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Intracluster Shocking of the ISM in Virgo Spirals: Modified FIR-Radio Relations. Eric J. Murphy (Caltech). The EVLA: Galaxies Through Cosmic Time. NGC 4254. NGC 4330. NGC 4402. NGC 4501. NGC 4522. NGC 4580. SPITSOV: Spitzer Survey of Virgo.

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intracluster shocking of the ism in virgo spirals modified fir radio relations

Intracluster Shocking of the ISM in Virgo Spirals: Modified FIR-Radio Relations

Eric J. Murphy


The EVLA: Galaxies Through Cosmic Time

spitsov spitzer survey of virgo

NGC 4254

NGC 4330

NGC 4402

NGC 4501

NGC 4522

NGC 4580

SPITSOV: Spitzer Survey of Virgo

Team: J. Kenney, E. Murphy, G. Helou, A. Abramson, I. Wong, J. Howell,

J. Van Gorkom, R. Beck, B. Vollmer , H. Crowl, A. Chung

  • 44 S0/a-Sm Virgo Spirals
  • Located throughout cluster
  • Range of HI & H properties
  • IRAC & MIPS Imaging; x2 SINGS integration

IRAC 3-color images: 3.6m blue; 4.5m green; 5.8 & 8.0m red

c/o Ivy Wong

fir radio correlation how it works well kind of de jong et al 1985 helou et al 1985
FIR – Radio Correlation: How it works… well, kind of(de Jong et al. 1985; Helou et al. 1985)


  • Driven by Massive Star Formation
    • FIR – Dust heated by Massive stars
      • mfp of dust heating UV photons ~100 pc
    • Radio – CRe- accelerated by SNe in B-field
      • CRe- diffuse ~1 kpc
  • Radio image is smoother version of FIR image



σ = .26

(L. Cowie)

Yun, Reddy, & Condon. (2001)

image smearing analysis e g ngc 5194





Image Smearing Analysis: (e.g. NGC 5194)

Residuals between

Radio & Smeared FIR Images

(Murphy et al. 2006a,b)

B: Best-fit Scale-length

Φ: Improvement

(~x2-3 on average)

22cm Map

A: l = 0.0 kpc

B: l = 0.6 kpc

C: l = 3.0 kpc




comparing fir and radio morphologies e g ngc 4402
Comparing FIR and Radio Morphologies: e.g. NGC 4402

MIPS 70 μm

VLA 20 cm

  • Radio affected more than FIR:
  • – CRe-’s which diffuse far away from SF sites/mol. clouds easier to push
  • around by ICM wind
  • Use FIR image to predict radio distribution.

– Characterize ICM strength and direction: FIR/RC ratios sensitive to current RP!

looking for deviations from expected radio morphology
Looking for Deviations from Expected Radio Morphology

NGC 4402

NGC 4254

  • Smooth 70m map to optimally reduce differences w/ radio disk
    • i.e. predicted radio map
  • Create ratio map
    • obs./mod. radio
  • Identify pixels significantly deviant w.r.t. S/N of map & internal dispersion of disk
    • Excess regions
      • Pix > 1.3
    • Deficit regions are detected
      • Pix < 0.50
  • Quantify severity of deficit by defining:

Ratio maps

Deficit regions

radio continuum deficit excess regions
Radio Continuum Deficit/Excess Regions

HI contours overlaid

  • 6/10 galaxies: we detect deficit regions (pix < 0.50)
  •  Each shows additional evidence of ram pressure effect

Radio Deficits located opposite

synchrotron tails & excess regions:

- associated with ICM wind

ngc 4522 a well studied case for ram pressure stripping

Polarized RC

on HI

Evidence of Ongoing


NGC 4522: A well studied case for ram pressure stripping:



ICM wind

(Vollmer et al. 2004)

(Murphy et al. 2008 (arXiv:0812:2922)

Has only 25% of normal HI (HI def =0.6)

HI truncated in disk at 0.3R25

extraplanar HI (40% of total) on only one side of disk

polarized radio continuum a diagnostic of ram pressure

Pol. on HI

NGC 4501

Polarized Radio Continuum: A Diagnostic of Ram Pressure

Pol. + 6cm on Def.





NGC 4402

ICM wind

ICM wind

  • Magnetic field Vectors aligned parallel with ICM-ISM working surface
  • Evidence of polarized ridges arising from ram pressure in a number of galaxies having radio deficit regions (e.g. N4254, N4388; Vollmer et al. 2008)
  • Such studies will benefit significantly from improved EVLA capabilities!
ngc 4522 comparison of rc deficits with spx pol data
NGC 4522: Comparison of RC Deficits with SPX & POL data:

(SPX & POL data from Vollmer et al. 2004)

Flat Spectral Index:


Just Interior to

Deficit Region

High Polarization:

B-field shear/


Deficit region caused by ICM ram pressure (consistent for other galaxies).

