A Hi-GAL study of the high-mass star-forming region G29.96-0.02

Context. G29.96-0.02 is a high-mass star-forming cloud observed at 70, 160, 250, 350, and 500 mu m as part of the Herschel survey of the Galactic plane (Hi-GAL) during the science demonstration phase. Aims. We wish to conduct a far-infrared study of the sources associated with this star-forming region by estimating their physical properties and evolutionary stage, and investigating the clump mass function, the star formation efficiency and rate in the cloud. Methods. We have identified the Hi-GAL sources associated with the cloud, searched for possible counterparts at centimeter and infrared wavelengths, fitted their spectral energy distribution and estimated their physical parameters. Results. A total of 198 sources have been detected in all 5 Hi-GAL bands, 117 of which are associated with 24 mu m emission and 87 of which are not associated with 24 mu m emission. We called the former sources 24 mu m-bright and the latter ones 24 mu m-dark. The [70-160] color of the 24 mu m-dark sources is smaller than that of the 24 mu m-bright ones. The 24 mu m-dark sources have lower L-bol and L-bol/M-env than the 24 mu m-bright ones for similar M-env, which suggests that they are in an earlier evolutionary phase. The G29-SFR cloud is associated with 10 NVSS sources and with extended centimeter continuum emission well correlated with the 70 mu m emission. Most of the NVSS sources appear to be early B or late O-type stars. The most massive and luminous Hi-GAL sources in the cloud are located close to the G29-UC region, which suggests that there is a privileged area for massive star formation toward the center of the G29-SFR cloud. Almost all the Hi-GAL sources have masses well above the Jeans mass but only 5% have masses above the virial mass, which indicates that most of the sources are stable against gravitational collapse. The sources with M-env > M-virial and that should be undergoing collapse and forming stars are preferentially located at less than or similar to 4' of the G29-UC region, which is the most luminous source in the cloud. The overall SFE of the G29-SFR cloud ranges from 0.7 to 5%, and the SFR ranges from 0.001 to 0.008 M-circle dot yr(-1), consistent with the values estimated for Galactic HII regions. The mass spectrum of the sources with masses above 300 M-circle dot, well above the completeness limit, can be well-fitted with a power law of slope alpha = 2.15 +/- 0.30, consistent with the values obtained for the whole l = 30 degrees, associated with high-mass star formation, and l = 59 degrees, associated with low-to intermediate-mass star formation, Hi-GAL SDP fields.