Galactic radio loops Philipp Mertsch with Subir Sarkar The Radio - - PowerPoint PPT Presentation

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Galactic radio loops Philipp Mertsch with Subir Sarkar The Radio - - PowerPoint PPT Presentation

Mar 17, 2024 417 likes •804 views

Galactic radio loops Philipp Mertsch with Subir Sarkar The Radio Synchrotron Background Workshop, University of Richmond 21 July 2017 Foregrounds in B-modes Adam et al. , arXiv:1502.01588 (Planck 2015 results X) Adam et al. , arXiv:1502.01588

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Galactic radio loops

Philipp Mertsch with Subir Sarkar The Radio Synchrotron Background Workshop, University of Richmond 21 July 2017

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Adam et al., arXiv:1502.01588 (Planck 2015 results X)

Foregrounds in B-modes

Adam et al., arXiv:1502.01588 (Planck 2015 results X) Adam et al., 1409.5738 (Planck Int. results XXX)

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Haslam 408 MHz

Haslam et al., A&AS 47 (1982) 1

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… is predominantly synchrotron of CR electrons on the galactic magnetic fields… … and we look at its line-of-sight projections:

The galactic radio background…

wher e and

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Ingredients

CR electrons: • sources: SNRs! pulsars? PWNe? large-scale distribution?!

  • conceptual: stochasticity of sources?
  • propagation: diffusive! convective?

reacceleration? energy losses? Galactic magnetic fields:

  • large-scale, ordered component
  • anisotropic random (also called striated)

component

  • small-scale, turbulent component
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Local e- spectrum and synchrotron

  • require break in IS electron spectrum, e.g. at source:
  • fix local (turbulent) magnetic field:
  • constrain certain propagation models, e.g. disfavour

reacceleration

Strong et al., A&A 534 (2011) A54

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Haslam vs GALPROP

averaging over large parts of the sky…

  • assumes factorisation in

longitude and latitude

  • leads to loss of sensitivity for

structures on intermediate scales

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Difference: Haslam - GALPROP

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1. radio sky: 1. spherical harmonics: 2. angular power spectrum: advantages:

  • information ordered by scale
  • statistically meaningful quantities
  • natural for some applications, e.g. CMB foreground subtraction

Angular power spectrum

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Haslam APS

2 3 1

  • 1. even/odd structure

reflects symmetries of sky map

  • 2. smoother for higher

multipoles

  • 3. power-law

with (Kolmogorov turbulence)

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Smooth component only…

synchrotron: smooth emissivity (GALPROP) free-free: WMAP MEM-template unsubtracted sources: shot noise

Mertsch & Sarkar, JCAP 06 (2013) 041

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Smooth component only…

synchrotron: smooth emissivity (GALPROP) free-free: WMAP MEM-template unsubtracted sources: shot noise

Mertsch & Sarkar, JCAP 06 (2013) 041

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Deficit in RM

1 10 100

  • 2
  • 1

1 2 3 1 10 100 Spherical harmonics l

  • 2
  • 1

1 2 3 Angular Powerspectrum log(Cl / Cl

O12)

Observation O12 Lmax=30pc Lmax=100pc Lmax=300pc Lmax=1kpc Lmax=3kpc

Beck et al., JCAP 05 (2016) 056

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  • plasma perturbations described by

MHD modes, e.g. Alfvén waves

  • two-point correlation function:
  • Fourier transform ➙ power spectrum:
  • bserved in space plasma and

simulations for with (Kolmogorov turbulence)

Turbulence cascade

r

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Scaling the synchrotron emissivity

  • GALPROP assumes a smooth distribution of RMS values for the turbulent

field:

  • can rescale GALPROP’s volume emissivity
  • compute small-scale turbulent field
  • scaling factor
  • exploit scaling of synchrotron emission

with to find:

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Turbulence in projection

Chepurnov, Astron. Astrophys.

  • Transact. 17 (1999) 281
  • consider two-point

correlations on sphere

  • power-law in wavenumber

reflected by power-law in angle (or multipole )

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…including turbulent component

synchrotron: smooth emissivity and turbulence free-free: WMAP MEM-template unsubtracted sources: shot noise

Mertsch & Sarkar, JCAP 06 (2013) 041

power-law in wavenumber reflected by power-law in angle or multipole :

Chepurnov, Astron. Astrophys.

