Revealing hidden structures in the Zone of Avoidance -- a blind MeerKAT HI Survey of the Vela Supercluster

Abstract: We conducted the MeerKAT Vela Supercluster survey, named Vela$-$HI, to bridge the gap between the Vela SARAO MeerKAT Galactic Plane Survey (Vela$-$SMGPS, $-2^{\circ} \leq b \leq 1<sup>{\circ}$), and optical and near-infrared spectroscopic observations of the Vela Supercluster (hereafter Vela$-$OPT/NIR) at $|b| \gtrsim 7<sup>{\circ}$. Covering coordinates from $$263^{\circ} \leq \ell \leq 284<sup>{\circ}$$ and $1^{\circ} \leq b \leq 6.2<sup>{\circ}$ above, and $-6.7^{\circ} \leq b \leq -2<sup>{\circ}$ below the Galactic Plane (GP), we sampled 667 fields spread across an area of ${\sim} \rm 242 ~deg<sup>2$. With a beam size of ${\sim} 38&#39;&#39; \times 31&#39;&#39;$, Vela$-$HI achieved a sensitivity of $\langle \rm rms \rangle = 0.74$ mJy beam$<sup>{-1}$ at 44.3 km s$<sup>{-1}$ velocity resolution over ${\sim}$67 hours of observations. We cataloged 719 galaxies, with only 211 (29%) previously documented in the literature, primarily through the HIZOA, 2MASX, and WISE databases. Among these known galaxies, only 66 had optical spectroscopic redshift information. We found marginal differences of less than one channel resolution for all galaxies in common between HIZOA and Vela$-$SMGPS, and a mean difference of $70 \pm 15$ km s$<sup>{-1}$ between optical and HI velocities. Combining data from Vela$-$SMGPS, Vela$-$HI, and Vela$-$OPT/NIR confirmed the connection of the Hydra/Antlia filament across the GP and revealed a previously unknown diagonal wall at a heliocentric velocity range of $6500-8000$ km s$<sup>{-1}$. Vela$-$HI reinforces the connection between the first wall at $18500-20000$ km s$<sup>{-1}$ and the inner ZOA. The second wall seems to traverse the GP at $$270^{\circ} \leq \ell \leq 279<sup>{\circ}$$, where it appears that both walls intersect, jointly covering the velocity range $18500-21500$ km s$<sup>{-1}$.