1. CMB@50 Princeton June 10th, 2015 Challenges and prospects for better intensity spectrum measurements Giorgio Sironi Physics Department University of Milano Bicocca 1

2. CMB@50 Princeton June 10th, 20152 CMB Intensity Spectrum Immediately after the discovery observations were mainly directed to confirm the first order properties of the CMB. Blackbody spectrum and temperature × Uniform spatial distribution × No polarization × by ~ 1990 all of them were confirmed

3. CMB@50 Princeton June 10th, 20153 CMB Intensity Spectrum Almost simultaneously the search for second order effects began and gradually results arrived Dipole anysotropy × Anisotropies × Residual polarization E-modes × B-modes (?) S-Z effect × Spectral distortions ? ! spectral distortions have still to be detected !

4. CMB@50 Princeton June 10th, 20154 CMB Intensity Spectrum Models and observational results on spectral distortions will be presented by other speakers at this same conference. I will simply remark that between ~0.5 GHz and ~500 GHz CMB intensity measurements are consistent with a thermodynamic temperature of the blackbody distribution which best fit the data T th CMB = (2.7260 +/- 0.0013) K (2009 ; revised value of FIRAS original value) No evidence of distortions

5. CMB@50 Princeton June 10th, 20155 CMB Intensity Spectrum Models suggests wide features which can be characterized by Y FF (free-free) μ (chem. pot.,BE spectrum) y (comptonization) ← Examples from Chluba and Sunyaev 2012 and narrow features lines at various frequencies (x=hν/KT= 1.74 10 -2 ν(GHz))

6. CMB@50 Princeton June 10th, 2015 6 Recollection of measurements of CMB thermodynamic temperature Most recent data in red (Old) models: dotted line CMB Intensity Spectrum 66

7. CMB@50 Princeton June 10th, 20157 CMB Intensity Spectrum so far we can only say that there are upper limits to the amplitude of the distortions, ranging from ~10 -3 K at high frequencies to 10 -1 K at low frequencies; upper limits to the distortions parameter 6 10 -6 < Y ff < 1.3 10 -5 |μ BE | < 6 10 -5 |y| < 1.5 10 -5 controversial evidence below ~ 3 GHz ! very far from expectations !

8. CMB@50 Princeton June 10th, 2015 8 CMB is almost everywhere buried in a sea of foregrounds and we can think of three frequency regions where carry on new observations CMB Intensity Spectrum

9. CMB@50 Princeton June 10th, 20159 CMB Intensity Spectrum Region 1 ← 0.3 <ν(GHz)<30 ~ ← 0.1 < (1/λ) cm -1 < 1 ~ ← 0.05 < x < 0.6 past observation method: absolute measurements of temperature at various frequencies, sometime coordinated, from ground sites or balloons detectors: resonant antennae and hetherodyne receivers (partially cooled) contamination: ground and atmospheric emission sky foregrounds: galactic diffuse emission (partially polarized, dominant below 0.6 GHz); unresolved extragalactic sources distortion expected : |ΔT| ≤ few times 10 -5 K better two subregions Region 1/A Region 1/B 0.3 < ν(GHz) < 3 3 < ν(GHz) < 30

10. CMB@50 Princeton June 10th, 201510 CMB Intensity Spectrum Region 2 30 <ν(GHz)<600 ~ 1 < (1/λ) cm -1 < 20 ~ 0.6 < x < 10 past observation method: absolute measurements of temperature - from space (FIRAS) with almost continous frequency coverage - from ground and balloons at selected frequencies - excitation of CN optical lines detectors: concentrators plus bolometers or resonant antennae and hetherodyne receivers (cooled) contamination: ground and atmospheric emission (where applicable) sky foregrounds: residual galactic synchrotron and dust emissions distortion expected : |ΔT| << 10 -6 K

11. CMB@50 Princeton June 10th, 201511 CMB Intensity Spectrum Region 3 600 < ν(GHz)< 3000 → ~ 20 < (1/λ) cm -1 < 100 → ~ 10 < x < 500 → past observation method: absolute measurements of temperature at various frequencies from balloons and in space detectors: bolometers and bandpass filters contamination: vehicle emission (where applicable) sky foregrounds: galactic dust, unresolved extragalactic sources distortion expected : |ΔT| ≤ ?

