SiO outflows in high-mass star forming regions: A potential chemical clock?

TL;DR

This study investigates SiO outflows in high-mass star-forming regions, revealing that jet activity decreases over time and proposing SiO emission as a potential chemical clock for evolutionary stages.

Contribution

It provides the first clear evidence of declining SiO outflow luminosity with evolution in high-mass star-forming regions, using a homogeneous sample.

Findings

88% of sources show SiO emission indicating active star formation.

SiO luminosity decreases with increasing L/M ratio, suggesting jet activity declines over time.

Minor changes observed in SiO(3-2) to SiO(2-1) intensity ratio across evolutionary stages.

Abstract

Some theoretical models propose that O-B stars form via accretion, in a similar fashion to low-mass stars. Jet-driven molecular outflows play an important role in this scenario, and their study can help to understand the process of high-mass star formation and the different evolutionary phases involved. Observations towards low-mass protostars so far favour an evolutionary picture in which jets are always associated with Class 0 objects while more evolved Class I/II objects show less evidence of powerful jets. The present study aims at checking whether an analogous picture can be found in the high-mass case. The IRAM 30-m telescope (Spain) has been used to perform single-pointing SiO(2-1) and (3-2) observations towards a sample of 57 high-mass molecular clumps in different evolutionary stages. Continuum data at different wavelengths, from mid-IR to 1.2 mm, have been gathered to build the spectral energy distributions of all the clumps and estimate their bolometric luminosities. SiO emission at high velocities, characteristic of molecular jets, is detected in 88% of our sources, a very high detection rate indicating that there is ongoing star formation activity in most of the sources of our sample. The SiO(2-1) luminosity drops with L/M, which suggests that jet activity declines as time evolves. This represents the first clear evidence of a decrease of SiO outflow luminosity with time in a homogeneous sample of high-mass molecular clumps in different evolutionary stages. The SiO(3-2) to SiO(2-1) integrated intensity ratio shows only minor changes with evolutionary state.