The Hydrogen Intensity and Real-time Analysis eXperiment

Heiko Heilgendorff

for the HIRAX Collaboration

Big bang, inflation

Dark ages

Structure growth

Dark energy domination

Formation of CMB

Cosmic dawn

Reionization

HIRAX

Baryon Acoustic Oscillations

Image: SDSS

BAOs are fluctuations in the density of baryonic matter

Remnants of primordial sound waves caused by compression and rarefaction of primordial plasma

Sound horizon can be used as a standard ruler to measure the effect of dark energy on expansion

Neutral hydrogen intensity mapping:Very large, low resolution images Combine signal from thousands of galaxies

Measure the characteristic co-moving length scale of BAOs as a function of redshift

Probe the transition to dark energy domination by observing how the universe grew

Investigate a volume, as opposed to a surfaceSDSS DR7

Required Specs for BAO Intensity Mapping

Maximize sensitivity on scales of interest→ Use compact array geometry

Redshift range of interest: 0.8 < z < 2.5 to capture dark energy domination at z ~ 2

→ Required frequencies: 400 – 800 MHz

BAO 150 Mpc angular scale: 3 – 1.3 degrees at 0.8 < z < 2.5

→ Required baseline lengths: 15 – 60 meters

BAO signal level: ~0.1 mK→ Low system temperature, large collecting

area

HIRAX Instrumental approach:

1024 (32x32) close-packed 6m dishes

Dishes are stationary but can be tilted

Operating frequency: 400 – 800 MHz,equivalent redshift = 0.8 – 2.5

Working closely with CHIME: channelize with FPGA ICE boards, correlation with GPUs

Location: Swartfontein Farm (SKA)

The Hydrogen Intensity and Real-time Analysis eXperiment

Science goals:

Measure baryon acoustic oscillations with HI intensity mapping

Characterize dark energy

Radio transient searches

Pulsar searches

Neutral hydrogen absorbers

Diffuse polarization of the Galaxy

http://www.acru.ukzn.ac.za/~hirax

Complementarity with CHIME

HIRAX dishes | CHIME cylinders - different systematics, larger collecting area

Lower RFI at SKA SA Karoo site

CHIME sees whole (accessible) sky each day | HIRAX can integrate deep on narrow strips

HIRAX observes southern sky

• optical surveys: cross-correlation science and foreground mitigation

• more pulsars in south

CHIME HIRAX

Site DRAO, Canada SKA, South Africa

Telescope Cylinder Array Parabolic Dish Array

Field of View 100o NS, 1o – 2o EW 5o – 10o

Beam Size 0.23o – 0.53o 0.1o – 0.2o

Collecting Area 8000 m2 28,000 m2

Sky Coverage Northern Sky Southern Sky

Location

SKA South Africa Karoo site

Swartfontein, Karoo desert

30°41′18.73″S 21°34′07.98″E

SKA I

HIRAX 128

RFI Quiet Zone

HIRAX Schematic

TXTXRX … RX … RX … RX … RX … RX ...

6m dish,f/D = 0.25 (target)

Active balun dual-pol feed

RFOF transmitter Optical

fiber RFOF receiver

16 ADCs per board

ICE

boa

rd +

cra

teG

PU

co

rr

Channelizer

Back plane

GPUX-engine

RF

fro

nt

end

Corner turn network: data shuffle for 1024 freqs per ADC input

Correlation + accumulation, FT beam forming

8-element prototype at Hartebeeshoek Radio Observatory (outside Johannesburg) for about a year now

Informing design, analysis and systematics

Eight “off-the-shelf” f/0.38 dishes fully instrumented - adding new feeds and RFoF in next few months

Fully functional scaled-down digital backend with single ICE board and GPU correlator

Collected about 6 months worth of data so far

HartRAO 8-Element Prototype

HartRAO Prototype Commissioning

Currently characterising instrumental properties from the data

Poor RFI environment at HartRAO limits high-precision characterisation, analyse narrow subset of full bandwidth

We see fringes! Can fit basic beam and gain models.

Plan to shift prototyping effort to low RFI Karoo site in early 2019

Credit: D CrichtonCredit: D Crichton

HIRAX Dishes

Requirements:

● 6m diameter parabolic reflector● f/d = 0.25● Rigid and stable under wind load● Quick and easy elevation

adjustment● Low cost

Options:

● Metal ● Composite

Current prototypes

are unacceptable

New Dish Options

Metal Option

Company: Rebcon

Status: Ready to deploy

Composite Option

Companies: MMS, NRC

Status: Advanced design

Dish Elevation Adjustment

Dish repointing requirements:

30 deg either side of zenith

Max 3 deg adjustment resolution

Quick and easy (2-3 people, ~ 5

min)

Occasional manual elevation

adjustments to build up sky

coverage

Feeds

HIRAX feed based on CHIME

Dual-pol cloverleaf shaped dipole

Originally tried low-loss teflonpassive feeds, but these were too expensive

Now using active feeds which amplify the measured signal at the feed to minimise noise

Newburgh et al, 2016

Radome Feed can

Spider + feed legs

Spider and feed legs

Mounting and positioning feed

Feed can

Ring choke to circularize beam and reduce cross-talk and ground spillover

Aid in mounting waterproofing

Radome

Environmental protection

New f0.25 prototypes will use central fiberglass column

Still to do at HartRAO

Infrastructure• New site layout• Trenching• Foundations for f/0.25

protoype dishes

Install and test f/0.25 dishes• Photogrammetry• RFoF

Test Feeds• System noise

temperature• Beam characterization

HIRAX dark energy forecasts

HIRAX will make a precise measurement of the matter power spectrum in the BAO regime.

Convert power spectrum BAO constraints into constraints on DV in each redshift bin -constrain the BAO scale at the few percent level out to high redshift with HIRAX-1024

Credit: D CrichtonCredit: D Crichton

Predicted Power Spectrum Measurements Predicted Distance Measure Constraints

Outrigger Arrays

AIMS-Rwanda (Outrigger)

(Outrigger)

(Outrigger)

(Outrigger)

(Outrigger)

(Outrigger)

(Primary Array)

(Prototype Array)

We plan to incorporate

outrigger stations in

addition to the main and

prototype arrays

Outrigger arrays will

consist of 8 elements

Outrigger arrays will

provide very long

baselines to localize FRBs

Contribute to astronomy in

Africa

Upcoming Schedule

• Wrap up HartRAO Prototype:

• Test f/0.25 fibreglass and metal dishes, finalise design

• Finalise new feeds, electronics and RFoF for f/0.25 dish

• Drone beam calibration system

• Start work on outriggers in partner African countries

• 8-element prototype at Losberg (main SKA SA) site by Q2 2019

• Build 128-element pathfinder at Swartfontein (HIRAX site) by Q4 2019

HIRAX