The interstellar medium and the massive stellar content towards the SNR G18.1-0.1 and neighbouring H II regions

Abstract

We perform a multiwavelength study of the SNR G18.1-0.1 and nearby several H II regions (infrared dust bubbles N21 and N22, and the H II regions G018.149-00.283 and G18.197-00.181). Our goal is to provide observational evidence supporting the view that massive stars are usually born in clusters from the same molecular cloud, which then produce, along their evolution, different neighbouring objects such as H II regions, interstellar bubbles and supernova remnants (SNRs). We suggest that the objects analysed in this work belong to a same complex located at the distance of about 4 kpc. Using molecular data we inspected the interstellar medium towards this complex and from optical and X-ray observations we looked for OB-type stars in the region. Analysing public 13 CO J = 1-0 data we found several molecular structures very likely related to the H II region/SNR complex. We suggest that the molecular gas is very likely being swept and shaped by the expansion of the H II regions. From spectroscopic optical observations obtained with the 2.15-m telescope at CASLEO, Argentina, we discovered three O-type stars very likely exciting the bubbles N21 and N22, and an uncatalogued H II region northwards of bubble N22, respectively. Also we found four B0-5 stars, one towards the bubble N22 and the others within the H II region G18.149-0.283. By inspecting the Chandra Source Catalogue we found two-point X-ray sources and suggest that one of them is an early O-type star. Finally, we inspected the large-scale interstellar medium around this region. We discovered a big molecular shell of about 70 × 28 pc in which the analysed complex appears to be located in its southern border.