1. Gas stripping and its Effect on the Stellar Populations of Virgo Cluster Galaxies
Hugh H. Crowl
UMass
with
Jeff Kenney (Yale)
Jacqueline van Gorkom (Columbia), Aeree Chung (NRAO), Bernd Vollmer (CDS), Jim Rose (UNC:CH)
Image by A. Chung

2. Stellar Populations in Outer Disks
The age of the last generation of stars will serve as a chronometer to determine when and, thereby, where in the cluster galaxies are stripped.
“red” outer disk
blue outer disk
Older Stellar Population
Stripped longer ago?
Younger Stellar population
Stripped more recently?
SDSS images from website of D. Hogg

3. Evolution of a Stellar Population
Bruzual and Charlot (2003) single burst stellar population evolutionary model.
As a stellar population ages, two of the most dramatically changing quantities are:
UV color (GALEX)
Balmer lines (Optical Spectroscopy) Hb
Starburst 99 Models Hg Hd
Bruzual & Charlot (2003)

4. Observations
Observed on the 3.5m WIYN telescope using the SparsePak formatted field spectroscopy array
λ = 4000 Å – 6700 Å
5.5 Å FWHM resolution
SparsePak Array: 75 fibers in an 80” x 80” field
GALEX photometry of the outer disk, combined with optical spectroscopy, allows us to characterize the SF history for the youngest stellar populations.

5. NGC 4522
Edge-on spiral galaxy in Virgo 3.3° (~1 Mpc) from the cluster core
One of the best known cases for ongoing ISM-ICM interaction
40% of the HI is extraplanar
Kenney et al (2004)
Vollmer et al (2004)
Polarized Radio Continuum on HI
Polarized Radio Continuum at “leading edge” of interaction
Estimates of Ram Pressure from simple models are 10 times too weak to account for observed stripping!

6. NGC 4522: Spectral Observations
Crowl & Kenney (2006)
SparsePak on R
Sparsepak on Hα
Galaxies observed beyond the gas truncation radius, and still within the stellar disk.

7. GALEX photometry constrains the recent star formation
FUV-bright outer disk
GALEX FUV + NUV Image -2 -1 1
log(FFUV/FV) -3
log(FFUV/FNUV)
Galaxy was stripped in its current location, far from the cluster core!

8. VIVA: VLA Imaging of Virgo in Atomic gas

9. Age vs. Cluster Location
If galaxies are only stripped in the center of the cluster, the galaxies with the youngest outer disk ages should be closest to M87
While some disks are consistent with beings stripped in the core, the outer disks of some galaxies are too young to have been stripped there.

10. Global Color Evolution
While we can study galaxies in Virgo in detail, it is much harder to observe the effect of transformation on galaxies in higher redshift clusters
we need to understand the effect of transformation on global properties
The global colors of our VIVA galaxies are quickly affected by the quenching of star formation.
I3392
N4522
N4405
N4569
N4388
N4424
N4064
N4580
N4419
tq~100 Myr
tq~ Myr
tq>400 Myr
Contours: 140K+ SDSS Galaxies (Blanton et al. 2003)
Crosses: VIVA Galaxies

11. older interaction recent interaction I3392 tq>400 Myr N4569

12. Summary
NGC 4522, an example of ongoing stripping, has a young stellar population in its outer disk despite its location in the outer cluster.
In Virgo, some galaxies are stripped outside the core.
It appears that galaxies can have their gas stripped at much larger cluster radii than typically assumed.
The three of our sample galaxies that overlap with gas simulations have truncation ages that agree with the simulation estimates.
Star formation ends shortly after the neutral gas is stripped
Global galaxy colors are affected on timescales of ~400 Myr.
Stellar populations of stripped spirals provide us a unique and useful tool for probing the interaction history of cluster galaxies.

14. IC 3392 ttr ~ 0.5 Gyr NGC 4522 ttr ~ 0.1 Gyr VIVA HI on X-Ray
Cluster Gas Simulation
Tonnesen et al. (2008)
IC 3392
ttr ~ 0.5 Gyr
Shibata et al (2001)
X-Ray Temperature Map
NGC 4522
ttr ~ 0.1 Gyr
VIVA HI on X-Ray

15. Comparison of Stellar Population Ages to Gas Stripping Simulations
Vollmer et al 2006
Time since peak pressure ~ 50 Myr
ttr = 100 ± 50 Myr
Vollmer et al (2004)
Time since peak pressure ~ 300 Myr
ttr = 300 ± 50 Myr

16. Comparison of Stellar Population Ages to Gas Stripping Simulations
Oosterloo & van Gorkom (2005)
ttr = 225 ± 100 Myr
Vollmer et al (2003)
Time since peak pressure ~ 200 – 250 Myr
Time since peak pressure ~ 120 Myr

17. ttr ~ 0.1 Gyr
Spectra show galaxies with very different ages. Are the galaxies in very different environments?
T ~
ttr ~ 0.5 Gyr

18. Time Sequence of Stripping
recent
100 Myr
N4569
300 Myr
intermediate
I3392
HI on R
older
500 Myr
HI on R
WIYN Optical spectra
SDSS Optical image