Spitzer Space Telescope - General Observer Proposal #60132


Enigmatic features in Centaurus A

Principal Investigator: Francesco Massaro
           Institution: Harvard-Smithsonian Astrophysical Observatory

     Technical Contact: Mark Birkinshaw, University of Bristol

Co-Investigators: 
Matt Ashby, Harvard-CfA                                               
Mark Birkinshaw, University of Bristol                                
Judith Croston, University of Hertfordshire                           
Dick Hunstead, University of Sydney                                   
Ralph Kraft, Harvard-CfA                                              
Christian Leipski, UC Santa Barbara                                   
Larry Rudnick, University of Minnesota                                
Howard Smith, Harvard-CfA                                             
Zhong Wang, Harvard-CfA                                               
Steve Willner, Harvard-CfA                                            
Diana Worrall, University of Bristol                                  

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 10.9 

Abstract:
Centaurus A is the closest radio-bright active galaxy, and provides a detailed
view of the physics of radio sources and their interaction with the surrounding
interstellar and intergalactic gas. In our recent X-ray based work on Centaurus
A we have found two surprising new results: that the shock feature around the
inner SW radio lobe is a synchrotron rather than thermal gas structure; and that
the northern jet generates X-ray bright knots of thermal emission as it enters
the northern middle lobe. In these knots we see some evidence for associated
star clusters. These unexpected discoveries have important implications for
source physics. The broad-band energy output of the X-ray shock traces the
population of relativistic particles and hence acceleration physics at the
shock. The knots are evidence of interaction of radio jets with interstellar
gas, and the subsequent injection of thermal matter into radio lobes. Here we
propose a single AOR that will make 1-hour exposures of the shock feature and
the X-ray bright knots in each band. This will constrain the spectral energy
distribution of the shock, and measure the IR properties of the dissipating gas
clouds and embedded stars in the X-ray knots, comparing the properties of these
clouds with HI clouds which appear not yet to have interacted with the jet.