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

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: mbeltran@arcetri.astro.it
² University of Puerto Rico, Río Piedras Campus, Physics Dept., Box 23343, UPR station, San Juan, Puerto Rico, USA
³ INAF – Istituto di Astrofisica e Planetologia Spaziali, via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁴ Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ ESO, Karl Schwarzschild str. 2, 85748 Garching, Germany
⁷ Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK

Received: 11 January 2013
Accepted: 18 February 2013

Abstract

Context. G29.96−0.02 is a high-mass star-forming cloud observed at 70, 160, 250, 350, and 500 μm 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 μm emission and 87 of which are not associated with 24 μm emission. We called the former sources 24 μm-bright and the latter ones 24 μm-dark. The [70–160] color of the 24 μm-dark sources is smaller than that of the 24 μm-bright ones. The 24 μm-dark sources have lower L_bol and L_bol/M_env than the 24 μm-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 μm 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  ≲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_⊙ yr^-1, consistent with the values estimated for Galactic Hii regions. The mass spectrum of the sources with masses above 300   M_⊙, well above the completeness limit, can be well-fitted with a power law of slope α = 2.15 ± 0.30, consistent with the values obtained for the whole l = 30°, associated with high-mass star formation, and l = 59°, associated with low- to intermediate-mass star formation, Hi-GAL SDP fields.