Ammonia absorption toward the ultracompact HII regions G45.12+0.13 and G45.47+0.05

We present observations of the 1.3 cm continuum and NH3(2,2) and (4,4) inve rsion lines toward the two ultracompact H II regions G45.12+0.13 and G45.47 +0.05 with a resolution of about 3 ". In G45.12+0.13 we find that the conti nuum emission from the ultracompact core is embedded in a larger region wit h an extent of about 20 " x 10 ". Compact absorption in the NH3(2,2) and (4 ,4) lines is detected against the bright continuum core. The ammonia data i ndicate T-rot = 78 K and N(NH3) = 1.4 x 10(16) cm(-2). The molecular gas tr aced by the NH3 absorption is blueshifted by about 5 km s(-1) with respect to the ionized gas and the bulk of the molecular gas in the region. Possibl y the ammonia absorption traces the molecular gas at the base of an outflow which originates very close to the ultracompact H II region. In the case of G45.47+0.05, we measure a deconvolved size of 1." 5 x 0." 8 for the region of 1.3 cm continuum emission. We detect extended emission in the NH3(2,2) line in the vicinity of the ionized gas. Compact absorption i s detected in both the (2,2) and (4,4) line against the 1.3 cm continuum. T he absorption line data indicate T-rot = 59 K and N(NH3) = 1.8 x 10(17) cm( -2). The ammonia absorption occurs at a velocity redshifted by about 3.5 km s(-1) with respect to the emission. This supports the hypothesis of a remn ant infalling molecular core onto the ultracompact H II region.