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 cool But.. at least some dry mergers are wet, and forming stars Donovan, Hibbard, an Gorkom, astroph 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 R A This agrees nicely with results obtained on smoothly varying star formation rate out to 2 R A 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

Subgroups Small 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 L* 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

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+NUV OPT + 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 3.5 o = 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 10 8 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 galaxies In 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

A2670 A496 A85 A754

Detection rates in volume limited surveys Hydra 50 galaxies pre merger A galaxies pre merger A galaxies beginning merger A85 10 galaxies ongoing merger A galaxy just past merger Detection rate depends on dynamical state of cluster

Movies by Greg Bryan ( ) 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

0-1 Mpc Mpc 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 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 km/s (326 Mpc) 1.7 x 10 4 Mpc 3

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