Extragalactic Radio Background D J Fixsen U MD/Goddard Space Flight - PowerPoint PPT Presentation

ARCADE And Other Measurements of the Extragalactic Radio Background D J Fixsen U MD/Goddard Space Flight Center

Cosmic Radio Background CMB Energy Density  I  (nW m -2 sr -1 ) 100 CIB COB 1 CXB 10 -2 CGB CRB 10 -4 10 20 10 25 10 7 10 10 10 15 Frequency (Hz)

ARCADE Concept Cosmic Microwave Background Systematics, Not Sensitivity! Galactic • Double-Nulled Design Blackbody Emission Calibrator • Adjust reference load to null antenna signal • Adjust calibrator to null sky signal Cold Helium Gas Pool • Measure small differences about null • Calibrator: Cold and Black Antennas • Absorption  > 0.9999 across band 12 ° FWHM • Adjust temperature to match sky Cryogenic 2.7 Differential • Read temperature from embedded thermometers K Radiometers • Eliminate emission from warm objects • Instrument isothermal with 2.7 K CMB Superfluid • Balloon eliminates atmospheric emission 5000 Liter Liquid Bucket Dewar • Open aperture -- no windows (!) Helium Double-Nulled, Cryogenic, and Isothermal

Cryogenic Radiometers Six frequency bands: 3, 5, 8, 10, 30, 90 GHz Chop between horn and load at 75 Hz Load functions as transfer standard, but is black enough (  >0.999) for absolute reference External calibrator (  >0.99997) nulls any remaining instrument asymmetry and provides absolute temperature scale ARCADE is a thermal experiment, not a radiometric experiment!

External Blackbody Calibrator Radiometric Performance • 298 Absorbing cones • Absorption > 0.99997 with height <  Thermal Performance • LHe tank for thermal isolation • Temperature controlled near 2.7 K • 26 embedded thermometers • Absolute scale verified via  transition

Payload Schematic

Sky-Calibrator Comparison Successful thermal operations • Calibrator brackets sky temp • Instrument nulled to < 0.1 K • 8 sky/calibrator comparisons per band • Stable "transfer standard" Error Budget at 3.15 GHz Effect Uncertainty (mK) Instrument Emission 3.2 Linear instrument model allows Calibrator Gradients 6.7 interpolation of sky temperature Thermometer Calibration 1.0 Atmosphere 0.2 Total 7.5

Binned Sky Temperatures Bin calibrated data by position on the sky 408 MHz Sky Map ARCADE data Subtract Galactic emission to search for extragalactic residual

Low-Frequency Radio Surveys Roger et al 1999 Haslam et al 1981 Maeda et al 1999 Reich & Reich 1986

Galactic vs Extragalactic Emission Problem: Can't Use Frequency Dependence to Separate Galactic From Extragalactic Emission I. Spatial Morphology • Dominant plane-parallel disk • Compare radio emission to Galactic latitude II. Line Emission • Clean tracer of Galactic structure • Compare radio to line emission Look For Extra-Galactic Residual Using Multiple Lines of Sight

Plane-Parallel Model North Galactic hemisphere T ~ csc (b) Latitude b Error Bars x20 ARCADE       T ~ T   Gal G   1 GHz Error Bars x5 T G = 0.499  0.030 K  = -2.56  0.04 Scatter from longitudinal structure dominates uncertainty in fit

Radio/Atomic Line Correlation How Could We Detect Radio Halo? Correlate radio vs line emission! • Line emission associated with Galaxy • Line emission has well-defined zero level • Several full-sky surveys (H  , 21 cm, C+) ARCADE 3.15 GHz Correlate ARCADE vs C+ 158  m line • Well mixed in ISM • Important cooling mechanism • Unaffected by extinction

Radio/C+ Correlation Clear correlation T ~ Sqrt( C+ ) ARCADE 3.15 GHz • Radio emission ~ n and C+ ~ n 2 • Bifurcation suggests 2 components • Spatial localization to synchrotron features Radio/C+ slope Estimated Galactic emission = <  > (I C ) 1/2 C+ Intensity in Selected Region Haslam 408 MHz

Galactic Emission Estimate North Galactic Pole Simple models work well in best regions of the sky     • Two methods agree     T ( ) T   G   1 GHz • Single power-law dependence = 0.498  0.028 K T • Consistent with synchrotron G  = -2.55  0.03

Radio Background Measured Background 6x Brighter Measured Radio Background Than Predicted Integrated Sources Gervasi et al. astro-ph/0803.4138

Galaxy vs Background Galactic Emission Extra-Galactic Emission Model Reference Amplitude Amplitude Index Index Technique Position (K) (K) 0.49  0.10 -2.53  0.07 0.94  0.14 -2.65  0.04 C+ NGP 0.50  0.03 -2.56  0.04 0.88  0.07 -2.65  0.03 csc(b) NGP 0.30  0.05 -2.59  0.06 1.13  0.08 -2.65  0.02 C+ SGP 0.37  0.03 -2.65  0.05 1.06  0.07 -2.65  0.02 csc(b) SGP 0.19  0.13 -2.56  0.12 0.93  0.13 -2.58  0.02 C+ Coldest Mean 1.00  0.04 K Varies by factor 2.5  2 = 6.2 for 4 DOF from patch to patch Galactic part agrees between methods, but varies patch to patch Extra-galactic part agrees over both methods and all patches

