H i galaxy signatures in the SARAO MeerKAT galactic plane survey − III. Unveiling the obscured part of the Vela Supercluster

Abstract

ABSTRACT We conducted a search for $\textrm {H}\, \scriptstyle \mathrm{I}$ emission of the gas-rich galaxies in the Vela region (260° ≤ ℓ ≤ 290°, −2° ≤ b ≤ 1°) to explore the Vela Supercluster (VSCL) at Vhel ∼ 18 000 $\rm km\, s^{-1}$, largely obscured by Galactic dust. Within the mostly Radio Frequency Interference-free band (250 < Vhel < 25 000 $\rm km\, s^{-1}$) of MeerKAT, the analysis focuses on 157 hexagonally distributed pointings extracted from the South African Radio Astronomy Observatory MeerKAT Galactic Plane Survey located in the Vela region (Vela−SMGPS). These were combined into 10 contiguous mosaics, covering an ∼90 square degrees area. Among the 843 $\textrm {H}\, \scriptstyle \mathrm{I}$ detected sources, 39 were previously discovered in the H i Parkes Zone of Avoidance survey (Vhel < 12 000 $\rm km\, s^{-1}$; rms ∼ 6 $\rm mJy\, beam^{-1}$). With the improved rms level of the Vela−SMGPS, i.e. 0.29–0.56 $\rm mJy\, beam^{-1}$, our study unveils nearly 12 times more detections (471 candidates) in that same velocity range. We furthermore could identify 187 galaxy candidates with an $\textrm {H}\, \scriptstyle \mathrm{I}$ mass limit reaching $\log (M_{\rm HI}/\rm {\rm M}_{\odot }) = 9.44$ in the VSCL velocity range Vhel ∼ 19 500 ± 3500 $\rm km\, s^{-1}$. We find indications of two wall-like overdensities that confirm the original suspicion that these walls intersect at low latitudes around longitudes of ℓ ∼ 272°–278°. We also find a strong signature most likely associated with the Hydra/Antlia extension and evidence of a previously unknown narrow filament at Vhel ∼ 12 000 $\rm km\, s^{-1}$. This paper demonstrates the efficiency of systematic $\textrm {H}\, \scriptstyle \mathrm{I}$ surveys with the Square Kilometre Array (SKA) precursor MeerKAT, even in the most obscured part of the Zone of Avoidance.