Gas stripping and its Effect on the Stellar Populations of Virgo Cluster Galaxies Hugh H. Crowl...
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Transcript of Gas stripping and its Effect on the Stellar Populations of Virgo Cluster Galaxies Hugh H. Crowl...
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!
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
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.