HI as a tracer of interactions

Bärbel S. Koribalski (ATNF, CSIRO)

ATNF Simulatons Workshop What is HI ?

HI generally stands for the 21-cm line of atomic neutral hydrogen gas – results from the spin-flip of the single electron orbiting the hydrogen nucleus – rest frequency: 1.420405751786 GHz HI is an excellent tracer of galaxy dynamics (in gas-rich spiral and dwarf ) HI is the best tracer of galaxy interactions

ATNF Simulatons Workshop Our Galaxy

(infrared image)

The Magellanic Clouds

SMC LMC Neutral Hydrogen gas distribution in the Magellanic system

HIPASS: Putman et al. 2003 HI Prime Example: The group

M81-M82- NGC 3077

(Yun et al. 1994) The galaxy M 83

1o

ATCA + Parkes HI data (Park, Staveley-Smith et al.) optical image (by Dave Malin, AAO)

ATNF Simulatons Workshop Galaxy Pairs with one-sided HI tails

Arp Arp 270 • D143 = 9.6 Mpc • D = 21.7 Mpc • HI tail: 90 kpc • HI tail: 70 kpc

8 • MHI (tail) = 5 x 10 • MHI (tail) = 5 x 8 M¤ 10 M¤

(Clemens et al. (Appleton et al. 1999) 1987) M5 Arp 215 1 • D = 9.6 Mpc • D = 34 Mpc • HI tail: 90 kpc • HI tail: 54 kpc 8 • MHI (tail) = 5 x 10 9 • MHI = 1.4 x 10 M¤ (Rots et al. 1990) M¤ (Smith 1994, Jogee et al. ATNF Simulatons Workshop 1998) NGC HI rings 5291 • D = 58 Mpc • HI extent: 170 NGC kpc

1533 10 • D = 21 Mpc • MHI = 5 x 10 M¤ • HI extent: 70 kpc

9 • MHI = 7 x 10

M¤

(Malphrus et al. 1997)

Leo Ring

• D = 10 Mpc • HI extent: 200 (Ryan-Weber et al. 2003) kpc • M = 109 M HI ¤ (Schneider et al. ATNF Simulatons Workshop 1989) Overview the asymmetric spiral galaxy NGC 2442 + massive HI cloud “The Antennae” (NGC 4038/9) the giant spiral NGC 6872 + small companion the one-armed spiral M99 in Virgo interacting spiral pair NGC 6221/15 the peculiar NGC 3256 group the spiral IC 2554 + one-sided HI plume ….

ATNF Simulatons Workshop Intergalactic HI gas near NGC 2442 (Ryder, Koribalski et al. 2001)

9 10 M¤ intergalactic HI gas 250 kpc projected separation from the galaxy NGC 2442 No optical counterpart resolved into numerous clumps with the ATCA

HIPASS BGC

NGC 2442 UKS/DSS ATNF Simulatons Workshop

Bekki, Koribalski, Ryder & Couch 2005

ATNF Simulatons Workshop The galaxy pair NGC4038/9

“The Antennae’’ nearby pair of merging galaxies prominent tidal tails in the optical and HI formation in the nuclear disks one companion new in formation

ATNF Simulatons Workshop The galaxy pair NGC4038/9

HI intensity distribution

HI velocity field (top)

ATNF Simulatons Workshop simulations by Toomre & Toomre 1972

ATNF Simulatons Workshop Recent simulation by Barnes & Hibbard N E

IC 4970

NGC 6872

VLT ANTU + FORS1 BVR image (ESO PR 20b/99) ATCA HI data here: an HI peak flux density image Snapshot 140 Myr after perigalacticon Snapshot 140 Myr after periapse:

ATNF Simulatons Workshop

The spiral galaxy Messier 99

M99 is a rather unusual one-armed spiral galaxy.

Reference: DSS2 B-band It’s in the Virgo cluster. VLA HI observations of M99

by Phookun, Vogel & Mundy (1993) Does M99 have a tidal stream ?

HI cloud

HI stream N-body simulations by Kenji Bekki (UNSW)

for a paper by Bekki, Kilborn & Koribalski (2005) Interacting NGC6215 galaxy pair NGC6221/15

NGC6221

Koribalski & Dickey (2004) NGC 3256C NGC The NGC 3256 3256 galaxy group (English & Koribalski 2005) NGC 3263

10’ or • D = 37.6 Mpc 110 • HI cloud extent: kpc ∼175 kpc x 100 kpc • M (cloud) = 109 ESO263- HI G044 M¤

NGC 3256B Zoom-In NGC 3263

To the east: the interacting galaxy NGC 3263 with HI 10 MHI = 2 x 10 M¤ cloud NGC 3262 (v ∼ 2600 to 3300 km/s)

To the west: the giant diffuse HI cloud with ESO263- M 109 M G044 HI ∼ ¤ WPV06 (v ∼ 2760 to 2920 km/s) 0 IC 2554 one-sided HI tail/plume, attached to IC 2554 NGC • D = 16 Mpc 3136B • tail extent: 30 kpc

9 • MHI = 2 x 10 M¤ • HI cloud to galaxy IC mass ratio = 1/3 2554 • potential interaction partner: NGC 3136B,

Δvsys ∼ 400 km/s

(Koribalski, Gordon & Jones 2003)