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),

Gas stripping and its Effect on the Stellar Populations of Virgo

Cluster Galaxies

Hugh H. CrowlUMass

with

Jeff Kenney (Yale)

Jacqueline van Gorkom (Columbia), Aeree Chung (NRAO),

Bernd Vollmer (CDS), Jim Rose (UNC:CH)

Image by A. Chung

Stellar Populations in Outer Disks

“red” outer disk blue outer disk

SDSS images from website of D. Hogg

Older Stellar Population

Stripped longer ago?

Younger Stellar population

Stripped more recently?

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.

Evolution of a Stellar Population•As a stellar population ages, two of the most dramatically changing quantities are:

– UV color (GALEX)

– Balmer lines (Optical Spectroscopy)

Bruzual & Charlot (2003)

Bruzual and Charlot (2003) single burst stellar population evolutionary model.

H

-8

-6

-4

-2

0

2

4

6

0 5 10

Time S ince Truncation (Gyr)

Lin

e S

tren

gth

(A

ngs

trom

)

Starburst 99 Models

H

H

H

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.

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

Kenney et al (2004)

Vollmer et al (2004)

Polarized Radio Continuum on HI

40% of the HI is extraplanar

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!

NGC 4522: Spectral Observations

SparsePak on R Sparsepak on Hα

Galaxies observed beyond the gas truncation radius, and still within the stellar disk.

Crowl & Kenney (2006)

GALEX photometry constrains the recent star formation

FUV-bright outer disk

GALEX FUV + NUV Image

-2 -1 0 1

log(FFUV/FV)

0

-1

-2

-3lo

g(F

FU

V/F

NU

V)

Galaxy was stripped in its current location, far from the cluster core!

VIVA: VLA Imaging of Virgo in Atomic gas

http://www.astro.yale.edu/viva/

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.

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

N4569N4388N4424

N4064

N4580

N4419

tq~100 Myr

tq~200-300 Myr

tq>400 Myr

Contours: 140K+ SDSS Galaxies (Blanton et al. 2003)

Crosses: VIVA Galaxies

I3392

N4522

N4569

tq~100 Myr

tq~200-300 Myr

tq>400 Myr

older interaction

recent interaction

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.