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

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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
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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
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FIR Radio Correlation How it works well, kind
of(de Jong et al. 1985 Helou et al. 1985)
FIR
SNe
synchrotron
(L. Cowie)
s .26

• 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

Yun, Reddy, Condon. (2001)
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Image Smearing Analysis (e.g. NGC 5194)
Residuals between Radio Smeared FIR
Images (Murphy et al. 2006a,b) B Best-fit
Scale-length F Improvement (x2-3 on average)
22cm Map
A l 0.0 kpc
B l 0.6 kpc
C l 3.0 kpc
Smeared 70µm Maps
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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!

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Looking for Deviations from Expected Radio
Morphology

• 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 gt 1.3
• Deficit regions are detected
• Pix lt 0.50
• Quantify severity of deficit by defining

NGC 4402
NGC 4254
Ratio maps
Deficit regions
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Radio Continuum Deficit/Excess Regions
HI contours overlaid

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

Radio Deficits located opposite synchrotron
tails excess regions - associated with ICM
wind
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NGC 4522 A well studied case for ram pressure
stripping
Leading edge
ICM wind
(Vollmer et al. 2004)
(Murphy et al. 2008 (arXiv08122922)
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
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Polarized Radio Continuum A Diagnostic of Ram
Pressure
Pol. 6cm on Def.
Leading edge
Leading edge
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!

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NGC 4522 Comparison of RC Deficits with SPX
POL data
(SPX POL data from Vollmer et al. 2004)
Flat Spectral Index Re-acceleration
Just Interior to Deficit Region
High Polarization B-field shear/ compression

• 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 enhancement
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Deficit vs. Time Since Peak Pressure

• 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!

(Large deficit)
(Small deficit)

• Deficit region is a good indicator of the
  strength of the CURRENT ram pressure!

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Severity of Deficit vs. q

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

ltqgt
High q
Low q
q log(FIR/Radio)

• Galaxies with large LOCAL radio deficits have
  GLOBAL radio enhancements relative to the FIR!

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Excess Radio CR Reacceleration by ICM Shocks?

• ICM driven shocks
• Compress Shear B-field
• Explains Polarized RC
• Re-accelerate CRes
• 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 CRs to have doubled RC
  emission.
• Clearly, shocks have enough energy to explain low
  q!

RC deficit on 6cm RC and B-field Vectors
Synchrotron Tail
B-field sheared
B-field mildly compressed
ICM Driven Shocklets
ICM Wind
Currently, this is our preferred picture
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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 gt 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

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KINGFISH(Key Insights on Nearby Galaxies A
Far-Infrared Study with Herschel)

• PIs. 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
• (OI63mm, OIII88mm, NII122,205mm,
  CII158mm)
• 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!!!

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KINGFISHER(KINGFISH - Emission in Radio)

• BIG THINKING for the EVLA
• PIs 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
• RRLs as well? -- GBT Pilot Project
• Complete multi-frequency imaging of 1 (or 2?)
  very nearby galaxies
• GBT EVLA

e.g. NGC 6946
SINGSKINGFISH e-nucs SINGSKINGFISH Radial
Strip Proposed (Pilot) GBT RRL 30 GHz