Local post-starburst galaxies - ICG...
Transcript of Local post-starburst galaxies - ICG...
Local post-starburst galaxiesO. Ivy WongSuper Science Fellow @ CSIRO Astronomy & Space Science (Australia)
Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 1
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Local Universe: useful benchmark for studying galaxy evolution
Redshift
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Galaxies
?
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Do galaxies evolve from one type to the other ?& if so,
what/where are these transition-type galaxies?
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What is a local post-starburst?➡ Local galaxies (0.02 < z < 0.05) whose SF has recently gone through a sudden truncation where Balmer absorption lines are still evident from the youngest stars but no on-going SF is observed
Post-s
tarb
urst
?
?
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Local post-starburst galaxies from Galaxy Zoo
Early-type (16%) Intermediate-type (74%) Late-type (10%)PSG:
Early-type (19%) Intermediate-type (47%) Late-type (34%)All:
Wong et al. (2011, submitted to MNRAS)
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Color & Mass
➡ Distinct concentration in low-mass end of the “green valley”- below the Kauffmann transition mass (Kauffmann+03)
Wong et al. (2011, submitted to MNRAS)
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log (Stellar mass)
9.0 9.5 10.0 10.5 11.0 11.5 12.0log (Stellar Mass) [MSUN]
0.01
0.10
Perc
enta
ge o
f PSB
gal
axie
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Wong et al. (2011, submitted to MNRAS)
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➡ structurally, local green valley PSG are similar to early-types (KS probability = 0.7)
Stellar concentration
Fraction of light fitted by a de Vaucouleur profile
PSGAll late-types
PSG
All early-types
Wong et al. (2011, submitted to MNRAS)
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Environment
➡ The local environment of our PSG follow that of the general galaxy population
Early-typesLate-typesIndeterminatePSG
Low density Medium density High density
Wong et al. (2011, submitted to MNRAS)
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Interactions?
➡ Although many appear disturbed/asymmetrical, their fm parameter suggest that they are not ‘strongly-disturbed’/fm>0.4 (Darg+2010)
0.00 0.05 0.10 0.15 0.20fm
0.7
0.8
0.9
1.0
Nor
mal
ized
cum
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ive
dist
ribut
ion
of f m
Early-typesLate-typesIndeterminatePSG
Weighted merger vote fraction (fm)
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Summary
➡ Distinct concentration in low-mass end of the “green valley”- below the Kauffmann transition mass (Kauffmann+03)
➡ Stellar structure of PSG resembles those of early-types- unless SF restarts, PSG will move up to the red sequence
within the timescale needed for the latest generation of young stars to redden
➡ Consistent with downsizing (smaller things form later)- so PSG contribute to the build-up of low mass-end of the red sequence