Revealing hidden structures in the Zone of Avoidance – a blind MeerKAT H <scp>i</scp> Survey of the Vela Supercluster

ABSTRACT We conducted the MeerKAT Vela Supercluster survey, named Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$, to bridge the gap between the Vela SARAO (South African Radio Astronomy Observatory) MeerKAT Galactic Plane Survey (Vela$-$SMGPS, $-2^{\circ } \le b \le 1^{\circ }$), and optical and near-infrared spectroscopic observations of the Vela Supercluster (hereafter Vela$-$OPT/NIR) at $|b| \gtrsim 7^{\circ }$. Covering coordinates from $263^{\circ } \le \ell \le 284^{\circ }$ and $1^{\circ } \le b \le 6.2^{\circ }$ above, and $-6.7^{\circ } \le b \le -2^{\circ }$ below the Galactic Plane (GP), we sampled 667 fields spread across an area of ${\sim } \rm 242 ~deg^2$. With a beam size of ${\sim } 38 \ \mathrm{ arcsec} \times 31 \ \mathrm{ arcsec}$, Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$ achieved a sensitivity of $\langle \rm rms \rangle = 0.74$$\rm mJy\, beam^{-1}$ at 44.3 $\rm km\, s^{-1}$ velocity resolution over ${\sim }$67 h of observations. We catalogued 719 galaxies, with only 211 (29 per cent) previously documented in the literature, primarily through the H i Parkes Zone of Avoidance survey (HIZOA), Two Micron All-sky Survey Extended Source Catalog (2MASX), and Wide-field Infrared Survey Explorer (WISE) data bases. Among these known galaxies, only 66 had optical spectroscopic redshift information. We found marginal differences of less than one channel resolution for all galaxies in common between HIZOA and Vela$-$SMGPS, and a mean difference of $70 \pm 15$$\rm km\, s^{-1}$ between optical and $\textrm {H}\, \scriptstyle \mathrm{I}$ velocities. Combining data from Vela$-$SMGPS, Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$, and Vela$-$OPT/NIR confirmed the connection of the Hydra/Antlia filament across the GP and revealed a previously unknown diagonal wall at a heliocentric velocity range of $6500\!\!-\!\!8000$$\rm km\, s^{-1}$. Vela$-$$\textrm {H}\, \scriptstyle \mathrm{I}$ reinforces the connection between the first wall at $18\,500\!\!-\!\!20\,000$$\rm km\, s^{-1}$ and the inner Zone of Avoidance. The second wall seems to traverse the GP at $270^{\circ } \le \ell \le 279^{\circ }$, where it appears that both walls intersect, jointly covering the velocity range $18\,500\!\!-\!\!21\,500$$\rm km\, s^{-1}$.