Spitzer Space Telescope - General Observer Proposal #3535


The Ages and Mass Loss Rates of Elliptical Galaxies

Principal Investigator: Joel Bregman
           Institution: Univerisity of Michigan

Co-Investigators: 
Jesse Bregman, NASA-Ames Research Center                              
Pasquali Temi, NASA-Ames Research Center                              

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: IrsStare 
  Hours Approved: 12.8 

Abstract:
The ages of elliptical galaxies are traditionally determined through
absorption line indices where investigators must contend with the
age-metallicity degeneracy and contamination by a few young stars.
These studies result in a wide range of mean ages, 2-18 Gyr,
suggesting that many ellipticals are relatively young, which has
implications for models of elliptical galaxy formation and evolution.
An independent and possibly more powerful age diagnostic for these
galaxies is the collective mass loss rate of the stars, since it
decreases as age^-1.35.  We can to determine the collective stellar
mass loss rate in a galaxy by measuring the silicate emission feature
near 10um, which is produced during stellar outflow in AGB stars.  We
detected this feature in a few early-type galaxies with ISO, but with
the IRS, we propose to measure the silicate emission accurately and as
a function of radius for a sample of 31 galaxies with the best
available optical absorption line ages.