Abstract

The ROSAT-European Southern Observatory (ESO) flux-limited X-ray (REFLEX) galaxy cluster survey and the Two-degree Field Galaxy Redshift Survey (2dFGRS), respectively, comprise the largest, homogeneous X-ray selected cluster catalogue and completed galaxy redshift survey. In this work, we combine these two outstanding data sets in order to study the effect of the large-scale cluster environment, as traced by X-ray luminosity, on the properties of the cluster member galaxies. We measure the Lₓ−σᵣ relation from the correlated data set and find it to be consistent with recent results found in the literature. Using a sample of 19 clusters with Lₓ ≥ 0.36 × 10⁴⁴ erg s⁻¹ in the 0.1–2.4 keV band, and 49 clusters with lower X-ray luminosity, we find that the fraction of early spectral type (η=−1.4), passively evolving galaxies is significantly higher in the high-Lₓ sample within R₂₀₀. We extend the investigation to include composite bⱼ cluster luminosity functions, and find that the characteristic magnitude of the Schechter-function fit to the early-type luminosity function is fainter for the high-Lₓ sample compared to the low-Lₓ sample (ΔM*= 0.58 ± 0.14). This seems to be driven by a deficit of such galaxies with Mbⱼ∼−21. In contrast, we find no significant differences between the luminosity functions of star-forming, late-type galaxies. We believe these results are consistent with a scenario in which the high-Lₓ clusters are more dynamically evolved systems than the low-Lₓ clusters.

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