The star formation history in the interacting galaxies NGC 4490 and 4485

We present the results of radio continuum observations of the interacting galaxies NGC 4490 and 4485, Observations have been made in the B-, C- and D-array configurations of the VLA at 1.49, 4.86 and 8.44 GHz, and with the Ryle Telescope at 15.2 GHz. The radio continuum maps have been fitted with a model spectrum consisting of an aged synchrotron and a thermal component, and have been decomposed into maps of each component. We find that the data are consistent with a high, ongoing star formation rate over the entire disc of NGC 4490, and that the electron age across NGC 4490 is consistent with a scenario in which NGC 4490 has been undergoing star formation at a constant rate for at least 10(8) yr, Combined with other evidence, we suggest that NGC 4490 is a young galaxy with an age of approximately 2 x 10(9) yr, and that it has had an approximately constant star formation rate during this period equal to the current rate of similar to 4.7 M-circle dot yr(-1). Furthermore, the effects of the interaction have not had sufficient time to affect the star formation rate in NGC 4490 significantly, although NGC 4485 has been severely affected by the interaction.