Transcript How does dust affect estimates of galaxy ages?

How does dust affect estimates
of galaxy ages?
By Justin Griggs
Supervisor: Jason Melbourne
Advisor: David Koo
Outline
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Background information
Methods
Results
Limitations of the method
Conclusion
Acknowledgements
Light Emission is Indication of:
• Age
• Temperature
• Dust
The Effects of Dust:
•Redder
Appearance
•Older, yet Cooler
look
Examples of Real Galaxies
Young
Galaxies
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Old
Dusty
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B-V [colors]
0.289
0.883
0.667
Color
Bluer
Redder
In between
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No Dust
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Lots of Dust
Use Adaptive Optics to estimate the age of
galaxies with dust
Method
Experimental
Models
Program
reads in files
Random
photometric
error
Compares 1
model to all
ages
Calculate
probability
Plot of age vs.
dust using
probability
Sample: 5x5 array
Models
•219 ages
Old
•14 dust models
•SSP star
formation
Age
•3-8 colors
•Photometric
error: 5-50%
Young
Less
Wavelength
Dust
More
= Model + error
Program
Wavelength
Sample: 5x5 array
Age
Old
Young
Less
Dust
More
Results
Use probability to plot age vs dust to narrow
down “good” models by eliminating “bad” ones.
•Using different colors (with and without AO)
•Using different errors (high-low)
•Standard model: dust=0
Bad estimate
Good estimate
Bad estimate
•3 colors
•Age~8.00 log yrs.
10 billion
years
•Photometric error: ~10%
10 million
years
Hubble Space
Telescope (HST)
without Adaptive Optics
Less Dust
More Dust
•Standard model: dust=0
Bad estimate
Good estimate
Bad estimate
•6 colors
•Age~8.00 log yrs.
10 billion
years
•Photometric error: ~10%
10 million
years
HST + Adaptive
Optics
Less Dust
More Dust
•Standard model: dust=0
Bad estimate
Good estimate
Bad estimate
•8 colors
•Age~8.00 log yrs.
10 billion
years
•Photometric error: ~10%
10 million
years
Future?
Less Dust
More Dust
•Standard model: dust=1
Bad estimate
Good estimate
Bad estimate
•6 colors
•Age~9.00 log yrs.
•Photometric error: ~20%
10 billion
years
10 million
years
HST + Adaptive
Optics with high
photometric error
Less Dust
More Dust
•Standard model: dust=1
Bad estimate
Good estimate
Bad estimate
•6 colors
•Age~9.00 log yrs.
•Photometric error: ~10%
10 billion
years
10 million
years
HST + Adaptive
Optics with medium
photometric error
Less Dust
More Dust
•Standard model: dust=1
Bad estimate
Good estimate
Bad estimate
•6 colors
•Age~9.00 log yrs.
•Photometric error: ~6%
10 billion
years
10 million
years
HST + Adaptive
Optics with low
photometric error
Less Dust
More Dust
Limitations
• Dust models are simple
• Galaxy star formation model is very
simple (SSP)
Conclusion
Dust Causes galaxies to appear redder and
thus older than their actual age.
Adaptive Optics vs. HST:
•AO enables estimates of ages to be
within 25% accuracy for a photometric
error of 10%
•Age estimates better with photometric
error between 5 and 10%
Acknowledgements
• Funding provided through the Center
For Adaptive Optics, a National Science
Foundation Science and Technology
Center (STC), AST-987683
• Jason Melbourne, Post doc in
astronomy at UCSC
• David Koo, professor in astronomy at
UCSC