HI Gas as Function of Environment

When and where do galaxies stop accreting cool gas?

How do they loose the cool gas?

When do they stop forming stars?

The lore.. if halos get too big, gas does not coolBut.. at least some dry mergers are wet, and forming stars

Donovan, Hibbard, an Gorkom, astroph-07060734

Jen Donovan poster

Gas content and star formation rate begin to decline in dense group environment and outskirts of clusters

The outskirts of clusters

Solanes et al find smooth variation of HI deficiency out to 2 RA

This agrees nicely with results obtained on smoothly varying star formation rate out to 2 RA

In clusters at intermediate z: Balogh et al 1998

In 2dF : Lewis et al 2002

In Sloan: Gomez et al 2003; Nichol 2004

General conclusion star formation declines if galaxy density exceeds a certain value

The outskirts of Virgo

The outskirts of other (nearby) clusters

The outskirts in simulations

The future in HI work

Possible Drivers for Environmental Evolution

Gravitational

galaxy galaxy : slow encounters mergers - tidal structures galaxy cluster : tidal stretching galaxy many galaxies: harassment cumulative effect of many fast encounters truncates or destroys small galaxies Affects both gas and stars

Gas dynamical effects

ram pressure stripping

turbulent viscous stripping

conduction

Affects only the gas

Starvation

removes left over gas reservoir that fuels star formation

VIVA

VLA Imaging of Virgo Galaxies in Atomic Gas

Aeree Chung, Hugh Crowl, Kenney, van Gorkom, Vollmer

Select galaxies over wide range of local densities

Select galaxies with wide range of star formation properties

Identify galaxies undergoing trauma

Make sophisticated guess as to what is happening

Use simulation to make a more sophisticated guess

Compare timescales from stellar population synthesis with timescales from simulation

Viva-poster

SubgroupsSmall gas disks (compared to the

stellar counterpart) around the cluster

center

Comparable or more extended than the stellar

disks

Small gas disk further away from the cluster center

Tails 2

Can these tails be formed by ram pressure stripping?

Five galaxy tails could have been formed by ram pressure

N4654 probably combination of gravitational and rp

N4396 possibly also, or viscous stripping

HI TAIL Galaxies

We see for the first time galaxies being affected at intermediate distances.

These are galaxies radially falling in

Their gas is being removed by ram pressure and/or by gravitational interaction

Chung, van Gorkom, Kenney, Vollmer, ApJ L in press

NGC 4522

This galaxy is different, though far out in cluster, it is stripped well to within the disk

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

Young Stellar Population in Stripped Outer Disk of NGC 4522

Strong Balmer lines and bright FUV emission in stripped outer disk indicate star formation stopped only ~100 Myr ago --> disk was stripped recently

Crowl & Kenney 2006

GALEX FUV+NUVOPT + HI

NGC 4522 is stripped locally and not in core

• NGC 4522 cannot travel far in 100 Myr, so must be stripped locally & not in cluster core

• NGC 4522 is located 3.5o = 0.8 Mpc from

M87

• Time to reach core ~700 Myr

Asca data Shibata et al 2001

M49 subcluster falling in 1300km/s

ICM velocity could increase ram pressure by factor 10 ongoing stripping

2 tails pointing toward M49

Just south of NGC 4522

Oosterloo and van Gorkom, 2005

HI tail probably due to ram pressure stripping

Within disk HI stripped

No optical counter part at position of tail

Length 125 kpc .. To get that long few x 108 yr

Peaks near M86 .. High enough to get star formation

In X ray.. Low temperature and high abundance region near tip of tail (Finoguenov et al 2004 XMM)

M86 group colliding with M87 and with high velocity group at 2000 km/s

Conclusions from HI imaging of selected galaxiesIn center we see very small HI disks.. Almost certainly due to ram pressure stripping

The stripping is important for the evolution of the galaxies.

H alpha imaging (Koopmann Kenney 1998, 2004) shows that Virgo galaxies have reduced star formation rates compared to the field. This is primarily caused by truncation of starforming disks. A strong correlation is found between HI deficiency and normalized H alpha flux

We see for the first time galaxies being affected at intermediate distances. Galaxies falling in radially are being affected by ram pressure

and/or gravitational interactions

Some galaxies at large distances being affected by strong rampressure. These galaxies are very HI deficient.

Evidence for a dynamic ICM

A2670A496

A85

A754

Detection rates in volume limited surveys

Hydra 50 galaxies pre merger

A2670 50 galaxies pre merger

A496 25 galaxies beginning merger

A85 10 galaxies ongoing merger

A 754 1 galaxy just past merger

Detection rate depends on dynamical state of cluster

Movies by Greg Bryan (http://www.astro.columbia.edu/~gbryan/movies)

using a hybrid adaptive mesh refinement algorith

gaseous component, starformation, dark matter and stars

(ENZO)

1. Gas temperature: cosmological simulation of cluster assembly

2. High resolution gas density: evolution of 1 cluster

3. High resolution: HI

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

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QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

0-1 Mpc 1-2.4 Mpc 2.4 - 5 Mpc

Changes in cool gas mass for the galaxies that have no changes in stellar mass.

Gas loss Gas accretion

Ram pressure as function of distance from center

Conclusions from simulations

(Stephanie Tonnesen, Bryan, JvG 2007 ApJ, in press)

Observe mergers in central region as well as periphery, none are dry. None of the mergers exhaust gas supply of participating galaxies

Ram pressure effective beyond central region, although most gas loss within 1 Mpc. Timescales 1 Gyr or more.

Ram pressure begins in transition region for half of ram pressure stripped galaxies and in one case in periphery

Galaxies in periphery often accrete cool gas, this stops between 1-2.4 Mpc, indicating the onset of starvation

HI imaging of clusters at z=0.2

Verheijen et al, 2007, ApJL in press

We probe a HUGE volume,

8.2Mpc x 8.2 Mpc x 18000 km/s (326 Mpc) 1.7 x 104 Mpc3

We detect galaxies…. Can even derive rotation curves

Stacked spectra of non detected galaxies

No detection of blue B-O galaxies detection of blue field galaxies

It is location of B-O galaxies that makes them different