Spitzer Space Telescope - General Observer Proposal #50172


Spectroscopy of IR Galaxies Over The Merger Sequence

Principal Investigator: Carrie Bridge
           Institution: Spitzer Science Center

     Technical Contact: Carrie Bridge, Spitzer Science Center

Co-Investigators: 
Harry Teplitz, Spitzer Science Center                                 
Lee Armus, Spitzer Science Center                                     
Raymond Carlberg, University of Toronto                               
Chris Conselice, Univeristy of Nottingham                             
Phil Appleton, Spitzer Science Center                                 

Science Category: interacting/merging galaxies 
 Observing Modes: IrsStare 
  Hours Approved: 32.4 

Abstract:
Locally, ~50% of LIRGs and 95% of ULIRGs are driven by galaxy mergers, which
provide the primary means of triggering star formation and AGN activity.
However, at z>0.7 the dominate mechanisms responsible for the IR emission in
LIRG galaxies may be different from those locally, as only 30% of z=0.7 LIRGs
exhibit merger signatures and the remaining 70% appear to be undisturbed spiral
galaxies. Although the merger process itself is the same at both high and low
redshift, the galaxies involved in the mergers are not. At higher redshift,
galaxies have higher gas mass fractions, meaning more fuel for star formation
and AGN, can have smaller bulges, and are less likely to have bar structures.
These differences can affect the onset, strength and relative contribution to
their IR luminosity from starbursts and AGN. Using the CFHTLS-Deep Catalog of
Interacting Galaxies we have identified 24 (>1mJy at 24um) early to late stage
IR bright mergers, between 0.45<z<1.0, based on tidal signatures, for deep MIR
spectroscopy. Using Mid-IR spectral diagnostics, we will quantify the relative
IR contribution from star formation and AGN, the onset of these processes, and
how they compare to local analogs, all as a function of merger stage.