High resolution observations of the 6cm H2CO maser in NGC 6240

We present high resolution ( ～1″) H2CO maser and 5GHz radio continuum observations toward nearby merging galaxy NGC 6240 made with the Very Large Array in an A configuration. Two concentrations of H2CO emission at about a 6σ level have been detected, one of which is associated with the strongest CO peak in the over-lap region while the other is about 2″ southwest of the southern galaxy. Both H2CO concentrations are associated with near infrared H2 emission, which is thought to be from shocked molecular gas. The total H2CO line luminosity in NGC 6240 is about 60% of that in Arp 220. Based on the distribution of H2CO emission in NGC 6240, which has both active galactic nuclei and an extreme starburst, the H2CO megamaser is likely to be related to the effect of the starburst instead of nuclear activity. Radio continuum cannot be the inversion mechanism of H2CO megamasers, because the two H2CO concentrations in NGC6240 are not associated with radio continuum emission. Instead, with the association of near infrared H2 emission, shock dynamics may produce the inverted population of H2CO needed to generate megamasers.