Discussing the distance bias in the estimation of Hi-GAL compact source physical properties – II. Evolutionary status and star formation rate

The derivation of the evolutionary stage and rate of star formation of star-forming sites from Galactic single-dish far-infrared and submillimetre surveys suffers from the relatively limited spatial resolution that prevents access to 'core' scales (r <= 0.1 pc) for heliocentric distances d greater than or similar to 1 kpc. In a previous article, we studied the implications of this 'distance bias' for the mass-radius relationship and its ability to diagnose potential sites for high-mass star formation, using a method that simulates the appearance at large distances of nearby and well-resolved star-forming regions mapped with Herschel. In the present article, we use the same method to quantify the bias introduced in the estimate of the evolutionary stage of dense 'clumps' (r >= 0.1 pc) revealed from the Herschel Hi-GAL survey, focusing in particular on the Lbol/Menv ratio, which is widely used as an evolutionary indicator. Furthermore, we discuss how the star formation rate (SFR) and efficiency (SFE) change with distance. The location of sources extracted from the virtual distance-displaced maps in the L-bol versus M-env diagram provides evolutionary indications that are consistent with those derived from the underlying population of cores and do not fluctuate substantially with distance. We also show that estimates of the SFR from integrated clump properties are consistent with estimates from the underlying resolved source population and show only minor variations with virtual distance. We conclude that methodologies commonly used to infer evolutionary indicators from clump-integrated quantities from large-scale single-dish Galactic far-infrared and submillimetre surveys are robust against distance and angular-resolution bias.