Oxford Astrophysics

C-BASS – The C-Band All Sky Survey

Oxford University – Oliver King, Christian Holler, Mike Jones, Angela Taylor, Matthew Brock, Jaya John John, Paul Grimes

– Secondary Optics, Feed, Polarimeter/Receiver, Cryogenics, BackendManchester University – Rod Davies, Richard Davis Clive Dickinson, Tess Jaffe, Paddy Leahy, Stuart Lowe, Neil Roddis, Althea Wilkinson, Peter Wilkinson

– Low Noise AmplifiersCalTech/JPL/OVRO – Dayton Jones, Russ Keeney, Charles Lawrence, Erik Leitch, Stephen Muchovej, Tim Pearson, Tony Readhead, Graça Rocha, Matthew Stevenson

– Northern Survey, OVRO Antenna, Backend and Data AcquisitionRhodes University/HartRAO – Roy Booth, Charles Copley, Justin Jonas

– Southern Survey, MeerKAT Support Site Antenna

Oxford Astrophysics

C-BASS – The C-Band All Sky Survey

• 4.5-5.5 GHz all sky survey of intensity and polarization• 0.85° FWHM maps to 100 µK rms noise per pixel (I, Q and U)• Systematics below 5% of noise• Science goals:

– Survey of diffuse galactic synchrotron emission– Provide synchrotron foreground template for CMB missions– Study galactic magnetic field and interstellar medium

• Instrument:– Combined correlation radiometer and pseudo-correlation polarimeter with

e-Merlin LNAs– Actively controlled 4 K reference loads– Profiled corrugated horn and planar OMT– 6.1m dish at OVRO and 7.1m dish at MeerKAT support site – each with

new shaped 2ndry and absorber tunnel – First receiver – analogue backend for South African site– Second receiver – all-digital backend for OVRO (for RFI excision)– Dedicated RFI monitor at OVRO

Oxford Astrophysics

Receiver and optics

Oxford Astrophysics

Status and Timescales• Both antennas on-site and undergoing commissioning

• 1st receiver, secondary and foam support to be shipped to OVRO Weds/Thurs

– Receiver tested on sky in Oxford – Tsys < 20K, stability good

– Will be tested at OVRO with initial survey before shipping to MeerKAT site • 2nd (digital backend) receiver construction to start soon

– Planned ship date to OVRO – Feb 2010• OVRO commissioning Jul-Sept 2009• Initial Northern survey/testing - Sept 2009-Jan 2010• Southern survey - 1 year from Mar 2010• Northern survey – 1 year from

Sept 2009

• Data release 2011/12

Oxford Astrophysics

Predictions

• I, Q and U maps – Planck sky model• Compare Planck to Planck + C-BASS (Single

pixel, MCMC parameter fits)• Typical high latitude pixel (2° beam):

– Spectral index bias reduced – Stokes I -0.14 to 0.015; Q,U -0.16 to 0.03

– 70 GHz synchrotron amplitude error – Stokes I 0.09 μK to 0.03 μK; Q,U 0.3 μK to 0.045 μK

– 70 GHz synchrotron bias – Stokes I 0.9 μK to 0.15 μK; Q,U 0.015 μK to 0.003 μK

• 5-7 times reduction in synchrotron residuals in CMB band