2008A&A...486..807A

We analyse the distribution of the molecular gas towards the region containing the open cluster Havlen-Moffat 1 (HM1) the Wolf-Rayet stars WR87, WR89, and WR91, and the star forming regions RCW 121 and RCW122, with the aim of looking for a possible physical relationship among these objects. We used the carbon monoxide observations carried out at λ∼2.6mm with the 4m NANTEN radiotelescope; new flux density determinations derived from already existing radio continuum surveys at 2.417, 5, 8.35, and 14.35GHz; continuum flux density determinations available in the literature; and the Midcourse Space Experiment (MSX) and the Improved Reprocessing of the IRAS Survey (IRIS) databases. Adopting a distance of 5kpc for RCW121 and RCW122, we found a giant molecular cloud (GMC) with a linear extent of ∼100x20pc to be associated with galactic star-forming regions. The total mass of this GMC is of the order of 1.2x10⁶ solar masses and its mean radial velocity is about -15km/s. Within the GMC there are individual molecular gas concentrations, having total molecular masses in the range from 4.6x10⁴M_☉ (RCW122C) to 2.2x10⁵M_☉ (RCW122). The CO profiles observed toward the peak of the molecular concentrations are broad, with typical full-width half-maximum around 6 to 7km/s, and show line asymmetries and/or double-peaked shape that change with the observed position within a given CO concentration. An analysis of the MSX and IRAS databases show that each CO concentration has a strong IR counterpart. The dust temperature of these concentrations range from 46K (RCW121) to 76K (RCW122C). Their infrared luminosity are a few times 10⁵L_☉. The new radio continuum flux density determinations are in good agreement with previous determinations at other frequencies, and confirm the thermal nature of RCW121 and RCW122. Based on the newly-determined 5GHz flux density, we found that to power these HII regions, each of them must harbour a sizable number of O type stars. Under the assumption that all the ionizing stars have a O7V spectral type, at least ∼8 and ∼4 of these stars would be needed to ionize RCW122 and RCW121, respectively.