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Jeff Kenney (Yale)

Jeff Kenney (Yale). Spitzer Studies of Environmental Effects in Virgo Spiral Galaxies. E. Murphy G. Helou A. Abramson I. Wong J. Howell J. Van Gorkom B. Vollmer H. Crowl A. Chung. Jeff Kenney (Yale). Spitzer Survey of Virgo (SPITSOV). SAMPLE 44 S0/a-Sm Virgo spirals

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Jeff Kenney (Yale)

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  1. Jeff Kenney (Yale) Spitzer Studies of Environmental Effectsin Virgo Spiral Galaxies E. Murphy G. Helou A. Abramson I. Wong J. Howell J. Van Gorkom B. Vollmer H. Crowl A. Chung Jeff Kenney (Yale)

  2. Spitzer Survey of Virgo (SPITSOV) SAMPLE • 44 S0/a-Sm Virgo spirals • Throughout cluster • Range of HI & Ha properties DATA • IRAC & MIPS • 36 new galaxies, 8 SINGS/other • 2x SINGS depth GOAL environmental effects on galaxy evolution STUDY ISM, star formation, stellar pops & morphology OTHER DATA VLA HI & radio, GALEX UV, optical BVRIHa, optical spectroscopy (kin & stellar pops) PLUS.. Simulations

  3. VIVA VLA Imaging of Virgo Galaxies in Atomic Gas Aeree Chung Hugh Crowl Jacqueline van Gorkom Jeff Kenney Bernd Vollmer VLA HI maps on X-ray HI maps blown up by 10x

  4. Today’s talk: Focus on galaxies experiencing ram pressure stripping • 70um + radio: “radio deficits” indicate strength and direction of ram pressure • 24um + Ha: less obscured star forming regions at leading & outer edges & in extraplanar regions • 8um & optical extinction: reveals dust geometry, which constrains interaction models See POSTERS by Abramson, Murphy & Wong!!

  5. HI stripped from NGC 4522 NGC 4522 Kenney, van Gorkom & Vollmer 2004 VLA HI on R IRAC 0.5L* galaxy with normal stellar disk Has only 25% of normal HI (HI def =0.6) HI truncated in disk at 0.3R25 extraplanar ISM on only one side of disk [40% of total HI and 5% of total 8um is extraplanar] Can we measure ram pressure acting now on galaxy?

  6. Using Spitzer FIR and radio maps to trace ram pressure • Use Spitzer FIR maps and radio-FIR correlation to predict radio distribution expected for non-interacting galaxy • Hypothesis: some differences between actual and expected radio distributions are due to ongoing ram pressure • “Radio deficit regions” may be good indicator of strength and direction of current ram pressure • Shows how different parts of ISM react differently to external pressure

  7. Radio evidence for ongoing ram pressure <--Radio excess --> Radio deficit --> • Excellent FIR-radio correlation in normal galaxies allows one to predict radio map for undisturbed ISM from FIR map • Differences between actual & predicted radio maps due to external influence (ICM ram pressure) VLA 6cm Smoothed 70um/6cm ratio NGC 4402 Murphy etal 2008; See Murphy POSTER! Spitzer 70um

  8. Deficit region: radio surface brightness is less than 50% of expected strength

  9. “Radio deficit” regions at leading edges of ram pressure interactions • Relativistic magnetized plasma which produces radio emission is easier to disturb than the denser components of the ISM • Selective disturbance to radio halo is diagnostic for strength & direction of ram pressure RC deficit Regions on Radio maps Murphy etal 2008

  10. Polarized Ridges & radio deficits due to ram pressure 6cm Polarized Flux on HI • Radio deficit region is located outside ridge of enhanced polarization • Radio plasma “far” from dense ISM is pushed away, radio plasma “near” dense ISM is compressed & sheared Radio deficit on 6cm Polarized Flux Vollmer etal 2004

  11. Deficit region: • radio surface brightness is less • than 50% of expected strength • Deficit parameter: • (fluxModel - fluxobserved )deficit region • ----------------------------------------------------- • global radio flux Ram pressure probably strongly correlated with radio deficit parameter

  12. Local radiodeficitparameter Global log (FIR/radio) Murphy etal 2008 Galaxies with LOCAL radio deficits seem to have GLOBAL radio enhancements!! Shocks driven into ISM by ram pressure?

  13. Gas Stripped Spiral NGC 4569can we find clear evidence of stripping in galaxies which are not highly inclined? OPT IRAC Spitzer 3,4,5+8um (SINGS) SDSS gri (Hogg) VLA HI on R-band (VIVA) Virtually no ISM in outer disk due to ram pressure stripping

  14. Remaining ISM in central 6 kpc of stripped spiral NGC 4569 note anomalous ISM West of truncated gas disk --> Gas stripped from disk Kenney etal 2008

  15. Dust extinction vs. emission Constrains ISM geometry & stripping model Anomalous W gas & dust: Less extinction than expected for dust in disk W dust/gas is behind diskas expected for gas stripped from galaxy moving toward us

  16. Tracing star formation in stripping galaxies Example: NGC 4402, great case of stripping in action HI on R-band Radio pol on R-band Radio on R-band Radio deficit on radio Crowl etal 2005; Vollmer etal 2007; Murphy etal 2008

  17. NGC 4402 Ha Star forming regions with high H/24m ratios in stripping galaxies • Leading/outer edges -- dust partly blown away by ram pressure • Extraplanar -- low density of ISM (dust) and heating sources 24um 24/Ha vs radius Leading edge extraplanar Ha/24 See Wong POSTER!

  18. NGC 4330 Radio deficit on HI Star forming regions with high Ha/24um: Leading edge & outer edges & extraplanar Ram pressure induced SF at leading edge is modest Abramson etal 2008; See Abramson POSTER!

  19. Dust & gas blown away from star forming regions at leading edge of ram pressure interaction • NGC 4402’s l-o-s motion in cluster is toward us --> we see leading edge WIYN BVR (0.5” res) Crowl etal 2005

  20. OPT WIYN • Star forming complexes at leading edge bright in UV, faint in IR • Dust stripped away • Star formation enhanced or just revealed? • May need to add UV to 24u+Ha to get ‘total’ SFR • VERY unobscured star forming regions! FUV, NUV GALEX 24u + Ha SPITZER+WIYN

  21. summary • 70um + radio: radio deficits (wrt smoothed 70um) indicate strength and direction of ram pressure • 24um + Ha: less obscured star forming regions at leading & outer edges & extraplanar regions • 8um & optical extinction: reveals dust geometry, which constrains interaction models • Ram pressure induced star formation seems modest (but may need to include UV in SF estimates) • MIR-FIR (8-160um) is weak (>2-10x) wrt HI, Ha in stripped extraplanar gas, due to low ISM density & less heating

  22. Evidence of Ongoing Pressure from Radio Continuum in NGC 4522 Vollmer, Beck, Kenney & van Gorkom 2004 Flattest spectral index (-0.7)  local electron acceleration suggestive of shock 6cm Polarized Flux on HI Spectral index 6/20 cm Eastern leading edge has: Enhanced 6cm polarization  suggests compressed magnetic field

  23. Dust extinction vs. emission Constrains ISM geometry & stripping model More extinction than expected for dust in disk --> SE gas/dust spur is in front of disk -- wrong side!?! Gas infall after peak pressure? Less extinction than expected for dust in disk --> W dust/gas is behind disk, as expected for gas stripped from galaxy moving toward us

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