The Ability of Planck to Measure Unresolved Sources

Bruce PartridgeHaverford College

For the Planck Consortium

Outline

Properties of Planck and the missionCalibration of PlanckPlanck observations of point sources and the PCCS

Properties of the Planck MissionLaunch 14 May 2009-- still observing at 30, 44 and 70 GHz (LFI)-- High Frequency (HFI) observations ended Jan. 2012

One sky survey every 6 months

Properties of the Planck MissionIn solar orbit at L2

Spin axis anti-parallel Earth & Sun

Properties of the Planck Mission: Scan Strategy

Satellite spins at 1 Hz

Spin axis kept anti-parallelEarth-Sun direction

Optical axis at ~85o

Resulting sky coverage in Galactic coordinates:

Sky surveyed every~6 months

PlanckSingle 2.3 m primary mirror

(shielded); oversize secondary74 detectors (HEMTs and

bolometers) with individual feed horns

Detectors (and some optics) actively cooled

Planck Frequencies

Frequencies chosen for primary mission – mapping the CMB-- 3 “cosmology bands”: 70, 100, 143 GHz-- two lower frequencies for synchrotron foregrounds: 30 & 44 GHz-- higher frequencies for thermal dust emission: 217, 353, 545 & 857

GHz

Galaxy spectrum (Arp 220)

Note substantial bandwidths CMB frequency

sweet spot

Planck Calibration

Currently based on “cosmic dipole” -- Doppler effect induced by solar motion, as measured by WMAP: ΔT/T = v/c

Will soon be based on yearly orbital motionWhich is absolute

Need for care in accounting for sidelobes, subtracting Galactic emission, etc . – therefore iterate (see Planck 2013 Results, V)

Estimates of Absolute Accuracy of Calibration

For LFI (30, 44 and 70 GHz), preliminary new work shows consistency and accuracy at ~0.3 % (0.6% cited in Planck 2013 Results, II)

Still preliminary

Transfer of Calibration to Compact Sources

Two issues:

1. Color correction

2. Role of beam solid angle

Transfer of Calibration to Compact Sources

Color correction (needed because of large bandwidth)

Dipole calibration is on CMB thermal spectrum; radio source spectraquite different

Color correction depends on spectral index: for = -2 to +1, magnitude < 5% for frequencies to 217 GHz

Transfer of Calibration to Compact SourcesRole of beam solid angle: Flux density S ∞ Tmeasinst

So inst must be known

schematic Determined in flight from planetobservations; extended by physicaloptics calculations

Varies slightly over sky (calculated for each sky position by FEBeCop)

Approx. figures: 30 GHz 33.16 arcmin 44 GHz 2 beams = 30.55; the third = 23.17 70 GHz 13.08

100 GHz 9.47 143 GHz 7.14 217 GHz 4.9

The Planck Catalogue of Compact Sources (PCCS)

Nine lists of sources, one for each frequencyReliability > 80% Completeness depends on flux density (and Galactic latitude)Flux densities use correct beams; not color-corrected……and are averaged over 15 months

Catalogues available at ESA Planck Legacy Archive: http://pla.esac.esa.int/pla/pla.jnlp

Errors from receiver noise and CMB background (CMB-subtracted maps will later be available)

At low S, subject to flux boosting (“Eddington bias”)

Internal Validation of PCCS

Compare measured flux densities in a band to those interpolated from two neighboring bands:

E.g., compare measured (and color-corrected) flux at 70 GHz to that interpolated from 44 and 100 GHz values

Measured flux is consistent or (slightly) higher -- if we allow for spectral curvature, Planck flux densities at 30 -353 GHz are all consistent at few percent level or better

External Comparisons of PCCS

See poster by Ben Walter and me.

Can Planck’s absolute calibration be carried over to ground-based instruments?

For bright, compact sources at high Galactic latitude, Planck calibration is accurate, unbiased and absolute

Crucial remaining issue: variabilityat least up to 217 GHz, where Planck counts are dominated by

blazars

Mitigate by observing many sources and by trying to make ground-based observations coincide with Planck’s

External Comparisons of PCCSOne example: compare Planck measurements at 28.4 GHz and 44.1

GHz with JVLA observations at 28.45 and 43.34 GHz (project with Rick Perley and Brian Butler of NRAO)

Scatter due to variability: we await ~simultaneous Planck observations.

0 1 2 3 4 5 6 7 8 9 100

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4

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10f(x) = 0.977636724218368 xR² = 0.87907344969733

VLA FLux

Plan

ck F

lux

External Comparisons of PCCSAnother example: Planck compared to Atacama Cosmology

Telescope at ~148 GHz

Scatter still due to variability – so dropEvidently variable sources one by one:

Using Planck to Calibrate Ground-Based Radio Telescopes

Simultaneous observations of many bright, compact sources should allow ~1% absolute calibration of ground- (and space-) based instruments at 30-217 GHz

JVLA and ATCA observations undertaken in May for this purpose

Calibration depends on exact (<1%) knowledge of solid angle of Planck beams

Current estimates of accuracy a few 1/10 %

(more details in poster by Ben Walter)

Using Planck to Calibrate Planetary Temperatures

Use absolutely calibrated CMB instruments to refine measurements of planetary brightness temperatures:--

Newly proposed (Perley and Butler, ApJS 2013) flux density scale is based on Mars brightness temperatures (Rudy et al., Icarus, 1987) as fine-tuned by WMAP( Weiland et al., ApJS 2011)

Higher resolution CMB instruments (SPT and ACT) can extend to other planets, e.g. Uranus

Using Planck to Calibrate Planetary Temperatures

Use absolutely calibrated CMB instruments to refine measurements of planetary brightness temperatures:--

Process just getting started; we await new and better Jupiter measurements from Planck, and Uranus from SPT and ACT

Again, ~1% precision should be possible

An Example: Measurements of Brightness Temperature of Jupiter

Current situation:

From Planck 2013 paper V:consistency to< 1-2%

WMAP and Planck Measurements of Jupiter

From Planck 2013 Results IV:consistency to< 1-2%

Planck Can Calibrate both Radio Astronomy Fux Density Scales and Planetary Temperatures

A nice side benefit of an instrument designed for mapping CMB

Kiitos…..

And now to answer questions

Effect of stray light

Currently sidelobes calculated at one (central) frequency for each band – total effect of far sidelobes ~0.4%Now calculating sidelobes for proper bandpasses – likely to increase slightly (to ~0.6%??)

Comparison with WMAP -- they use symmetrized beam, uniform over skyOK at ecliptic poles; not as good an approximation in ecliptic plane(we use proper FEBeCop beams)