Abstract The 110 -111 formaldehyde (H2CO) absorption line and H110α radio recom bination line (H RRL) are observed towards the giant HII region in cloud complex W43. The observations are obtained using the Nanshan 25 m single dish operated by Urumqi Observatory, National Astronomical Observatories of China. A region about 30'×30' is observed, which covers the whole HII region in W43. Except for the central 10' region, all the other seven points are first observed with the H2CO 110 - 111 absorption. The column density of the H2CO is calculated, and the H2CO density contours show some differences with the infrared image. Multiple features appear in the H2CO and H RRL which indicate complex structure. The intensities of the H2CO and the velocities of the H110α seem to present a linear correlation, which illustrates that the sphere of influence of the central WR/OB cluster may be much more extended than presently known, since the size is nearly 50 pc.

Keywords ISM: radio lines — HII regions — stars: formation

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