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Journal Article

The XXL Survey. XLII. The LX − σv relation of galaxy groups and clusters detected in the XXL and GAMA surveys


Ramos-Ceja,  M. E.
High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society;

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Giles, P. A., Robotham, A., Ramos-Ceja, M. E., Maughan, B. J., Sereno, M., McGee, S., et al. (2022). The XXL Survey. XLII. The LX − σv relation of galaxy groups and clusters detected in the XXL and GAMA surveys. Monthly Notices of the Royal Astronomical Society, 511(1), 1227-1246. doi:10.1093/mnras/stab3626.

Cite as: https://hdl.handle.net/21.11116/0000-000A-AD86-C
The XXL Survey is the largest homogeneous survey carried out with XMM-Newton. Covering an area of 50deg2, the survey contains several hundred galaxy clusters out to a redshift of ≈2, above an X-ray flux limit of ∼6&nbsp;×&nbsp;10−15 er&nbsp;g cm−2 s−1. The GAMA spectroscopic survey of ∼300 000 galaxies covers ≈286&nbsp;deg2, down to an r-band magnitude of <em>r</em> &lt; 19.8 mag. The region of overlap of these two surveys (covering 14.6&nbsp;deg2) represents an ideal opportunity to study clusters selected via two independent selection criteria. Generating two independently selected samples of clusters, one drawn from XXL (spanning a redshift range 0.05 ≤ <em>z</em> ≤ 0.3) and another from GAMA (0.05 ≤ <em>z</em> ≤ 0.2), both spanning 0.2 ≲ <em>M</em>500 ≲ 5&nbsp;×&nbsp;1014 M, we investigate the relationship between X-ray luminosity and velocity dispersion (<em>LX</em> − σ<em>v</em> relation). Comparing the <em>LX</em> − σ<em>v</em> relation between the X-ray selected and optically selected samples, when not accounting for the X-ray selection, we find that the scatter of the X-ray selected sample is 2.7&nbsp;times higher than the optically selected sample (at the 3.7σ level). Accounting for the X-ray selection to model the <em>LX</em> − σ<em>v</em> relation, we find that the difference in the scatter increases (with the X-ray selected sample having a scatter 3.4&nbsp;times larger than the optically selected sample). Although the scatter of the optically selected sample is lower, we find 13 optically selected GAMA groups undetected in X-rays. Inspection of the difference in magnitude between the first and second brightest galaxies in the cluster, and a stacked X-ray image of these 13 groups, suggests that these are young systems still in the process of forming.