Local post-starburst galaxiesO. Ivy WongSuper Science Fellow @ CSIRO Astronomy & Space Science (Australia)

Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 1

Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 2

Local Universe: useful benchmark for studying galaxy evolution

Redshift

Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 3

Galaxies

?

Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 5

Do galaxies evolve from one type to the other ?& if so,

what/where are these transition-type galaxies?

Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 4

Cosmic Evolution from Galaxy Zoo @ 218th AAS Meeting (Boston) 6

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

s

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

ulat

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