Sambatriniaina H.A Rajohnson, Renée C. Kraan-Korteweg, Bradley S. Frank, Hao Chen, Sushma Kurapati, Nadia Steyn, D.J. Pisano Department of Astronomy, University of Cape Town, South Africa Contact: aychasam@gmail.com New Eyes on the Zone of Avoidance: what can MeerKAT tell us about the hidden core of the Vela Supercluster? ABSTRACT The Zone of Avoidance (ZOA) partially obscures numerous dynamically important structures in the nearby Universe. Among these structures is the Vela supercluster (VSCL), a massive supercluster recently discovered to extend across the Galactic Plane in the constellation of Vela at cz ~ 18000 km s-1; ~260 h70 Mpc [1]. To trace its walls and inner core, we analyzed HI data from the Galactic Plane Legacy Survey (Vela-SMGPS; |b| < 2º) between 260º < l < 290º, complemented by the full VSCL survey (Vela-HI, |b| < 7º, 262º < l < 284º), both using MeerKAT 64 L-band and 4K correlator out to cz < 25500 km s-1 (z < 0.085). This is the first time such large systematic interferometric observations have been performed across the thickest layer of the Milky Way. ZoA VSCL [1] Kraan-Korteweg R.C. et al. 2017, MNL 466L, 39 [2] Bilicki, M. et al. 2011. ApJ, 741, 31 [3] Erdogdu P. et al. 2006, MNRAS 368, 1515 [4] Hudson M. J. et al. 2004, MNRAS 352, 61 [5] Kocevski D. D., Ebeling H. 2006, ApJ, 645, 1043 [6] Springob C. M., et al., 2014, 2016, MNRAS, 445, 2677, MNRAS, 456, 1886 [7] Said K. et al. 2020, MNRAS.497.1275S [8] Obreschkow D. et al. 2009abc, ApJ, 698, 1467, ApJ 702,1312, ApJ 703, 1890 [9] Staveley-Smith L. et al. 2016, AJ 151. 52 [10] Bock, D. C. -J. et al., 1999, arXiv [11] www.ilifu.ac.za [12] https://github.com/caracal-pipeline/caracal [13] Serra, P. et al., 2015, MNRAS, 448, 1922 [14] Westmeier, T. et al., 2021, MNRAS, 506, 3962 [15] https://cartavis.org/ [16] Lynden-Bell D., 1994, eds, Astronomical Society of the Pacific Conference Series Vol. 67, Unveiling Large- Scale Structures Behind the Milky Way. p. 289 REFERENCES Fig. 1: The 2MASS Redshift Survey (2MRS) ✪The overall bulk flow results (direction, volumes) from systematic redshift and peculiar velocity surveys do not fully explain the inferred dipole from the Cosmic Microwave Background (CMB) [2,3,4,5]. ✪A residual bulk flow velocity of 273 km s-1 seems to arise beyond cz > 16 000 km s-1 from a mass overdensity in the Zone of Avoidance (ZoA; l ~ 270º-330º), close to VSCL [6,7]. ✪The ZoA remains mostly uncharted due to dust obscuration and high stellar density [8]. Only HI systematic surveys can bridge the gap and map the inner ZoA (so far multi-beam single dish surveys such as HIZOA [9] were shallow and affected by continuum at lowest latitudes) Parameters Vela-SMGPS Vela-HI Fields number 157 667 Total track time ~12 hours ~ 8-9 hours Survey area 90 sq. deg (260°< l < 290°, -2° < b < 1°) 247 sq. deg (262° < l < 284°, b < |7°|) Mosaic rms 0.35 +/- 0.07 mJy/beam 0.69 +/- 0.13 mJy/beam BACKGROUND & MOTIVATIONS OBSERVATION DETAILS Goals: Detecting gas-rich spirals with MHI > 4 +/- 0.5 x109 M⨀ along the two merging VSCL walls using the Vela-SMGPS and Vela-HI out to 25 000 km s-1. Fig. 3: Vela-SMGPS and Vela-HI survey configurations toward Vela. Red circles indicate the Vela-SMGPS field configurations, which are combined to form 10 mosaics (T24 to T33) of 22 fields each, providing uniform coverage over 3.5° x 3°. The Nyquist sampled fields are distributed into 8 blocks of observations (black and blue circles) in Vela-HI. The figure is overlaid on the greyscale continuum map from the Sydney University Molonglo Sky Survey (SUMSS) [10]. ✪ Use of SoFiA-2 [13,14] ✪ Two runs with 3.5 and 4𝜎source ﬁnding thresholds ✪ Source verification: ✪ checking unmasked moment maps ✪ visually inspecting the data using the CARTA software [15]. Fig.2: the Vela spectroscopic survey region. The region of high extinctions in the ZoA is indicated by green contours. Magenta and red dots represent galaxies at the VSCL distance. Fig. 4: Sky distributions of the 1569 newly detected obscur