2015A&A...582A..64L

With only a few low- and high-mass star-formation regions studied in detail so far, it is unclear what role the enviroment plays in complex molecule formation. In this light, a comparison of relative abundances of related species between sources might be useful for explaining any observed differences. We seek to measure the relative abundance between three important complex organic molecules, ethylene glycol ((CH₂OH)₂), glycolaldehyde (CH₂OHCHO) and methyl formate (HCOOCH₃), toward high-mass protostars and thereby provide additional constraints on their formation pathways. We use IRAM 30m single-dish observations of the three species toward two high-mass star-forming regions - W51/e2 and G34.3+0.2 - and report a tentative detection of (CH₂OH)₂ toward both sources. Assuming that (CH₂OH)₂, CH₂OHCHO, and HCOOCH₃ spatially coexist, relative abundance ratios, HCOOCH₃/(CH₂OH)₂, of 31 and 35 are derived for G34.3+0.2 and W51/e2, respectively. CH₂OHCHO is not detected, but the data provide lower limits to the HCOOCH₃/CH₂OHCHO abundance ratios of ≥193 for G34.3+0.2 and ≥550 for W51/e2. A comparison of these results to measurements from various sources in the literature indicates that the source luminosities may be correlated with the HCOOCH₃/(CH₂OH)₂ and HCOOCH₃/CH₂OHCHO ratios. This apparent correlation may be a consequence of the relative time scales each source spend at different temperature ranges in their evolution. Furthermore, we obtain lower limits to the ratio of (CH₂OH)₂/CH₂OHCHO for G34.3+0.2 (≥6) and W51/e2 (≥16). This result confirms that a high (CH₂OH)₂/CH₂OHCHO abundance ratio is not a specific property of comets, as previously speculated.