Speaker
Description
Ring galaxies (RiGs) represent a particularly favorable environment for the formation of Ultra Luminous X-ray sources (ULXs). These systems are produced by a cosmic crash between a disk galaxy and a smaller companion, generating an expanding density wave that compresses the interstellar medium and triggers intense star formation along a ring. The archetypal Cartwheel galaxy and several other well known RiGs host unusually large populations of ULXs, suggesting that the physical conditions created by these collisions may enhance the production of the most luminous X-ray binaries.
Previous studies of a small sample of X-ray bright RiGs revealed an X-ray luminosity function flatter than that observed in more heterogeneous galaxy samples, indicating either a larger number of ULXs or the presence of a brighter population of binaries. However, these galaxies were selected among the most spectacular and actively star-forming systems, raising the question of whether they are representative of the RiGs population as a whole
To address this issue, we have assembled the first complete sample of nearby ring galaxies (up to D <= 70 Mpc) from the Arp&Madore sample, and obtained a combination of archival and new observations. Our program includes Chandra X-ray observations to identify and characterize ULX populations, complemented by optical imaging and spectroscopy from SOAR to investigate the stellar populations, star formation history, and metallicity of the rings. Recent results indicate that the rings host very young stellar populations and lower metallicities than the central regions of their parent galaxies, conditions that are thought to favor ULX formation.
We present the complete sample, describe the multiwavelength dataset, and report preliminary results on the ULX content of these systems. We compare the properties of the complete sample with those of the previously studied X-ray bright ring galaxies and with other star-forming galaxies, testing whether the presence of a ring alone is a tell-tale sign of an extreme ULX populations or whether additional factors are required.