On the Structure and Star Formation within Polar Ring Galaxies

Polar Ring Galaxies (PRGs) consist of a robustly star-forming ring of gas, dust and stars orbiting in a plane perpendicular to the major axis of a central host galaxy. Many questions remain regarding the formation and evolution of PRGs: How old are the polar rings? Are they formed through galaxies colliding or by mass accretion? Is the star formation a result of gravitational instabilities or stochastic propagation? To begin answering these questions, we have assembled a set of PRGs observed in infrared wavelengths by the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope (SST), as part of the Spitzer Warm Mission to collect 3.6- and 4.5-micron imaging. These two wavebands are accompanied by corresponding optical imaging data gathered with Hubble Space Telescope, Sloan Digital Sky Survey, and Gemini-South Observatory, in addition to HI radio data where available. We describe processing of the IRAC images and GALFIT analysis to produce structural models, enabling us to ascertain light profiles and morphological characteristics of specific target galaxies. The two infrared mosaics of each galaxy - one for each waveband - were compared to obtain dust extinction maps for the rings and host galaxies. The information collected from these procedures - structural modeling, photometry, and color map construction - are being used to (1) construct surface-brightness profiles for the galaxies, (2) draw comparisons between these structural models and previous model predictions, (3) construct spectral energy distributions of the rings, (4) determine star formation rates, stellar masses, and ages for the rings, and (5) determine the distribution of dust within the ring via extinction maps. This work was funded in part by a NASA South Carolina Space Grant Consortium Graduate Research Assistantship, and by a grant from the NASA Spitzer Science Center.