Comparisons Among Data Sets Fit for CMB temperature plus radio amplitude & index  2 /DOF Data Set T R (K) Index T 0 (K) 1.17  0.12 -2.597  0.035 2.725  0.001 LF+ARC+COBE 17.5/11 1.10  0.16 -2.620  0.040 2.732  0.005 LF+ARC 15.2/10 1.16  0.38 -2.602  0.065 2.725  0.001 LF+COBE .68/2 1.17  0.14 2.725  0.001 ARC+COBE (-2.60) 16.8/8 1.15  0.50 -2.607  0.07 2.81  0.7 LF .66/1 1.04  0.16 2.732  0.004 ARC (-2.60) 14.4/7 Any combination of independent data sets gives the same answer

New Measurements Control/measure offset Gain 1% or better Measure polarization High frequencies: Liquid Helium load Low frequencies: Phased Array

Potential CRB Measurements Back Frequency Wavelength Diameter Precision Notes Temp 3 GHz 10 cm 2 m 2.8 .6 mK ARCADE, Liq He 1.3 GHz 23 cm 6 m 3.3 5 mK Liquid Helium 610 MHz 49 cm 10 m 6.6 30 mK Liquid Helium 250 MHz 1.2 m 30 m 42 .4 K Liquid Nitrogen 110 MHz 2.7 m 75 m 334 3 K Room Temp 74 MHz 4 m 100 m 935 9 K Astronomy Band 38 MHz 7.9 m 200 m 5300 53 K Astronomy Band 25 MHz 12 m 300 m 16000 160 K Astronomy Band 1% Gain precision

Extragalactic Sky Temperature CMB = 2.729  0.004 K

Extragalactic Sky Temperature What is this?? CMB = 2.729  0.004 K Radio background:  T = 55  7 mK at 3.3 GHz 8  detection of extragalactic background

Observed Radio Background ARCADE by itself can not determine spectrum of background Perform identical analysis for full-sky low-frequency radio surveys 22 MHz (Roger et al. 1999) 45 MHz (Maeda et al 1999, Alvarez et al 1997) 408 MHz (Haslam et al. 1981) 1420 MHz (Reich & Reich 1986) Combined ARCADE + Radio data T CMB = 2.732  0.005 K ARCADE T CMB consistent with COBE = 1.10  0.16 K T R (approaching COBE precision!)  = -2.62  0.04 Radio amplitude set by ARCADE  2 = 15.2 for 10 DOF Radio index set by low-freq surveys

Observed Radio Background ARCADE by itself can not determine spectrum of background Perform identical analysis for full-sky low-frequency radio surveys 22 MHz (Roger et al. 1999) 45 MHz (Maeda et al 1999, Alvarez et al 1997) 408 MHz (Haslam et al. 1981) 1420 MHz (Reich & Reich 1986) Combined ARCADE + Radio data T CMB = 2.732  0.005 K ARCADE T CMB consistent with COBE = 1.10  0.16 K T R (approaching COBE precision!)  = -2.62  0.04 Radio amplitude set by ARCADE  2 = 15.2 for 10 DOF Radio index set by low-freq surveys Observed spectral index inconsistent with signature from reionization (  = -2.1)

Loopholes I: ARCADE Error? Thermal Gradients in External Calibrator Model Thermal Profile in Absorbing Cone Pre-Flight Static Model Thermal gradient from heat flow in absorber Flight 21 thermometers sample actual gradient Thermometers 97% of absorber volume within 10 mK of base Coupling to radiometers set by data, not model ARCADE is hugely over-populated with thermometers!

Cross-Checks Above & Below Data CMB Background Background from Radio Surveys 2.725  0.001 COBE --- COBE 2.732  0.004 1.04  0.16 ARCADE T CMB 2.8  0.7 1.14  0.5 Radio Agreement between ARCADE and independent data sets at higher & lower frequencies rules out gradient error • High freq: Preferentially sample cone tips Background from • Low freq: Sample full absorber volume Radio Surveys Combined ARCADE + COBE + Radio data T CMB = 2.725  0.001 K = 1.17  0.12 K T R  = -2.60  0.04  2 = 17.5 for 11 DOF

Loopholes 2: Error in Galactic Model North Polar Cap Coldest Patch 408 MHz Survey South Polar Cap Multiple cross-checks on background • 2 independent techniques • 3 independent reference lines of sight • Consistent background estimate as foregrounds vary by factor of 3

Multiple Background Estimates 60 Estimates of Radio Background • 10 frequencies • 3 lines of sight • 2 Galaxy models Highly correlated in some "directions" Best-Fit Power-Law Model (including covariance)         T ( ) T R   1 GHz Corrected For Radio Sources Straight Fit To Sky Data T R = 1.17  0.12 K T R = 0.97  0.14 K  = -2.60  0.04  = -2.56  0.04 Consistent Estimate of Radio Background