the vela supercluster - rutgers university
TRANSCRIPT
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The Vela Supercluster: showcasing the need
for deep “whole-sky” HI-surveys
8th PHISCC meeting Rutgers, March 2015
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)
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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)
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à SALT & AAOmega observations of optically and 2M galaxies to map extent of overdensity (l,b) = 240° – 290°; ± (4°-10°)
2012-2103: à About a dozen fields of prospective cluster cores à Most confirmed as clusters at Vela
overdensity distance
SALT 10m & RSS: 8’ field: N~25
AT 4m & AAOmega: 2° field; N ~400
2014: 6 nights in February: à 4300 redshifts in 25 AAOmega fields:
overdensity extends over vast region
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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)
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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)
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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
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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)
Where extinction reaches ~AB = 2mag à hard to get redshifts, even for 2MASX galaxies à Area of ~|b| < ±5-7° unsampled
Mass
Massive overdensity traced over (Δl, Δb) ~ 20° x 20° Assume continuity At 18-22000 km/s à70 x 70 Mpc/h
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Preliminary results from 1 - 6 Feb 2014 AAOmega Observing run: 25 x 2-deg fields observed à N ~ 4300 redshifts
- 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
Comparison to Shapley Supercluster Concentration
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Tully et al 2014, Nature, Laniakea
Although very sparse data at higher redshifts, strong flow lines downwards from Shapley, then bending to left Lepus???? Vela SCL
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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
Only the forthcoming whole-sky HI-surveys WALLABY & WNSHS will provide full census
How much remains hidden behind ZOA? Does the Milky Way hide further surprises?
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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
0 – 10000; 10-16000; 16-2400; black: 24-50000
285 280 275 270 265 260 255 250 245-15
-10
-5
0
5
10
15
285 280 275 270 265 260 255 250 245-15
-10
-5
0
5
10
15
Galactic longitude
Survey area of about
(l x b) = 20° x 12.5°
To trace Vela SCL across ZOA
Goal: Map all galaxies MHI > 9.5 M¤with 16-24000km/s
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MeerKAT Commissioning survey scenario à with Ed Elson
Simulations based on : - 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 ☐°
Updated MeerKAT Specifications:
�s =2kTsys
Ae⌘(�t�⌫)1/2
Survey input parameters:
- channel width Δv = 10 km/s - Baseline 8km (à 15” resolution) - 5σ detection limit
à rms = 3.86 mJy à 0.5 hr
Tsys = 22.4 K; Ae/Tsys ~ 430m2/K; SS = 7.3 x JVLA
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Justin Jonas (March 2015)
Actual measurement on M63
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MeerKAT Commissioning survey scenario à with Ed Elson
Simulations based on : - 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 ☐°
Updated MeerKAT Specifications:
�s =2kTsys
Ae⌘(�t�⌫)1/2
Survey input parameters:
- channel width Δv = 10 km/s - Baseline 8km (à 15” resolution) - 5σ detection limit:
- FOV: 0.85☐° per pointing
Tsys = 22.4 K; Ae/Tsys ~ 430m2/K; SS = 7.3 x JVLA
à rms = 3.86 mJy à 0.5 hr
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Results: Predictions for MeerKAT survey scenario à with Ed Elson
All > 5-σ lg MHI > 9.5 18360 2586 577
All > 5-σ lg MHI > 9.5 8681 527 247
MeerKAT FOV: 0.85 ☐° à to reach goal 250☐° à 106 hrs with M64 à 424 hrs with M32
For Vhel < 24000 km/s:
For 16000 < Vhel < 24000 km/s:
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Results: Predictions for MeerKAT survey scenario à with Ed Elson
All > 5-σ lg MHI > 9.5 18360 2586 577 91800 12930 2885
All > 5-σ lg MHI > 9.5 8681 527 247 43405 2635 1235
MeerKAT FOV: 0.85 ☐° à to reach goal 250☐° à 106 hrs with M64 à 424 hrs with M32
For Vhel < 24000 km/s:
For 16000 < Vhel < 24000 km/s:
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● 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
Conclusions
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