The Vela Supercluster:
The Vela Supercluster: showcasing the need for deep “whole-sky” HI-surveys Renée C. Kraan-Korteweg ACGC (Astrophysics, Cosmology and Gravity Centre), UCT Michelle Cluver, Tom Jarrett, Maciej Bilicki, Matthew Colless, Ahmed Elagali & Ed Elson Ø Discovery of major supercluster hidden by ZOA Ø Implications Ø Whole sky-surveys and the ZOA Ø A Vela SCL MeerKAT survey scenario (with Ed Elson) 8th PHISCC meeting Rutgers, March 2015 Suspicion of existence of massive overdensity in ZOA just beyond boundaries of current surveys 16-22000km/s Follow-up redshift observations of optically detected galaxies in ZOA in Vela (KK et al) With 6dF instrument à SALT & AAOmega proposals to consolidate & map extent of overdensity (with M Cluver, T Jarrett, M Bilicki, M Colless) à SALT & AAOmega observations of optically and 2M galaxies to map extent of overdensity (l,b) = 240° – 290°; ± (4°-10°) SALT 10m & RSS: 8’ field: N~25 2012-2103: à About a dozen fields of prospective cluster cores à Most confirmed as clusters at Vela overdensity distance AT 4m & AAOmega: 2° field; N ~400 2014: 6 nights in February: à 4300 redshifts in 25 AAOmega fields: overdensity extends over vast region Preliminary results from 1 - 6 Feb 2014 AAOmega Observing run: 25 x 2-deg fields observed à N ~ 4300 redshifts Massive overdensity: traced over ~ 20 o/o 25 observed fields - Velocity histogram shows highly significant peak centred at ~18000km/s - just beyond boundaries of current surveys 16-22000km/s - Overdensity equally prominent above an below optical ZOA - Numerous clusters at 18-20000km/s - Embedded in broader wall-like structure (16-24000km/s) Preliminary results from 1 - 6 Feb 2014 AAOmega Observing run: 25 x 2-deg fields observed à N ~ 4300 redshifts Massive overdensity: traced over ~ 20 o/o 25 observed fields - Velocity histogram shows highly significant peak centred at ~18000km/s - just beyond boundaries of current surveys 16-22000km/s - Overdensity equally prominent above an below optical ZOA - Numerous clusters at 18-20000km/s - Embedded in broader wall-like structure (16-24000km/s) Preliminary results from 1 - 6 Feb 2014 AAOmega Observing run: 25 x 2-deg fields observed à N ~ 4300 redshifts Numerous clusters at 18-20000km/s Clusters embedded in great wall: à 13 massive clusters; 19 medium clusters/massive groups @ Vela z Embedded in broader wall-like structure (16-24000km/s) Redshift coding: 0 – 10000 km/s; 10-16000 km/s; 16-24000 km/s; 24-50000 km/s (black) Massive overdensity traced over (Δl, Δb) ~ 20° x 20° Assume continuity Mass At 18-22000 km/s à70 x 70 Mpc/h Where extinction reaches ~AB = 2mag à hard to get redshifts, even for 2MASX galaxies à Area of ~|b| < ±5-7° unsampled Preliminary results from 1 - 6 Feb 2014 AAOmega Observing run: 25 x 2-deg fields observed à N ~ 4300 redshifts Comparison to Shapley Supercluster Concentration - Massive overdensity traced over (Δl, Δb) >~ 20° x 20° - Is on par with Shapley SSC (Proust et al 2006, N ~ 8600); [also Horologium/Reticulum SCL (Fleenor et al 2006)] - Despite f ~ 1.3 more distant à more extended on the sky: 12° x 30° ßà ~ 20° x 20° 30 x 75 ßà 70 x 70 Mpc/h - Munoz & Loeb 2008: Based on X-ray of clusters in sky: SSC exerts about 9% acceleration on LG - ADD Vela SCL à Although very