  • Transact. 17 (1999) 281; also:

Cho & Lazarian, ApJ 575 (2002) 63; Regis, Astropart. Phys. 35 (2011) 170

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Radio loops

  • probably shells of old

SNRs

  • can only observe 4

radio loops directly in radio sky

  • total Galactic

population of up to O(1000) can contribute on all scales

Page et al., ApJS 170 (2007) 335

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Radio loops

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Haslam 408 MHz

Haslam et al., A&AS 47 (1982) 1

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Haslam - GALPROP

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Unsharp masked Haslam

Vidal et al., MNRAS 452 (2015) 656

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WMAP9 polarisation

Bennett al., ApJS 208 (2013) 20

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WMAP9 23 GHz polarisation

Page et al., ApJS 170 (2007) 335

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Planck 30 GHz polarisation

Planck collaboration

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assumption: flux from one shell factorises into angular part and frequency part: frequency part : magnetic field gets compressed in SNR shell electrons get betatron accelerated emissivity increased with respect to ISM angular part : assume constant emissivity in thin shell:

Modelling individual shells

Mertsch & Sarkar, JCAP 06 (2013) 041

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assumption: flux from one shell factorises into angular part and frequency part: frequency part : magnetic field gets compressed in SNR shell electrons get betatron accelerated emissivity increased with respect to ISM angular part : assume constant emissivity in thin shell: add up contribution from all shells

Modelling individual shells

Mertsch & Sarkar, JCAP 06 (2013) 041

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…including ensemble of shells

O(1000) shells of old SNRs present in Galaxy we know 4 local shells (Loop I-IV) but others are modeled in MC approach they contribute exactly in the right multipole

Mertsch & Sarkar, JCAP 06 (2013) 041

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Best fit of local shells and ensemble

O(1000) shells of old SNRs present in Galaxy we know 4 local shells (Loop I-IV) but others are modeled in MC approach they contribute exactly in the right multipole

Mertsch & Sarkar, JCAP 06 (2013) 041

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Anomalies in ILC9 (l≤20)

Liu, Mertsch & Sarkar, ApJL 789 (2014) 29

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Mean temperature

  • WMAP 9yr ILC map
  • smoothing to l ≤ lmax = 20
  • 4° wide band around Loop I (Berkhuijsen et al., 1971)
  • compute <T>
  • p-values from 104 simulations with WMAP 9yr best-fit APS

p-value: 0.01 (ILC9 and SMICA)

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Clustering analysis

  • 20° wide band around Loop
  • distance modulus map: Gj=|arccos(nj . nctr)-radius|
  • Pearson’s correlation coefficient:
  • p-values from 104 simulations with WMAP 9yr best-fit power spectrum

p-value: 4 × 10-4 (ILC9) … 1 × 10-3 (SMICA)

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  • spatially correlates with Loop I
  • unlikely synchrotron (checked with our synchrotron model)
  • frequency dependence:

1. ILC method efficiently suppresses power laws in frequency:

  • ver most of the sky:

in the Loop I region 2. pixelwise correlation between WMAP W- and V-bands with ICL9:

What do we know about anomaly?

Liu, PM & Sarkar, ApJL 789 (2014) 29

synch free-free thermal dust

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Magnetic dipole radiation

Draine & Lazarian, ApJ 508 (1998) 157, ibid., ApJ 512 (1999) 740 Draine & Hensley, ApJ 765 (2013) 169

close to black body, i.e. what is assumed to uniquely define CMB!

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Magnetised dust in SMC

Draine & Hensley, ApJ 757 (2012) 103

thermal dust typical spinning dust low- foreground magnetic dust very flat spectra, ; dependence on compound, grain size, shape…

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Summary

1. Lack of angular power in the Galactic radio background for ℓ=10…100 2. Small-scale turbulence cannot explain it 3. A population of O(1000) shells from

  • ld supernova remnants provides the

angular power needed 4. Excess in CMB map. Magnetised dust?