SIMBAD references

Using the IRAM 30 m telescope, a mapping survey in optically thick and thin lines was performed toward 46 high-mass-star-forming regions. The sample includes UC H II precursors and UC H II regions. Seventeen sources are found to show ``blue profiles'', the expected signature of collapsing cores. The excess of sources with blue over red profiles [(N_blue-N_red)/N_total] is 29% in the HCO⁺ J=1-0 line, with a probability of 0.6% that this is caused by random fluctuations. UC H II regions show a higher excess (58%) than UC H II precursors (17%), indicating that material is still accreted after the onset of the UC H II phase. Similar differences in the excess of blue profiles as a function of evolutionary state are not observed in low-mass-star-forming regions. Thus, if confirmed for high-mass-star-forming sites, this would point to a fundamental difference between low- and high-mass-star formation. Possible explanations are inadequate thermalization, stronger influence of outflows in massive early cores, larger gas reserves around massive stellar objects, or different trigger mechanisms between low- and high-mass-star formation.