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
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
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
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
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
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
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