Spitzer Space Telescope - Guaranteed Time Observer Proposal #40448


Deep imaging of rich clusters in W5

Principal Investigator: Giovanni Fazio
           Institution: Smithsonian Astrophysical Observatory

     Technical Contact: Xavier Koenig, Harvard-SAO

Co-Investigators: 
Xavier Koenig, Harvard-Smithsonian Center for Astrophysics            
Lori Allen, Smithsonian Astrophysical Observatory                     
Joseph Hora, SAO                                                      

Science Category: star formation 
 Observing Modes: IracMap 
  Hours Approved: 10.7 

Abstract:
W5 is part of the well-known chain of large HII regions in the Perseus arm,
W3/W4/W5; however it is well segregated from W3/W4. At a distance of 2 kpc, W5
is comprised of multiple overlapping bubbles of ionized gas, extending over 2 x
1.5 degrees on the sky. We have recently uncovered previously unknown dense
clusters surrounding massive O stars in the interior of the W5 star forming
region with IRAC and MIPS observations. We propose to obtain deep images of
these clusters with IRAC in an effort to improve both the signal to noise of the
stars we detect in these clusters, and the spatial resolution of our
observations. This will help us to compare more directly with our near-IR and
optical data for the same dense clusters, and better understand their mass
functions and ages. This in turn will enable us to measure more accurately the
age sequence of star clusters across all of W5 and understand if triggering is a
possible mechanism to explain this sequence. The proposed observations will
improve the sensitivity of our existing IRAC observations by a factor of 4.