Radio Diagnostics of Turbulence in the Interstellar & Intergalactic media J. M. Cordes, Cornell University URSI 20 August 2002 Probes of free electrons in the Galaxy and intergalactic medium (integrated measures) Why model n e &  n e (mean and fluctuations) in the Galaxy? Conceptual infrastructure –multiphase components of the ISM –Kolmogorov-like turbulence in ionized components the Galaxy? Modeling methods NE2001 = new release (July 2002) Applications & implications Preliminary results for the intergalactic medium

Why detailed modeling? Distance scale for neutron stars –Neutron star populations –Birth/death rates –Correlations with supernova remnant Turbulence in Galactic plasma Galactic magnetic fields (deconstructing Faraday rotation measures) Interpreting scintillations of sources at cosmological distances (AGNs, GRBs) Baseline model for exploring the intergalactic medium (dispersion & scattering in ISM, IGM)

Integrated Measures DM  ds n e Dispersion Measure EM  ds n e 2 Emission Measure RM  ds n e B  Rotation Measure SM  ds C n 2 Scattering Measure Spectrum = C n 2 q - , q = wavenumber (temporal spectrum not well constrained, relevant velocities ~ 10 km/s)  = 11/3 (Kolmogorov value) Scales ~ 1000 km to > pc

INTERSTELLAR DISPERSION DM =  0 D ds n e (s) Known for ~1200 pulsars DM ~ 2 to 1100 pc cm -3 Variable at ~10 -3 pc cm -3 Variations with d,l,b show obvious Galactic structure

Electron density irregularities exist on scales from ~ 100’s km to ~ pc as approximately a power-law spectrum (~ Kolmogorov) Pulsar velocities >> ISM, observer velocities 500 km/s average (100 to 1700 km/s) Extragalactic sources: ISM, observer velocities determine time scales of scintillation ~ 20 km/s Scattering is `strong’ for frequencies < 2 GHz

Interstellar Scattering Effects Used Angular broadening (seeing) Pulse broadening Diffractive interstellar scintillations (DISS)  d = / l d, l d = diffraction scale  d = scintillation bandwidth => Scattering Measure SM

Pulse broadening Pulse broadening vs DM Angular broadening Diffractive Scintillation Dynamic spectrum Visibility functions:

Pulse broadening (recent Arecibo results, R. Bhat et al)  ~ D  2 /2c  -4 Low DM pulsar, no broadening High DM pulsar with broadening SM = 0.92 (  / D) 5/6 11/3 = scattering measure

Estimated Wavenumber Spectrum for  n e Similar to Armstrong, Rickett & Spangler (1995) Slope ~ -11/3 Spectrum = C n 2 q -  SM = LOS integral of C n 2

DM vs Galactic latitude for different longitude bins SM vs latitude

Independent Pulsar Distances Parallaxes:Pulse timing Interferometry Associations:Supernova remnants Globular clusters HI Absorption:Galactic rotation

Very Long Baseline Array PSR B S. Chatterjee et al. (2001)  = 88.5  0.13 mas/yr  = 0.83  0.13 mas D = 1.2kpc V = 505 km/s

Brisken et al. 2001

NE2001 = New Model Cordes & Lazio 2002 astro-ph July Goal is to model n e (x) and C n 2 (x) in the Galaxy Software to the community (cf web site) Supercedes earlier model (Taylor & Cordes 1993, ApJ) Investigate application spinoffs: –Astronomical: scattering degradation of pulsar surveys Imaging surveys at low frequencies (LOFAR, SKA) SETI –Astrophysical: Physics of interstellar turbulence Connection to magnetic fluctuations & CR propagation (scales probed match CR gyroradii over wide energy range)

NE2001 = New Model Cordes & Lazio 2002 astro-ph July Input data {DM, EM, SM, [D L, D U ] = distance ranges} Prior input: –Galactic structure, HII regions, spiral-arm loci –Multi- constraints on local ISM (H , NaI, X-ray) Figures of merit: –N > = number of objects with DM > DM  (model) (minimize) –N hits = number of LOS where predicted = measured distance: d(model)  [D L, D U ] (maximize) –L = likelihood function for distances & scattering (maximize) Basic procedure: get distances right first, then get scattering (turbulence) parameters

NE2001 = New Model Cordes & Lazio 2002 astro-ph July x2 more lines of sight (D,DM,SM) [114 with D/DM, 471 with SM/D or DM] (excludes Parkes MB obj.) Local ISM component (new) (new VLBI parallaxes) [12 parameters] Thin & thick disk components (as in TC93) [8 parameters] Spiral arms (revised from TC93) [21 parameters] Galactic center component (new) [3 parameters] (+auxiliary VLA/VLBA data ; Lazio & Cordes 1998) Individual clumps/voids of enhanced dDM/dSM (new) [3 parameters x 20 LOS] Improved fitting method (iterative likelihood analysis) penalty if distance or SM is not predicted to within the errors

NE2001 Spiral Arms Electron density (log gray scale to enhance local ISM)

Local ISM components & results

Selected Applications Galactic turbulence anisotropy of fluctuations relation to  B and CR prop’n expect correlations of  -ray emission & scattering (GLAST needed) IGM in local group M33 giant pulses from Crab-like pulsars  DM,SM IGM on cosmological scales scattering/scint’n of AGNs by intervening galaxies, Ly  clouds, turbulence in cluster gas, HII regions at EOR GRB & IDV scintillations source sizes vs. t ambient medium IGM

Spatial fluctuations in n e recall dSM = C n 2 ds  F n e 2 ds  F n e dDM F = “fluctuation parameter” varies widely over Galaxy F  (  n e / n e ) 2 / f (outer scale) 2/3 (f = volume filling factor of ionized cloudlets) F varies by >100 between outer/inner Galaxy  change in ISM porosity due to change in star formation rate (?) outer scale ~ 0.01 pc in HII shells, GC > 1 pc in tenuous thin disk estimate:  n e / n e ~ 1

dSM  F n e dDM F  (  n e / n e ) 2 / f (outer scale) 2/3 small F large F Evidence for variations in turbulence properties between inner & outer Galaxy

Constraints on IGM Scattering (work in progress with J. Lazio) Apparent scattering excess over Galactic scattering for some high-z objects Strong upper bounds on source size ‘seen’ by ISM for IDV sources that display RISS at ~5 GHz Ionized IGM contains most of baryons in the Universe:  m   b ~ To satisfy observations, need scattering regions more numerous than L* galaxies.

Scattering of high z AGNs: Interstellar + Intergalactic ? -2.2 Lazio et al. (unpublished)

Summary / Future 1500 lines of sight Reasonably detailed modeling of the Galaxy Galaxy contains significant, unsampled structures on large and small scales VLBI astrometry  parallaxes on ~100 LOS in next few years Pulsar surveys will yield > 2000 pulsars (Arecibo MB) and ~ 10 4 pulsars (SKA)  definition of spiral arms complete sampling of significant HII regions Scattering may yield a unique probe of the ionized IGM

H  Images of Pulsar Bow Shocks Guitar Nebula (1600 km/s) MSP J (100 km/s)

Modeling the Galactic n e &  n e mean & fluctuations are modelled dSM = C n 2 ds  F n e 2 ds  F n e dDM F = “fluctuation parameter” varies widely over Galaxy  n e ~ C n (outer scale) 1/3 outer scale ~ 0.01 to > 1 pc estimate:  n e / n e ~ 1

Distance prediction on large scales