The SRG/eROSITA All-Sky Survey: Large-scale view of the Centaurus cluster
Authors: Veronica Angie , Reiprich Thomas H. , Pacaud Florian , Sanders Jeremy S. , Gattuzz Efrain , Yeung Michael C. H. , Bulbul Esra , Ghirardini Vittorio , Liu Ang , Mannes Caroline , Morelli Alexander , Ota Naomi 
Published: January 2025

Context. The Centaurus cluster is one of the brightest and closest clusters. Previous comprehensive studies were done only in its brightest part (r < 30′), where the centers of the main substructures (Cen 30 and Cen 45) are located, and only a small fraction of the outskirts has been studied.

Aims. Through this work, we aim to characterize the intracluster medium (ICM) morphology and properties of the Centaurus cluster out to the radius within which the density is 200 times the critical density of the Universe at the redshift of the cluster, R200 (91′).

Methods. We utilized the combined five SRG/eROSITA All-Sky Survey data (eRASS:5) to perform X-ray imaging and spectral analyses in various directions out to large radii. We employed some image manipulation methods to enhance small- and large-scale features. Surface brightness profiles out to 2R200 were constructed to quantify the features. We acquired the gas temperature, metallicity, and normalization per area profiles out to R200. We compared our results with previous Centaurus studies, cluster outskirts measurements, and simulations. Comprehensive sky background analysis was done across the field of view in particular to assess the variation of the eROSITA Bubble emission that partially contaminates the field.

Results. The processed X-ray images show the known sloshing-induced structures in the core, such as the cool plume, cold fronts, and ram pressure-stripped gas. The spectra in the core (r ≤ 11 kpc) are better described with a two-temperature (2T) model than an isothermal model. With this 2T analysis, we measured a lower temperature from the cooler component (∼1.0 keV) and a higher metallicity (∼1.6 Z⊙), signifying an iron bias. In the intermediate radial range, the temperature peaks at ∼3.6 keV, and we observed prominent surface brightness and normalization per area excesses in the eastern sector (Cen 45 location). Temperature enhancements near the location of Cen 45 imply that the gas is shock-heated due to the interaction with Cen 30. We reveal that the eastern excess emission extends even further out, reaching R500. The peak excess of normalization is located at ∼23′ from the center (8′ behind the center of Cen 45) with a 45% and 7.7σ above the full azimuthal value. This might be the tail or ram pressure-stripped gas from Cen 45. There is a temperature decrease of a factor of about two to three from the peak to the outermost bin at R500 − R200. We find good agreement between the outer temperatures (r > R2500) with the temperature profile from simulations and the temperature fit from Suzaku cluster outskirts measurements. We detect significant surface brightness emission to the sky background level out to R200 with a 3.5σ, followed by 2.9σ at 1.1R200. The metallicity at R500 − R200 is low but within the ranges of other outskirts studies.

Conclusions. We present the first whole azimuth beyond ∼30′ measurement of the ICM morphology and properties of the Centaurus cluster, and increasing the probed volume by a factor of almost 30. While the cluster core is rich in features as a result of active galactic nucleus feedback and sloshing, the cluster outskirts temperature of Centaurus follows the temperature profile of clusters in simulations as well as the temperature fit from other cluster outskirts measurements.