Radio-Continuum Emission in Polar-Ring Galaxies

We have used the Very Large Array aperture synthesis telescope to conduct a radio continuum survey of polar-ring galaxies, at 20 cm and 6 cm. Forty objects were observed at 20 cm with ≃ 5 resolution. Twenty (50%) of the program sources were detected at 20 cm, down to our 5-σ limit of 0.5 mJy beam−1. This detection rate is similar to those in surveys with comparable sensitivity for early-type galaxies without polar rings. Sixteen of the objects we detected at 20 cm were also observed at 6 cm. We show radio continuum maps for the five objects in our sample that have noticeably extended emission. Our spatial resolution was sufficient to distinguish between emission originating in the host galaxy from that in the polar ring. The radio morphology of the extended sources, as well as the radio to far-infrared flux ratio and the radio spectral indices of our detected sources, indicate that star formation, not nuclear activity, is the dominant source of the radio continuum emission in polar-ring galaxies. However, the implied star-formation rates are modest, and only one of our sample galaxies will consume its supply of cool gas within 500Myr. Subject headings: galaxies: elliptical and lenticular, galaxies: interactions, galaxies: peculiar, radio continuum 1. Background & Motivation Polar ring galaxies (PRG’s) are early-type galaxies with rings of gas, stars, and dust that orbit nearly perpendicular to the equatorial plane of the central galaxy. It is generally assumed that they result from an accretion or merger event that occurred some time after the host galaxy formed (Schweizer et al. 1983; Whitmore et al. 1990, hereafter PRC). Objects that have undergone a 1 Department of Physics & Astronomy, Beloit College, 700 College Street, Beloit, WI 53511-5595 2 Astronomy Department, University of Wisconsin – Madison, 475 N. Charter St., Madison, WI 53706