1. ICM-ISM Stripping in Virgo Cluster Spiral Galaxies Jeff Kenney (Yale University) with: J. Van Gorkom B. Vollmer H. Crowl * A. Abramson A. Chung J. Cortes S. Hameed R. Koopmann T. Tal

2. Importance of ICM-ISM interactions Most spiral + dwarf galaxy gas gets stripped and joins the ICM MUCH higher than stellar stripped fraction Major source of metals in ICM In Virgo spirals, ICM-ISM is dominant mechanism for causing altered SFRs and gas distributions In rich clusters, ram pressure  v 2 can be ~40 times higher than Virgo

3. What we’d like to know about ICM-ISM interactions What actually happens in ICM-ISM interactions? What is more important: ram pressure or hydrodynamic effects? How does complex multi-phase ISM respond to ICM pressure, especially molecular clouds? Does gas get pushed outwards from disk but later fall back? When does HI become ionized & by what mechanism? How do rates of triggered star formation and gas removal by stripping compare?  STUDY GALAXIES WITH ONGOING ICM-ISM INTERACTIONS AT HIGH RESOLUTION

4. Virgo cluster Nearest ‘real’ cluster (D~16 Mpc) Has significant x-ray emitting ICM and many HI-deficient galaxies Dynamically young, ongoing mergers with M86 and M49 subclusters, and infall of galaxies Virgo Cluster ROSAT X-Ray on Galaxy Counts Bohringer etal 1994; Schindler etal 1999

5. Truncated H  disks in Virgo spirals Over 50% of Virgo spirals have truncated H  disks and are HI deficient (Koopmann & Kenney 2004) This includes galaxies stripped a long time ago as well as ongoing interactions

6. Virgo spirals with truncated H  disks and extraplanar HII regions  Active stripping Seen in only 2 of 63 Virgo spirals imaged in H  Koopmann & Kenney 2004

7. HI stripped from NGC 4522 0.5L* galaxy with normal stellar disk Has only 25% of normal HI (HI def =0.6) HI truncated in disk at 0.3R 25 extraplanar HI (40% of total) on only one side of disk NGC 4522 WIYN BVR NGC 4522 VLA HI on R Kenney, van Gorkom & Vollmer 2004

9. Highly-inclined spirals from Virgo Cluster VLA HI Survey Dense extraplanar HI is rare (Crowl etal in prep)

10. Ram Pressure Simulations N-body Vollmer etal (2001) Radial orbits in cluster Ram pressure vs. time over 1 orbit Snapshots of galaxy gas distribution during stripping event Large concentrations of extraplanar gas seen only in early active stripping phase -75 Myr 0 Myr 75 150 225 300 375450

11. Ram Pressure Simulations of NGC 4522 N-body Vollmer (2005)

12. HI morphology in NGC 4522 Large amounts of extraplanar HI close to disk truncation radius  early stage of active stripping HI asymmetry: in SW, disk has less HI, halo has more HI  Gas more easily stripped on side rotating into ICM wind Vollmer simulation HI data 50 Myr after peak pressure

13. HI Kinematics of NGC 4522 Both extraplanar concentrations Blueshifted toward cluster velocity SW extraplanar gas has Large linewidths (150 km/s FWZI) including Blueshifted tail  acceleration of extraplanar galaxy gas toward cluster velocities?

14. 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 2004 6cm Polarized Flux on HI Spectral index 6/20 cm Eastern leading edge has:

15. Stellar Population of Stripped Outer Disk in NGC 4522 Strong recent star formation in stripped outer disk EW(H  ) = 5 Angstroms similar to E+A’s !! Crowl etal, in prep

16. N4522 is located 3.5 o = 0.8 Mpc from M87 where x-rays from cluster ICM are weak Predicted ram pressure at this location for smooth static ICM with n = 10 -5 cm -3 v = 1500 km/s is 10X too weak to cause observed stripping Either ram pressure ~10x higher than that for static smooth ICM (dynamic, lumpy ICM due to AGN heating or sub- cluster mergers) Or hydrodynamic stripping processes are more effective than rps!

17. Is Molecular gas effectively stripped? Important for galaxy evolution and gas mass which enters ICM H  and HI truncation radii the same, HII regions throughout the extraplanar HI 10% of total H  is extraplanar  Star-forming part of ISM Has been effectively stripped! BUT… GMCs are too dense to remove directly via ram pressure ?!? GMCs may be ablated after surrounding low density ISM is stripped by ram pressure HI on H  N4522

18. HST ACS BVINGC 4522 B unsharp masked

19. 200 pc 3”

20. No dust clouds in disk plane beyond gas truncation radius  GMCs gone GMCs quickly ablated after low density surrounding gas is stripped by ram pressure Head-tail dust filaments: Length ~ 100 pc M gas >5x10 4 M sun 200 pc 3”

21. NGC 4522 is moving away from us through cluster, so leading edge of interaction is on far side BUT!!! NGC 4402 is moving toward us through cluster, so leading edge of interaction is on near side, where we can see it more easily

22. NGC 4402 Later stage of stripping? Active but low ram pressure? Only a little extraplanar HI (6% vs. 40% in N4522) Radio continuum strongly asymmetric and skewed to NW Easier to push RC halo than strip disk gas Crowl, Kenney, van Gorkom & Vollmer 2005 HI on R N4402

23. Dust (& GMC?) Stripping in NGC 4402 BVR 0.5” WIYN Tip-Tilt Crowl etal 2005 BVR 0.5” WIYN Tip-Tilt Imager

24. Dust filaments & RC have same PA, indicating ICM wind direction 4” = 300 pc Crowl, Kenney, van Gorkon & Vollmer 2005 Head-tail dust filaments: Length ~ 1000 pc Width ~ 100 pc Mgas > 5x10 5 Msun

25. Ablation of Giant Molecular Clouds at Edge of Gas Disk Edges of gas disk being ablated by hydrodynamic processes Low density gas stripped first, dense clouds survive a while but are quickly ablated

26. and now... 33 words on the Effects of ICM-ISM stripping on Nuclear outflows

27. Asymmetric nuclear outflow in NGC 4438 Nuclear outflow shell is 10x weaker, 2.5x longer in E than W (for Ha & RC & X-ray) Can be explained by outflow into less dense ISM on E side, due to stripping of gas & displacement to W HST BVRH  10” 750 pc Kenney & Yale 2002

28. Asymmetric Starburst Outflow in NGC 4569 Extraplanar gas arm – stripped from disk One-sided starburst outflow nebulosity  Outflow runs into denser ISM on side with stripped gas arm NGC 4569 (M90) WIYN BRIH  Kenney etal, in prep HH HI

29. summary Clear evidence that NGC 4522 is experiencing strong & ongoing ICM-ISM interaction Ram pressure from static smooth ICM too weak by ~10x to cause observed stripping EITHER ICM is dynamic and/or lumpy OR stripping helped by hydrodynamic processes which are much more effective than rps Dust filaments in N4522 and N4402 show that low density gas stripped first, then dense clouds quickly ablated  hydrodynamic processes important & GMCs do not survive long Asymmetric AGN/SB nuclear outflows result from host galaxy ISM which are disturbed by ICM-ISM interactions