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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 (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

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  1. Intracluster Shocking of the ISM in Virgo Spirals: Modified FIR-Radio Relations Eric J. Murphy (Caltech) The EVLA: Galaxies Through Cosmic Time

  2. 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

  3. FIR – Radio Correlation: How it works… well, kind of(de Jong et al. 1985; Helou et al. 1985) FIR • 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 SNe synchrotron σ = .26 (L. Cowie) Yun, Reddy, & Condon. (2001)

  4. A C Φ B 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 Smeared 70µm Maps

  5. 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!

  6. 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

  7. 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

  8. Polarized RC on HI Evidence of Ongoing Pressure NGC 4522: A well studied case for ram pressure stripping: Leading edge 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

  9. Pol. on HI NGC 4501 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!

  10. 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

  11. 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!

  12. Severity of Deficit vs. q <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!

  13. 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 sheared B-field mildly compressed ICM Driven Shocklets ICM Wind Currently, this is our preferred picture

  14. 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

  15. 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!!!

  16. KINGFISHER:(KINGFISH - Emission in Radio) e.g. NGC 6946 • BIG THINKING for the EVLA • 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 SINGS+KINGFISH e-nucs SINGS+KINGFISH Radial Strip Proposed (Pilot) GBT RRL + 30 GHz

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