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

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 v2 can be ~40 times higher than Virgo

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

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 ClusterROSAT X-Rayon GalaxyCounts

Bohringer etal 1994; Schindler etal 1999

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

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

HI stripped from NGC 4522

0.5L* galaxy with normal stellar diskHas 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

NGC 4522

WIYN BVR

NGC 4522

VLA HI on R

Kenney, van Gorkom & Vollmer 2004

Highly-inclined spirals fromVirgo Cluster VLA HI Survey

Dense extraplanar HI is rare (Crowl etal in prep)

Ram Pressure Simulations N-body Vollmer etal

(2001) Radial orbitsin cluster

Ram pressure vs. time over 1 orbit

Snapshots of galaxy gas distributionduring strippingevent

Large concentrations of extraplanargas seen only in early activestripping phase

-75 Myr 0 Myr

75 150

225 300

375 450

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

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

Vollmersimulation

HI data

50 Myrafter peakpressure

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?

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

6cmPolarizedFlux on HI

Spectral index6/20 cm

Eastern leading edge has:

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

• N4522 is located 3.5o = 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!

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 ISMHas 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 HN4522

HST ACS BVI NGC 4522

B unsharp masked

200 pc

3”

• 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

Mgas>5x104

Msun

200 pc

3”

• 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

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 RN4402

Dust (& GMC?) Stripping in NGC 4402BVR 0.5”WIYN Tip-Tilt

Crowl etal 2005

BVR 0.5”WIYN Tip-Tilt Imager

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 > 5x105 Msun

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

and now... 33 words on theEffects of ICM-ISM stripping on

Nuclear outflows

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

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 HI

summaryClear 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