We use 16μm, Spitzer-Infrared Spectrograph, blue peak-up 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 Ks- colour in these models is very sensitive to the relative population of dusty asymptotic giant branch stars. We find that the passively evolving early-type galaxies define a sequence of approximately constant age (~10 Gyr) 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 Ks- 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 per cent) of early-type galaxies in the Coma cluster. The corollary of this is that 32 per cent 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.
|Titolo:||The mid-infrared colour-magnitude relation of early-type galaxies in the Coma cluster as measured by Spitzer-IRS|
|Autori:||CLEMENS; M. S; BRESSAN A; A; PANUZZO; P; RAMPAZZO; R; SILVA; L; BUSON; L; GRANATO; G. L|
|Data di pubblicazione:||2009|
|Appare nelle tipologie:||1.1 Journal article|