    • CR electrons being re-accelerated by ICM driven shocklets:
    • B-field compressed and sheared:
  • - moderate local RC enhancement; shear stretches B-field resulting in tails.

Moderate RC


deficit vs time since peak pressure
Deficit vs. Time Since Peak Pressure

(Large deficit)

  • tquench:

Time since peak pressure from stellar population studies of Crowl & Kenney 2008.

    • Agree with gas stripping simulation of Vollmer et al.
    • 100 - 300 Myr
      • x5 decrease in peak Pram
      • Similar change in radio deficit region!

(Small deficit)

  • Deficit region is a good indicator of the strength of the CURRENT ram pressure!
severity of deficit vs q
Severity of Deficit vs. q


Low q

High q

  • q’s generally low compared to field galaxies (x2 – 3 )
    • Miller & Owen (2001)
    • Reddy & Yun (2004)
  • q sensitive to strength of ICM pressure?

q ~ log(FIR/Radio)

  • Galaxies with large LOCAL radio deficits have GLOBAL radio enhancements relative to the FIR!
excess radio cr reacceleration by icm shocks
Excess Radio: CR Reacceleration by ICM Shocks?

RC deficit on 6cm RC and B-field Vectors

  • ICM driven shocks:
    • Compress & Shear B-field
      • Explains Polarized RC
    • Re-accelerate CRe’s
      • Explains flat Radio SPX & large-scale gradient
    • Shocks run through thin disk quickly
      • shock ~ 20 - 40 Myr
  • Excess global RC?
    • For typical Virgo parameters: ~3-11% of KE from shock must be given to CR’s to have doubled RC emission.
    • Clearly, shocks have enough energy to explain low q!

Synchrotron Tail



B-field mildly


ICM Driven


ICM Wind

Currently, this is our preferred picture

general conclusions
General Conclusions
  • Distribution of radio/FIR ratios w/in cluster galaxies thought to be experiencing ICM-ISM effects differ systematically from field galaxies:
    • radio/FIR ratios low along edges in direction of ICM wind due to a deficit of radio emission
  • FIR-radio correlation within cluster galaxies appears sensitive to effects of ram pressure
    • Large local radio deficits => Low global FIR/radio ratios
    • Preferred picture: CRe- reacceleration by ICM driven shocks
  • Radio deficits inversely correlated with time since peak pressure as inferred from stellar population studies and gas stripping models
    • The radio deficits may be a powerful diagnostic to quantify ongoing ICM wind direction and strength of current ram pressure!
    • Plasma pressure estimates agree with expected ram pressure strengths
kingfish key insights on nearby galaxies a far infrared study with herschel
KINGFISH:(Key Insights on Nearby Galaxies: A Far-Infrared Study with Herschel)
  • PI’s. R. Kennicutt (EU); D. Calzetti (US)
  • 526 hr approved Herschel OTKP
  • Will build upon success of SINGS
  • 61 nearby galaxies
  • 2 Observational Components:
    • Imaging:
      • 6 bands from 70 - 500m (5 - 35”)
    • Spectroscopic Imaging:
      • 55 nuclear & 50 extra-nuclear star-forming regions
      • Principle atomic ISM cooling lines

([OI]63mm, [OIII]88mm, [NII]122,205mm, [CII]158mm)

  • SINGS + New Ancillary Data:
    • Spitzer, optical + H, NIR, WSRT 22cm, THINGS (HI), BIMA-SONG (CO), IRAM-HERA (CO), CARMA (CO), Nobeyama (CO), SCUBA2 (sub-mm),multi-frequency radio lacking!!!
kingfish er kingfish emission in radio
KINGFISHER:(KINGFISH - Emission in Radio)

e.g. NGC 6946

  • PI’s: E.J Murphy & E. Schinnerer
  • 3 - component program
    • Global spectral indices
      • ~5 bands: GBT + Effelsberg
    • Multi-frequency imaging of SINGS/KINGFISH spectroscopically targeted star-forming regions
      • GBT + EVLA
      • RRL’s as well? -- GBT Pilot Project
    • Complete multi-frequency imaging of 1 (or 2?) very nearby galaxies
      • GBT + EVLA



Proposed (Pilot) GBT RRL + 30 GHz