Spitzer Space Telescope - General Observer Proposal #50326


Direct Physical Diagnostics of Triggered Star Formation

Principal Investigator: Crystal Brogan
           Institution: National Radio Astronomy Observatory (NRAO)

     Technical Contact: Crystal Brogan, National Radio Astronomy Observatory (NRAO)

Co-Investigators: 
Remy Indebetouw, University of Virginia                               
Claudia Cyganowski, University of Wisconsin                           
Ed Churchwell, University of Wisconsin                                
Mark Wolfire, University of Maryland                                  
Barbara Whitney, Space Science Institute                              
Christer Watson, Manchester College                                   

Science Category: star formation 
 Observing Modes: IrsMap 
  Hours Approved: 14.8 

Abstract:
We propose to combine the unique spectroscopic capabilities of Spitzer IRS and
the VLA to study possible instances of triggered star formation using a more
comprehensive range of diagnostics than ever before. This study is essential to
move beyond morphological and photometric color arguments (e.g. the spatial
distribution of red sources) for triggered star formation. In particular,
Spitzer IRS data will allow us to (I) Determine the ionized gas properties via
comprehensive photoionization modeling of the HII region; (II) Perform detailed
modeling of the PDR including penetration of UV radiation and heating; (III)
Locate and model shocks that may be compressing gas in the triggering zone; and
(IV) Tightly constrain the nature and evolutionary state of embedded sources in
the rim to see if their age and the distribution of circumstellar material is
consistent with formation by triggering. Together with VLA ammonia data
(proposed separately) these Spitzer IRS diagnostics will allow us to
conclusively determine the nature of the triggering forces (ionized gas pressure
and shocks), conditions in the triggered molecular gas, and the natures of the
putatively triggered protostars. Moreover, by providing a complete picture of
the physical conditions in the ionized, PDR, and molecular gas, these data offer
the best chance to date to distinguish between the leading theories for HII
region triggering: collect-and-collapse and radiation driven implosion.