Spitzer Space Telescope - General Observer Proposal #30444


IRS Assessment of Star Formation and Galactic Evolution in Ellipticals
with resolved Cold ISM

Principal Investigator: Jacqueline Davidson
           Institution: USRA

Co-Investigators: 
Lerothodi Leeuw, Rhodes University, South Africa                      
Jesse Bregman, NASA Ames Research Center                              

Science Category: Nearby Galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: IrsStare 
  Hours Approved: 11.7 

Abstract:
We propose to use Spitzer-IRS to measure the mid-IR spectral features
of polycyclic aromatic hydrocarbons (PAHs) and silicates from a sample
of nearby, elliptical galaxies.  This sample of galaxies covers a
range of merger tracers or ages, and more importantly is a sample
where recent observations have resolved cold gas and dust emission.
The emission from the cold ISM in these ellipticals is more compact
than their stellar distributions, and may imply star-formation
activity in these compact regions fueled by gas and dust externally
accreted and decoupled from the stellar components.  Our primary aim
with these Spitzer observations is to obtain PAH and silicate,
long-slit spectra that can be used as an independent measure of the
level and period of star-formation activity and its spatial
distribution within these galaxies.  The secondary aim is to use the
IRS intensity and spatial data in comparison with the resolved cold
gas and dust images to gain more information about the nature and
evolution of the dust in the sparse ISM in these galaxies.  The
results will help assess the possibility that these are elliptical
galaxies with cold gas and dust and (subsequent) star formation.