The filament IRDC G035.39–00.33 in the W48 molecular complex is one of the darkest infrared clouds observed by Spitzer .
It has been observed by the PACS ( 70 and 160 \mu m ) and SPIRE ( 250 , 350 , and 500 \mu m ) cameras of the Herschel Space Observatory as part of the W48 molecular cloud complex in the framework of the HOBYS key programme .
The observations reveal a sample of 28 compact sources ( deconvolved FWHM sizes < 0.3 pc ) complete down to \sim 5 ~ { } \mbox { $M _ { \odot } $ } in G035.39–00.33 and its surroundings .
Among them , 13 compact sources are massive dense cores with masses > 20 ~ { } \mbox { $M _ { \odot } $ } .
The cloud characteristics we derive from the analysis of their spectral energy distributions are masses of 20 - 50 ~ { } \mbox { $M _ { \odot } $ } , sizes of 0.1–0.2 pc , and average densities of 2 - 20 \times 10 ^ { 5 } ~ { } \mbox { $ \mbox { cm } ^ { -3 } $ } , which make these massive dense cores excellent candidates to form intermediate- to high-mass stars .
Most of the massive dense cores are located inside the G035.39–00.33 ridge and host IR-quiet high-mass protostars .
The large number of protostars found in this filament suggests that we are witnessing a mini-burst of star formation with an efficiency of \sim 15 \% and a rate density of \sim 40 ~ { } \mbox { $M _ { \odot } $ } yr ^ { -1 } kpc ^ { -2 } within \sim 8 pc ^ { 2 } , a large area covering the full ridge .
Part of the extended SiO emission observed towards G035.39–00.33 is not associated with obvious protostars and may originate from low-velocity shocks within converging flows , as advocated by previous studies .