Chemical clocks for early-type galaxies in clusters
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Chemical clocks for early-type galaxies in clusters Carretero, Vazdekis & Beckman. 2006, MNRAS, in press. Conrado Carretero Alejandro Vazdekis John E. Beckman. Framework: how were galaxies formed?. Our study:.

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Chemical clocks for early-type galaxies in clusters

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Chemical clocks for early type galaxies in clusters

Chemical clocks for early-type galaxies in clusters

Carretero, Vazdekis & Beckman. 2006, MNRAS, in press

Conrado Carretero

Alejandro Vazdekis

John E. Beckman


Chemical clocks for early type galaxies in clusters

Framework: how were galaxies formed?


Chemical clocks for early type galaxies in clusters

Our study:

  • Detailed stellar population (SP) analysis: offer a “fossil record” of galaxy formation and evolution processes.

  • Based on new stellar population models and a new methodology.

  • We concentrate on early-type galaxies since they represent most of the luminous mass of clusters.

  • SAMPLE: 27 massive (250 km/s < s < 450 km/s) elliptical galaxies distributed in 4 very rich clusters (richness class 3).


Chemical clocks for early type galaxies in clusters

Ages

Information obtained from SP

Abundances

We use certain elements as “chemical clocks”:


Chemical clocks for early type galaxies in clusters

Ages

Information obtained from SP

Abundances

  • We use certain elements as “chemical clocks”:

  • Mg Produced by SNe II in ~0.01 Gyr(e.g. Faber, Worthey & González 1992)

  • CN By intermediate-mass stars in ~0.5 Gyr (e.g. Chiappini et al. 2003)

  • Fe Produced, mainly, by SNe Ia in ~1 Gyr(e.g. Hughes et al. 1992)

  • Others…


Chemical clocks for early type galaxies in clusters

C, CN

Fe

Mg

SFR

1 Gyr

0.01 Gyr

0.5 Gyr

TODAY

time

Ages

Information obtained from SP

Abundances

We use certain elements as “chemical clocks”:

SP formation timescales

SHORT

LONG


Chemical clocks for early type galaxies in clusters

The values of the abundance ratios of those elements, measured in a galaxy, are related with the formation timescale of its stellar population.

Do they depend on the environment?

Ages

Information obtained from SP

Abundances

  • We use certain elements as “chemical clocks”:

  • Mg Produced by SNe II in ~0.01 Gyr (e.g. Faber, Worthey & González 1992)

  • CN By intermediate-mass stars in ~0.5 Gyr (e.g. Chiappini et al. 2003)

  • Fe Produced, mainly, by SNe Ia in ~1 Gyr(e.g. Hughes et al. 1992)

  • Others…


Chemical clocks for early type galaxies in clusters

Age

Age

Age

Z

Z

Z

Ages

Information obtained from SP

Abundances


Chemical clocks for early type galaxies in clusters

Results


Chemical clocks for early type galaxies in clusters

Our sample

Coma*

Virgo*

* Taken from Sánchez-Blázquez et al. (2006)

Results


Chemical clocks for early type galaxies in clusters

[CN/Fe] gradient with cluster mass

Results

[Mg/Fe] provides an upper limit for SP formation timescales (~1 Gyr)

while

[CN/Fe] is most suitable to discriminate between different timescales (linked to the environment) but…


Chemical clocks for early type galaxies in clusters

Results

[Mg/Fe] provides an upper limit for SP formation timescales (~1 Gyr)

while

[CN/Fe] is most suitable to discriminate between different timescales (linked to the environment) but…

… only for those galaxies with s < 300 km/s


Chemical clocks for early type galaxies in clusters

Conclusions

  • [CN/Fe] and [Mg/Fe] appear to be the key “chemical clocks” for infering the star formation history timescales in ellipticals.

  • [Mg/Fe] provides an upper limit for those formation timescales, while [CN/Fe] discriminates more finely among them.

  • We estimate an upper limit of <1 Gyr for those formation timescales, independently of their environment and galaxy mass.

  • Star formation history timescales in ellipticals depend on the environment: shorter timescales in denser environments. These differences become smaller as the galaxy mass increases.


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