Discovery of a supercluster in the Zone of Avoidance in Vela

Abstract

We report the discovery of a potentially major supercluster that extends across the Galactic plane in the constellation of Vela, at a mean recessional velocity of ∼18 000 km s⁻¹. Recent multiobject spectroscopic observations of this Vela supercluster (VSCL), using AAOmega+2dF and the Southern African Large Telescope, confirm an extended galaxy overdensity in the Zone of Avoidance (ZOA) located where residual bulk flows predict a considerable mass excess. We present a preliminary analysis of ∼4500 new spectroscopic galaxy redshifts obtained in the ZOA centred on the Vela region ($$l = 272{^{\circ}_{.}}5 \pm 20^\circ , b = 0^\circ \pm 10^\circ$$). The presently sparsely sampled data set traces an overdensity that covers $$25^\circ$$ in Galactic longitude on either side of the Galactic plane, suggesting an extent of 25 × 20 deg², corresponding to ∼ 115 × 90 h₇₀ Mpc at the supercluster redshift. In redshift space, the overdensity appears to consist of two merging wall-like structures, interspersed with clusters and groups. Both the velocity histogram and the morphology of the multibranching wall structure are consistent with a supercluster classification. $$K_{\rm s}^{\rm o}$$ galaxy counts show an enhancement of ∼1.2 over the survey area for galaxies brighter than $$M_{K}^{\ast }$$ at the VSCL distance, and a galaxy overdensity of δ = 0.50–0.77 within a photometric redshift shell around the VSCL, when compared with various Two Micron All-Sky Survey samples. Taking account of selection effects, the VSCL is estimated to contribute $$v_\mathrm{LG} \gtrsim 50$$ km s⁻¹ to the motion of the Local Group.

techniques: spectroscopic, surveys, galaxies: clusters: general, galaxies: distances and redshifts, cosmology: observations, large-scale structure of Universe