Discovery of an overlapping cluster in the Abell 1674 field with Suzaku

Abstract

Abstract We present the results of a Suzaku observation of Abell 1674, an optically very rich (richness class 3) cluster cataloged as z = 0.1066. We discover the He-like Fe K-shell line from the central region for the first time, and find that the X-ray spectrum yields a high redshift of $0.215^{+0.007}_{-0.006}$. On the other hand, the spectrum of the south-western region is fitted with a redshift of 0.11 ± 0.02 by the He-like Fe L-shell lines, consistent with the optically determined value. The gas temperature, metal abundance, and core radius of the X-ray emission in the central region are 3.8 ± 0.2 keV, 0.20 ± 0.05 Z⊙, and 450 ± 40 kpc, respectively, while those in the south-western region are 2.0 ± 0.2 keV, $0.41^{+0.17}_{-0.13}\,Z$⊙, and $220^{+90}_{-70}$ kpc, respectively. These parameters are typical for clusters. We thus conclude that Abell 1674 consists of two independent clusters, A 1674-C at z ∼ 0.22 and A 1674-SW at z ∼ 0.11, overlapping along the line of sight. The X-ray luminosity of A 1674-C within r = 2 Mpc is (15.9 ± 0.6) × 1043 erg s−1 in the 0.1–2.4 keV energy band, while that for A 1674-SW is (1.25 ± 0.07) × 1043 erg s−1. Both are consistent with those expected from the L–T relation of clusters within a factor of 2. This is another supporting factor for our conclusion.