The Vela Supercluster - Rutgers University
Transcript of The Vela Supercluster - Rutgers University
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)
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°)
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
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)
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
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
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
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?
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
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
Justin Jonas (March 2015)
Actual measurement on M63
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
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:
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:
● 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