eROSITA spectro-imaging analysis of the Abell 3408 galaxy cluster

• Published in: Astronomy and astrophysics (Berlin) 2022-05, Vol.661, p.A26
• Main Authors: Iljenkarevic, J., Reiprich, T. H., Pacaud, F., Veronica, A., Whelan, B., Aschersleben, J., Migkas, K., Bulbul, E., Sanders, J. S., Ramos-Ceja, M. E., Liu, T., Ghirardini, V., Liu, A., Boller, Th
• Format: Article
• Language: English
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202141411

Context. The X-ray telescope eROSITA on board the newly launched Spectrum-Roentgen-Gamma (SRG) mission serendipitously observed the galaxy cluster Abell 3408 (A3408) during the performance verification observation of the active galactic nucleus 1H 0707–495. The field of view of eROSITA is one degree, which allowed us to trace the intriguing elongated morphology of the nearby ( z = 0.0420) A3408 cluster. Despite its brightness ( F 500 ≈ 7 × 10 −12 ergs s −1 cm −2 ) and large extent ( r 200 ≈ 21'), it has not been observed by any modern X-ray observatory in over 20 yr. A neighboring cluster in the NW direction, A3407 ( r 200 ≈ 18', z = 0.0428), appears to be close at least in projection (~1.7 Mpc). This cluster pair might be in a pre- or post-merger state. Aims. We aim to determine the detailed thermodynamical properties of this special cluster system for the first time. Furthermore, we aim to determine which of the previously suggested merger scenarios (pre- or post-merger) is preferred. Methods. We performed a detailed X-ray spectro-imaging analysis of A3408. We constructed particle-background-subtracted and exposure-corrected images and surface brightness profiles in different sectors. The spectral analysis was performed out to 1.4 r 500 and included normalization, temperature, and metallicity profiles determined from elliptical annuli aligned with the elongation of A3408. Additionally, a temperature map is presented that depicts the distribution of the intracluster medium (ICM) temperature. Furthermore, we make use of data from the ROSAT all-sky survey to estimate some bulk properties of A3408 and A3407, using the growth-curve analysis method and scaling relations. Results. The imaging analysis shows the complex morphology of A3408 with a strong elongation in the SE-NW direction. This is quantified by comparing the surface brightness profiles of the NW, SW, SE, and NE directions, where the NW and SE directions show a significantly higher surface brightness than the other directions. We determine a gas temperature k B r 500 = (2.23 ± 0.09) keV in the range 0.2 r 500 to 0.5 r 500 from the spectral analysis. The temperature profile reveals a hot core within two arcminutes of the emission peak, ${k_{\rm{B}}}T = 3.04_{- 0.25}^{+ 0.29}$ keV. Employing a mass–temperature relation, we obtain M 500 = (9.27 ± 0.75) × 10 13 M ⊙ iteratively. The r 200 of A3407 and A3408 are found to overlap in projection, which makes ongoing interactions plausible. The two-dimension