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The Ability of Planck to Measure Unresolved Sources Bruce Partridge Haverford College For the Planck Consortium.

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Presentation on theme: "The Ability of Planck to Measure Unresolved Sources Bruce Partridge Haverford College For the Planck Consortium."— Presentation transcript:

1 The Ability of Planck to Measure Unresolved Sources Bruce Partridge Haverford College For the Planck Consortium

2 Outline Properties of Planck and the mission Calibration of Planck Planck observations of point sources and the PCCS

3 Properties of the Planck Mission Launch 14 May still observing at 30, 44 and 70 GHz (LFI) -- High Frequency (HFI) observations ended Jan One sky survey every 6 months

4 Properties of the Planck Mission In solar orbit at L2 Spin axis anti- parallel Earth & Sun

5 Properties of the Planck Mission: Scan Strategy Satellite spins at 1 Hz Spin axis kept anti-parallel Earth-Sun direction Optical axis at ~85 o Resulting sky coverage in Galactic coordinates: Sky surveyed every ~6 months

6 Planck Single 2.3 m primary mirror (shielded); oversize secondary 74 detectors (HEMTs and bolometers) with individual feed horns Detectors (and some optics) actively cooled

7 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

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

9 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

10 Transfer of Calibration to Compact Sources Two issues: 1.Color correction 2.Role of beam solid angle

11 Transfer of Calibration to Compact Sources Color correction (needed because of large bandwidth) Dipole calibration is on CMB thermal spectrum; radio source spectra quite different Color correction depends on spectral index: for  = -2 to +1, magnitude < 5% for frequencies to 217 GHz

12 Transfer of Calibration to Compact Sources Role of beam solid angle: Flux density S ∞ T meas  inst So  inst must be known schematic  Determined in flight from planet observations; extended by physical optics calculations Varies slightly over sky (calculated for each sky position by FEBeCop) Approx. figures: 30 GHz arcmin 44 GHz 2 beams = 30.55; the third = GHz GHz GHz GHz 4.9

13 The Planck Catalogue of Compact Sources (PCCS) Nine lists of sources, one for each frequency Reliability > 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: Errors from receiver noise and CMB background (CMB-subtracted maps will later be available) At low S, subject to flux boosting (“Eddington bias”)

14 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 GHz are all consistent at few percent level or better

15 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: variability at 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

16 External Comparisons of PCCS One example: compare Planck measurements at 28.4 GHz and 44.1 GHz with JVLA observations at and GHz (project with Rick Perley and Brian Butler of NRAO) Scatter due to variability: we await ~simultaneous Planck observations.

17 External Comparisons of PCCS Another example: Planck compared to Atacama Cosmology Telescope at ~148 GHz Scatter still due to variability – so drop Evidently variable sources one by one:

18 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 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)

19 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

20 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

21 An Example: Measurements of Brightness Temperature of Jupiter Current situation: From Planck 2013 paper V: consistency to < 1-2%

22 WMAP and Planck Measurements of Jupiter From Planck 2013 Results IV: consistency to < 1-2%

23 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

24 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 sky OK at ecliptic poles; not as good an approximation in ecliptic plane (we use proper FEBeCop beams)

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