H i galaxy signatures in the SARAO MeerKAT Galactic Plane Survey - I. Probing the richness of the great attractor wall across the inner zone of avoidance

This paper presents the first H i results extracted from the South African Radio Astronomy Observatory (SARAO) MeerKAT Galactic Plane Survey (SMGPS) - a narrow strip (Δb ∼3°) along the southern Milky Way. The primary goal consisted in tracing the great attractor (GA) wall across the innermost zone of avoidance. We reduced a segment spanning the longitude range 302° 332 for the redshift range z ≤ 0.08. The superb SMGPS sensitivity (rms = 0.3-0.5 mJy beam-1 per 44 km s-1 channel) and angular resolution (∼31″ × 26″) lead to a detection limit of log(MH i/M·) ≥ 8.5 at the GA distance (km s-1). A total of 477 galaxy candidates were identified over the full redshift range. A comparison of the few H i detections with counterparts in the literature (mostly HIZOA) found the H i fluxes and other H i parameters to be highly consistent. The continuation of the GA wall is confirmed through a prominent overdensity of N = 214 detections in the GA distance range. At higher latitudes, the wall moves to higher redshifts, supportive of a possible link with the Ophiuchus cluster located behind the Galactic Bulge. This deep interferometric H i survey demonstrates the power of the SMGPS in improving our insight of large-scale structures at these extremely low latitudes, despite the high obscuration and continuum background.