SIMBAD references

We present observations of Arp 147, a galaxy system comprising a collisionally created ring galaxy and an early-type galaxy, using the Oxford SWIFT integral field spectrograph (IFS) at the 200-inch Hale telescope. We derive spatially resolved kinematics from the IFS data and use these to study the interaction between the two galaxies. We find the edge-to-edge expansion velocity of the ring is 225±8 km/s, implying an upper limit on the time-scale for the collision of 50 Myr. We also calculate that the angle of impact for the collision is between 33° and 54°, where 0° would imply a perpendicular collision. The ring galaxy is strongly star forming with the star formation likely to have been triggered by the collision between the two galaxies.

We also measure some key physical parameters in an integrated and spatially resolved manner for the ring galaxy. Using the observed B-I colours and the Hα equivalent widths, we conclude that two stellar components (a young and an old population) are required everywhere in the ring to simultaneously match both observed quantities. We are able to constrain the age range, light and mass fractions of the young star formation activity in the ring, finding a modest age range, a light fraction of less than a third, and a negligible (<1 per cent) mass fraction. We postulate that the redder colours observed in the south-east corner of the ring galaxy could correspond to the nuclear bulge of the original disc galaxy from which the ring was created, consistent with the stellar mass in the south-east quadrant being 30–50 per cent of the total. The ring appears to have been a typical disc galaxy prior to the encounter.

The ring shows electron densities consistent with typical values for star-forming H II regions. The eastern half of the ring exhibits a metallicity a factor of ∼ 2 higher than the western half. The ionization parameter, measured across the ring, roughly follows the previously observed trend with metallicity.