Collisional ISM Heating in Ellipticals: the Case of M86

Jeffrey Kenney (Yale)Tomer Tal (Yale)Hugh Crowl (Yale)John Feldmeier (YSU)George Jacoby (WIYN)

SDSS gri

SDSS griKPNO MOSAIC H+[NII]

M86

Separation 23’ = 115 kpc

NGC 4438

Kenney etal 2008

H velocities fromWIYN Sparsepak

X-ray (ROSAT)HI (VLA)H(KPNO 4m)

NGC 4438 (Arp120)• very HI-deficient

<10% “normal” HI• ~5x109 Msun of HI

“missing”

X-Ray on H

B H

HI on B

HI: Hota etal 2007 X-ray: Machacek etal 2004

M(HI) = 2x108 Msun

M86X-ray (Chandra: Randall etal 2008) HI (VLA: Li & van Gorkom 2001)

H

Collisional KE should be significant heating source for

M86 ISM• Kinetic energy of gas stripped from

NGC 4438 by gaseous halo of M86 1/2Mv2 = 1/2 (5x109Msun)(1000 km/s)2 =

5x1058 erg

compare to:• Thermal energy of M86 ISM nkTV = (10-3 cm-3)(0.8 keV)(4/3)(73 kpc)3

= 6x1058 erg

• H evidence for a previously unknown high-velocity collision between M86 and highly disturbed spiral NGC 4438 (during subcluster merger)

• HI stripped from NGC 4438 by ram pressure during passage through M86 ISM leaves debris trail of gas heated by ram pressure drag /collisional excitation/shocks/thermal conduction (?) from hot ISM of M86, producing H filaments

Relevant for current major problem in galaxy formation/evolution: how to prevent continued star formation and stellar growth of largest galaxies

• Large collision KE~1059 erg from stripped gas should contribute to heating of M86 ISM, inhibiting “cooling flow”, star formation and BH fueling

• M86 has very weak radio source, so AGN heating of ISM unlikely at present

• Although extreme case, ISM easy to study in M86: should teach us about general importance of gravitational ISM heating in ellipticals

Kenney etal 2008

A 3rd galaxy

involved?HI tail from NGC 4388

(Oosterloo &

van Gorkom 2005)

High velocity (2000-2500 km/s) HI (WRST) and H tail from NGC 4388 (contours, green)

Low velocity (-600 to +100 km/s) H between M86 and NGC 4438 (red)

Implication for EVLA

• Some galaxies/clusters have very large range of velocities, which cannot be observed with VLA correlator

• But CAN BE with EVLA correlator

Chandra X-rayRandall etal 2008