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The mid-infrared colour-magnitude relation of early-type galaxies in the Coma cluster as measured by Spitzer-IRS | | M.S. Clemens
; A. Bressan
; P. Panuzzo
; R. Rampazzo
; L. Silva
; L. Buson
; G.L. Granato
; | | Date: |
21 Aug 2008 | | Abstract: | We use 16 micron, Spitzer-IRS, blue peakup photometry of 50 early-type
galaxies in the Coma cluster to define the mid-infrared colour-magnitude
relation. We compare with recent simple stellar population models that include
the mid-infrared emission from the extended, dusty envelopes of evolved stars.
The K-[16] colour in these models is very sensitive to the relative population
of dusty AGB stars. We find that the passively evolving early-type galaxies
define a sequence of approximately constant age ~10Gyr with varying
metallicity. Several galaxies that lie on the optical/near-infrared
colour-magnitude relation do not lie on the mid-infrared relation. This
illustrates the sensitivity of the K-[16] colour to age. The fact that a
colour-magnitude relation is seen in the mid-infrared underlines the extremely
passive nature of the majority (68%) of early-type galaxies in the Coma
cluster. The corollary of this is that 32% of the early-type galaxies in our
sample are NOT ’passive’, insofar as they are either significantly younger than
10 Gyr or they have had some rejuvenation episode within the last few Gyr. We
also conclude that external effects, such as disruption of the dusty AGB star
envelopes by the interstellar medium, does not effect the 16 micron emission.
This mid-infrared emission is relatively short-lived and occurs well within the
radius at which such effects become important. Given the robustness of
mid-infrared emitting envelopes to environmental effects, the observation that
galaxies with excess 16 micron emission lie preferentially at small radii
within the cluster, indicates that the cluster environment influences the star
formation history. | | Source: | arXiv, 0808.2899 | | Services: | Forum | Review | PDF | Favorites | |
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