MERLIN and VLA observations of VII Zw 19: Distant cousin of M82

We have observed the starburst dwarf galaxy VII Zw 19 at subarcsecond resolution with MERLIN and MERLIN+European VLBI Network (EVN) at 18 cm, with MERLIN at 6 cm, and with the Very Large Array (VLA) in the A configuration at 6 and 2 cm. The galaxy is detected at all VLA wavelengths and is resolved. It is also resolved at 18 cm by MERLIN but is not detected by the EVN or by MERLIN at 6 cm. VII Zw 19 has a complex structure of nonthermal radio emission at 18 cm extended over ∼1200-1800 pc (4″-6″). That the EVN did not detect this emission indicates that there are no obvious point sources that could be radio supernovae. The 2 cm emission, predominantly thermal free-free emission, has a markedly different spatial distribution from the nonthermal emission. The radio colors show that the galaxy contains numerous supernova remnants, as well as many young H II regions, many of which are optically thick at 6 cm. Two extended regions of 2 cm emission have little 18 cm flux and are probably emission from young star clusters. VII Zw 19 resembles M82 in its radio and infrared spectrum, but the starburst region in VII Zw 19 is twice the size of the one in M82 and twice as luminous.