VLT integral field spectroscopy of embedded protostars : using near-infrared emission lines as tracers of accretion and outflow

Abstract

Aims. We present near-infrared spectroscopy of the forbidden emission line (FEL) and molecular hydrogen emission line (MHEL) regions at the bases of Herbig-Haro (HH) jets from seven embedded protostars: SVS 13 (the HH 7-11 progenitor), HH 26-IRS, HH 34-IRS, HH 72-IRS, HH 83-IRS, HH 300-IRS (IRAS 04239+2436) and HH 999-IRS (IRAS 06047-1117) Methods. The integral field spectrograph, SINFONI, on the European Southern Observatory’s Very Large Telescope (VLT) was used to characterise jet parameters in these formative regions, where the jets are collimated and accelerated. Results. We find considerable differences in the spectra of HH 83-IRS when compared to the other six sources; CO bandhead and atomic permitted lines from Ca i, Na i, Mg i and Al i are observed in emission in all but HH 83-IRS, where they are detected in absorption. It is likely that this source is more evolved than the others (or at the very least considerably less active). Strong CO bandhead emission is also detected in emission in the other six sources, while extended H2 ro-vibrational and [Fe ii] forbidden emission lines trace the outflows (only the HH jet from HH 83-IRS is undetected). CO bandhead and Brγ emission peaks are in most cases coincident with the jet source continuum position, consistent with excitation in an accretion disk or accretion flow. However, in the closest source, HH 300-IRS, we do find evidence for excitation in the outflow: here the emission peak is offset by 3.6(±0.7) AU along the flow axis. We also note a correlation between CO and Mg i, Na i and Ca i intensities, which supports the idea that these atomic permitted lines are associated with accretion disks. From H2 and [Fe ii] images we measure jet widths and derive upper limits to flow component opening angles. Although we do not find that the ionised [Fe ii] component is consistently narrower than the H2 flow component, we do find that narrower H2 and/or [Fe ii] flow components are associated with higher radial velocities (as reported in the literature). Flow opening angles, over the first few hundred AU in each source, are measured to be in the range 21°–42° in both H2 and [Fe ii]. Finally, from our 3-D data we are also able to map the extinction and electron density at the base of the outflows from some of our targets: within a few hundred AU, both decrease sharply with distance from the source. Conclusions. It seems clear that collimated atomic and molecular jets, which may initially exhibit a wide opening angle, are a feature of outflows from Class I protostars, Class II T Tauri stars, and possibly even Class 0 sources, and that these jets can be traced to within a few hundred AU of the driving source. A common jet collimation and acceleration mechanism seems inescapable for all stages of low mass star formation.