Spitzer Space Telescope - General Observer Proposal #20606


The evolution of early-type galaxies in nearby clusters:  breaking the
age-metallicity degeneracy with Spitzer IRS Blue Peak-Up Imaging

Principal Investigator: Alessandro Bressan
           Institution: INAF Padova Astronomical Observatory

Co-Investigators:
Pasquale Panuzzo, INAF Padova
Roberto Rampazzo, INAF Padova
Lucio Buson, INAF Padova
Marcel Clemens, INAF Padova
Jose Ramon Valdes, INAOE
Gian Luigi Granato, INAF Padova
Laura Silva, INAF Trieste
Luigi Danese, SISSA

Science Category: galaxy clusters and groups 
 Observing Modes: IracMap IrsPeakupImage 
  Hours Approved: 48.9 

Abstract:
We have shown with Cycle 1 observations that Spitzer has the
capability of disentangling age and metallicity in old stellar
populations.  By looking to the broad emission feature left by dust
enshrouded asymptotic giant branch stars above 9.7 microns, Spitzer
IRS can provide direct evidence that the colour- magnitude relation of
Virgo ellipticals is mainly driven by metallicity.  However, with the
IRS spectrograph we can only probe the bright tail of the
colour-magnitude relation, and only in the nearest cluster.  We
propose to use IRS Blue Peak-Up, the only Spitzer band that looks
directly in the core of that spectral feature, to reach fainter
galaxies.  We will perform a thorough investigation of early type
galaxies along the colour-magnitude relation in Virgo and in Coma
clusters.  These observations, when coupled with already existing IRAC
and Optical-NIR observations, will allow a) an unbiased census of the
stellar populations in cluster early type galaxies;  b) an estimate of
the AGB material recycled into the ISM in these systems;  c) a direct
check of the universality of the colour- magnitude relation on a wide
range of magnitudes;  d) a spatial study of the stellar populations
within the galaxies, e.g.  investigating differences between bulge and
disk populations within S0;  e) the most secure reference frame with
which to compare the evolution of early type galaxies in other
environments (groups and field).