sparse data at higher redshifts, strong flow lines downwards from Shapley, then bending to left Lepus???? Vela SCL Tully et al 2014, Nature, Laniakea What does it all signify? ● ● ● ● ● Clear evidence for massive SCL in Vela; Vela SCL likely on par with SSC Forms Big Circle of SCL’s across the sky: Vela SCL à Shapley SCL à Ara/Triangulum? It’s impact on bulk flow is significant? – But difficult to assess properly with sparse sampling If it extends across the ZOA it will be even more massive How much remains hidden behind ZOA? Does the Milky Way hide further surprises? Only the forthcoming whole-sky HI-surveys WALLABY & WNSHS will provide full census MeerKAT Commissioning survey scenario à with Ed Elson Ø “only” 25 AAOmega fields, with some other ZOA data à sparsely sampled Ø AB = 2mag à hard to get optical redshifts àArea of ~|b| < ±5-7° unsampled 15 0 – 10000; 10-16000; 16-2400; black: 24-50000 10 5 Survey area of about (l x b) = 20° x 12.5° 0 To trace Vela SCL across ZOA -5 -10 Goal: Map all galaxies MHI > 9.5 M¤with 16-24000km/s -15 285 280 275 270 265 Galactic longitude 260 255 250 245 MeerKAT Commissioning survey scenario à with Ed Elson Updated MeerKAT Specifications: Tsys = 22.4 K; Ae/Tsys ~ 430m2/K; SS = 7.3 x JVLA Simulations based on : Survey input parameters: - Duffy et al 2012 simulations of stellar and HI-content of galaxies (Wallaby & Dingo) - of 4 million galaxies - within z < 0.44 - over FOV of 50 ☐° - channel width Δv = 10 km/s - Baseline 8km (à 15” resolution) - 5σ detection limit s = à rms = 3.86 mJy à 0.5 hr 2kTsys Ae ⌘( t ⌫)1/2 Actual measurement on M63 Justin Jonas (March 2015) MeerKAT Commissioning survey scenario à with Ed Elson Updated MeerKAT Specifications: Tsys = 22.4 K; Ae/Tsys ~ 430m2/K; SS = 7.3 x JVLA Simulations based on : Survey input parameters: - Duffy et al 2012 simulations of stellar and HI-content of galaxies (ASKAP: Wallaby & Dingo) - of 4 million galaxies - within z < 0.44 - over FOV of 50 ☐° - channel width Δv = 10 km/s - Baseline 8km (à 15” resolution) - 5σ detection limit: s = à rms = 3.86 mJy à 0.5 hr - FOV: 0.85☐° per pointing 2kTsys Ae ⌘( t ⌫)1/2 Results: Predictions for MeerKAT survey scenario à with Ed Elson For Vhel < 24000 km/s: All 18360 > 5-σ 2586 lg MHI > 9.5 577 For 16000 < Vhel < 24000 km/s: All 8681 > 5-σ 527 lg MHI > 9.5 247 MeerKAT FOV: 0.85 ☐° à to reach goal 250☐° à 106 hrs with M64 à 424 hrs with M32 Results: Predictions for MeerKAT survey scenario à with Ed Elson For Vhel < 24000 km/s: All > 5-σ lg MHI > 9.5 18360 91800 2586 12930 577 2885 For 16000 < Vhel < 24000 km/s: All > 5-σ lg MHI > 9.5 8681 43405 527 2635 247 1235 MeerKAT FOV: 0.85 ☐° à to reach goal 250☐° à 106 hrs with M64 à 424 hrs with M32 Conclusions ● The case of the Vela SCL … and other new structures… showcase the importance of the forthcoming à “whole-sky” HI survey Wallaby & WNHSH (shallow) with ASKAP & AperTIF ● Deeper whole-sky surveys including ZOA are key in resolving the controversies around bulkflows § - what is amplitude of Bulk Flows on largest scales? - what is their convergence radius? compatible with LCDM? MeerKAT in commissioning time can fill the ZOA gap the bisects the Vela SCL in reasonable time § ● M64 à 106 hrs; M32 à 424 hrs
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