12. CMB@50 Princeton June 10th, 201512 CMB Intensity Spectrum How to improve observation ? If we represent the radiation spectrum by T(ν) dν = k ν -α(ν) dν we can look for deviation from a flat distribution (α(ν) = 1) getting the spectral index α(ν) ≃ -(ΔT(ν)/Δν)(ν m / T m ) by differential measurements (usually more accurate than absolute measurements)

13. CMB@50 Princeton June 10th, 2015 13 CMB Intensity Spectrum It can be done a)observing simultaneously the same region of sky at two frequencies (absolute measurement of temperature only at few selected frequencies) b)with continous frequency coverage (instead of observations at few, selected frequencies) combined with c)ADC signal conversion as soon as possible (to let us adjust via software the system configuration)

14. CMB@50 Princeton June 10th, 2015 14 CMB Intensity Spectrum Toward better results d)large (~5° ≤ Δθ ≤ ~15 ° ) well shaped beam (no narrow beam required) e)observation of few, properly selected, regions of sky (~ 10 Δθ x 10 Δθ) f)direct measurements of the foregrounds necessary (looking for polarization and position dependence of α(ν) ) f)preferably from space in very quiet regions (L2 ?)

15. CMB@50 Princeton June 10th, 2015 15 CMB Intensity Spectrum Toward better results C = radiation collector (concentrator/parabola) PhDis = phase discrim. S = frequency dispersion (Michelson interf.) PD = power detector (bolometer/diode) MS = mass storage and on board computer T o = reference noise source

16. CMB@50 Princeton June 10th, 2015 16 CMB Intensity Spectrum common layout, different technical implementations at least three different experiments ← 0.3 - 30 GHz : ground / space (parabola↔concentrator, preamps + diodes↔bolometers, R.A. techniques) 30 – 600 GHz : balloons / space (concentrator, bolometers, optical techniques) 100 – 900 → GHz : balloons / rockets / space (concentrator↔optical mirror, bolometers, IR techniques) (possible ovrerlap of the last two regions)

17. CMB@50 Princeton June 10th, 2015 17 CMB Intensity Spectrum BUT space is expensive and there are long waiting lists: newly proposed experiments cannot be expected to fly before 2030 therefore to be practical and keep our feets on the ground Regions 2 and 3: we can decide to be part of more ambitious space and balloon experiments aimed at measuring the CMB polarization (proposal already in the pipeline) Region 1: while planning future space experiments, we can begin testing new technical solutions and making ground observations from special site (Antarctica, Atacama, …)

18. CMB@50 Princeton June 10th, 201518 CMB Intensity Spectrum Past and present proposed experiments we can delegate part of the observation or take advantage of technical studies Region 2 and 3 PIXIE, PRISM, … Region 1 LOBO, DIME ….

19. CMB@50 Princeton June 10th, 201519 The End of presentation not of observation

20. CMB@50 Princeton June 10th, 2015 20 CMB Intensity Spectrum Risultati TRIS

21. CMB@50 Princeton June 10th, 2015 21 CMB Intensity Spectrum Risultati Arcade 2

22. CMB@50 Princeton June 10th, 2015 22 CMB Intensity Spectrum x (cm-1) =3,3 10 -2 ν(GHz)

23. CMB@50 Princeton June 10th, 201523 CMB Intensity Spectrum Glossario bolometer, coherent detector, diode spectrum analyzer, Michelson interferometer ………………….

24. CMB@50 Princeton June 10th, 2015 24 CMB Intensity Spectrum Toward better results C = radiation collector (concentrator/parabola) PhDis = phase discrim. S = frequency dispersion (Michelson interf.) PD = power detector (bolometer/diode) MS = mass storage and on board computer T o = reference noise source