The origin of the molecular emission around the southern hemisphere Re 4 IRS – HH 188 region

Context. We present SEST observations of the molecular environment ahead of the southern Herbig-Haro object 188 (HH 188), associated with the low-mass protostar Re 4 IRS. We have also used the SuperCosmos Hα survey to search for Hα emission associated with the Re 4 IRS – HH 188 region. Aims. The aim of the present work is to study the properties of the molecular gas and to better characterize this southern star forming region. Methods. We mapped the HCO 3–2 and HCO 1–0 emission around the YSO and took spectra of the CH3OH 20–10 A + and 2−1–1−1 E and SO 65–54 towards the central source. Column densities are derived and different scenarios are considered to explain the origin of the molecular emission. Results. HCO arises from a relatively compact region around the YSO; however, its peak emission is displaced to the south following the outflow direction. Our chemical analysis indicates that a plausible scenario is that most of the emission arises from the cold, illuminated dense gas ahead of the HH 188 object. We have also found that HH 188, a high excitation object, seems to be part of a parsec scale and highly collimated HH system. Re 4 IRS is probably a binary protostellar system, in the late Class 0 or Class I phase. One of the protostars, invisible in the near-IR, seems to power the HH 188 system.