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

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

HI maps blown up by 10x 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

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!!

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

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

Radio evidence for ongoing ram pressure 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) Spitzer 70um VLA 6cm Smoothed 70um/6cm ratio Radio deficit --> Murphy etal 2008; See Murphy POSTER! NGC 4402

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

“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

Polarized Ridges & radio deficits due to ram pressure 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 6cm Polarized Flux on HI Radio deficit on 6cm Polarized Flux Vollmer etal 2004

Deficit region: radio surface brightness is less than 50% of expected strength Deficit parameter: (flux Model - flux observed ) deficit region global radio flux Ram pressure probably strongly correlated with radio deficit parameter

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

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

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

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

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

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 Ha 24um Ha/24 NGC /Ha vs radius extraplanar Leading edge See Wong POSTER!

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

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

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! OPT FUV, NUV 24u + Ha WIYN GALEX SPITZER+WIYN

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

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

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