Variability of the SiO thermal line emission toward the young L1448-mm outflow

TL;DR

This study presents high-resolution observations of SiO emission in the L1448-mm outflow, revealing variability likely caused by young C-shocks, and identifies potential signatures of shock precursors at low velocities.

Contribution

It provides the first high-resolution, multi-epoch imaging of SiO emission showing variability and potential shock precursor signatures in a young outflow.

Findings

SiO emission shows variability over years in the outflow.

Narrow, faint SiO components are detected at low velocities, possibly indicating shock precursors.

SiO features are associated with young C-shocks and bow-shock morphologies.

Abstract

The detection of narrow SiO thermal emission toward young outflows has been proposed to be a signature of the magnetic precursor of C-shocks. Recent modeling of the SiO emission across C-shocks predicts variations in the SiO line intensity and line shape at the precursor and intermediate-velocity regimes in only few years. We present high-angular resolution (3.8"x3.3") images of the thermal SiO J=2-1 emission toward the L1448-mm outflow in two epochs (November 2004-February 2005, March-April 2009). Several SiO condensations have appeared at intermediate velocities (20-50 km/s) toward the red-shifted lobe of the outflow since 2005. Toward one of the condensations (clump D), systematic differences of the dirty beams between 2005 and 2009 could be responsible for the SiO variability. At higher velocities (50-80 km/s), SiO could also have experienced changes in its intensity. We propose that the SiO variability toward L1448-mm is due to a real SiO enhancement by young C-shocks at the internal working surface between the jet and the ambient gas. For the precursor regime (5.2-9.2 km/s), several narrow and faint SiO components are detected. Narrow SiO tends to be compact, transient and shows elongated (bow-shock) morphologies perpendicular to the jet. We speculate that these features are associated with the precursor of C-shocks appearing at the interface of the new SiO components seen at intermediate velocities.