tokens: CO(3–2) and HCO(4–3) lines with the ASTE telescope, aiming at studying in detail the spatial distribution and physical characteristics of the molecular gas associated with the nebula. To analyze the properties of the dust in the nebula and its surroundings we use images from the ATLASGAL and Herschel databases. To account for the interaction between the ionized and molecular gas and to determine the evolutionary status of the H ii region, we use radio continuum data from the NVSS archives. This analysis also allows us to identify spots of dense molecular gas and dust where the massive star formation is developing, particularly the central region corresponding to the source IRAS 18139-1842, where star formation processes seem to be very active. In addition, we look for signatures of star formation in the surroundings using archival photometric data and we investigate a probable scenario of triggered star formation at the border of the nebula. We also study the characteristics of an identified stellar cluster projected onto the border of the bubble using new IR data. This provides some additional information that helps us to better understand the star formation activity in the nebula. N5 is an open IR bubble of about 8 in diameter centered at RA, Dec(J2000) = 181702, 184019, coincident with the H ii region Sh2-39, and located at a distance of 4.1 kpc ( Bronfman et al. 1996 ; Faúndez et al. 2004 ). In Fig. 1 we present a 8.28 m (MSX-A) emission image of the nebula, which has a typical arc-shaped morphology in the mid-IR wavelengths. At wavelengths of about 8 m most of the emission originates in strong features of PAH molecules, which are considered to be good tracers of warm UV-irradiated photodissociation regions (PDR; Hollenbach Tielens 1997 ). Since these complex molecules are destroyed inside the ionized gas of an H ii region, they indicate the limits of the ionization front and delineate the boundaries of the bubble nebula, giving a glimmer of the location of the parental molecular gas against which N5 is likely expanding. The open morphology of the IR nebula suggests that Sh2-39 is the classical H ii region density bounded toward the outer side (eastward) and ionization bounded toward the molecular cloud (westward). The nebula is believed to be linked to the IR sources IRAS 18139-1842 and IRAS 18139-1839, which both have characteristics of massive young stellar objects (see Sect. 6). The CS(2–1)line was detected by Bronfman et al. (1996) at a velocity 1 of 40.2 km s in the direction of IRAS 18139-1842. NH line and HO maser emission, which are believed to be excellent indicators of early stages of massive star formation, were also detected toward this IRAS source ( Sunada et al. 2007 ; Urquhart et al. 2011 ), while radio recombination line observations (H87 and H88) show emission at the same position at a velocity of 41 km s (Lockman, 1989 , see Fig. 1 ), which indicates the existence of high density ionized gas at the same radial velocity
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