Formaldehyde and OH in the Orion molecular clouds

Formaldehyde 6-cm absorption has been mapped in the Orion region using the Jodrell Bank MK II radio telescope (beamwidth 9 x 10 arcmin2). The measurements cover the Lynds dust clouds L1630, 1641 and part of 1647. Maps are presented of the formaldehyde line intensity and velocity over the region. The formaldehyde 6-cm line is found to be a good tracer of total gas density. The mass of molecular hydrogen implied by the measurements is 2 x 104 Msun for L1630 and 5 x 104 Msun for L1641 and 1647. The largest concentrations within the clouds have masses far in excess of their virial masses and are probably collapsing. Measurements have also been made of thermal emission from OH at 1667 MHz. 24 positions were observed with the Jodrell Bank MK IA radio telescope (beamwidth 10 arcmin). There is a good correlation between the OH and H2 CO line intensities. (author)