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