Spitzer Space Telescope - General Observer Proposal #60175


Spitzer Studies of X-ray Detected Radio Hotspots

Principal Investigator: Michael Werner
           Institution: JPL

     Technical Contact: Varoujan Gorjian, JPL

Co-Investigators: 
Dayton Jones, JPL                                                     
Charles Lawrence, JPL                                                 
David Meier, JPL                                                      
David Murphy, JPL                                                     
Anthony Readhead, Caltech                                             

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 24.2 

Abstract:
We propose new observations at 3.6um of 27 hotspots in the extended lobes of
radio galaxies which have also been detected in x-rays, which will be combined
with archival Spitzer data on 14 additional hotspots. The hotspots arise at the
interface where a jet accelerated by a black hole at the center of the galaxy
plows into the local intergalactic medium. Shocks created at this interface
accelerate electrons to relativistic energies, and synchrotron radiation from
the electrons produces both the radio hotspot and, as the electrons diffuse away
from the hotspot, the extended emission from the lobe. These hotspots play a
critical role in the transport of energy from the nuclei of galaxies back into
the intergalactic medium. However, our understanding of the complex and highly
non-linear interactions between relativistic jets and the IGM occurring in
hotspots is limited by the paucity of data in the critical region where the
interplay between the ageing of electron energy distributions and the beginning
of inverse Compton photons occurs. Spitzer's 3.6um band is right in the middle
of this critical region, with the required sensitivity. The new observations are
planned to distinguish between several models put forward for hotspots based on
radio and x-ray data alone. Spitzer observations are essential for understanding
these cosmic train wrecks where relativistic jets hit the IGM. No other existing
facility can come close to achieving the sub-uJy sensitivity needed to detect
the hotspots at 3.6um. Although our observing time request is modest, our
intention to produce a catalog of multispectral data on upwards of 40 hotspots
is consistent with Warm Spitzer's thrust towards comprehensive studies of
important astrophysical questions.