Spitzer Space Telescope - General Observer Proposal #80194


Rings of Fire: A Spitzer IRAC Study of Polar Ring Galaxies

Principal Investigator: Varsha  Kulkarni
           Institution: Univ. of South Carolina

     Technical Contact: Varsha  Kulkarni, Univ. of South Carolina

Co-Investigators: 
Monique C. Aller, University of South Carolina                        
Sarah J. U. Higdon, Georgia Southern University                       
James L. Higdon, Georgia Southern University                          

Science Category: nearby galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 25.2 

Abstract:
Polar ring galaxies (PRGs) are visually spectacular objects, consisting of a
robustly star forming ring of gas, dust and stars orbiting a plane perpendicular
to the major axis of a central S0. Since the ring material experiences the
gravitational potential in the polar plane, PRGs offer unique probes of the
shapes of the dark matter halo. Furthermore, polar rings represent star forming
environments distinct from the disks of spiral galaxies and collisional ring
galaxies, where density waves act to collect the ISM and trigger star formation.
Many questions remain regarding the formation and evolution of PRGs: How old are
the polar rings? Are they formed through polar mergers or by mass accretion? Is
star formation the result of gravitational instabilities or stochastic
propagation? To answer these questions, it is important to determine properties
of the polar ring's stellar component. This requires observations in the
infrared where extinction is minimal and where evolved stellar populations are
most prominent. IRAC 3.6 and 4.5 micron imaging remains the best means of
probing the stellar structure of PRGs due to its high angular resolution and
sensitivity. We propose to obtain IRAC 3.6 and 4.5 micron images for a
comprehensive sample of PRGs, with the following goals (1) We will determine the
ring's stellar mass surface density, both directly and in concert with existing
UV and optical images. (2) We will estimate the ages of the rings. (3) Together
with available HI data, we will estimate the ring's gravitational stability, and
thus the dominant star formation trigger. (4) We will characterize extinction in
the polar ring sections ``back-lit'' by the central S0, and (5) We will better
constrain the Tully-Fisher relation for PRGs, and thus halo shapes. The proposed
data will give fresh insights into the dynamics and star formation histories of
PRGs, and the formation/evolution mechanisms of S0 galaxies. The Spitzer warm
mission offers the best chance to realize these goals.