HH 1158: The lowest luminosity externally irradiated Herbig-Haro jet

TL;DR

HH 1158 is the faintest externally irradiated Herbig-Haro jet discovered, providing insights into very low-luminosity jet physics and the effects of external irradiation in star-forming regions.

Contribution

This study reports the discovery and detailed analysis of the lowest luminosity externally irradiated HH jet, HH 1158, expanding understanding of jet properties at the faint end.

Findings

HH 1158 has a mass outflow rate of approximately 5.2 x 10^(-10) Msun/yr.

The jet shows asymmetries in brightness, morphology, and velocity between lobes.

Properties of HH 1158 are similar to other irradiated jets in sigma Orionis.

Abstract

We have identified a new externally irradiated Herbig-Haro (HH) jet, HH 1158, within ~2 pc of the massive OB type stars in the sigma Orionis cluster. At an Lbol ~ 0.1 Lsun, HH 1158 is the lowest luminosity irradiated HH jet identified to date in any cluster. Results from the analysis of high-resolution optical spectra indicate asymmetries in the brightness, morphology, electron density, velocity, and the mass outflow rates for the blue and red-shifted lobes. We constrain the position angle of the HH 1158 jet at 102+/-5 degree. The mass outflow rate and the mean accretion rate for HH 1158 using multiple diagnostics are estimated to be (5.2 +/- 2.6) x 10^(-10) Msun/yr and (3.0 +/- 1.0) x 10^(-10) Msun/yr, respectively. The properties for HH 1158 are notably similar to the externally irradiated HH 444 -- HH 447 jets previously identified in sigma Orionis. In particular, the morphology is such that the weaker jet beam is tilted towards the massive stars, indicating a higher extent of photo-evaporation. The high value for the Halpha/[SII] ratio is also consistent with the ratios measured in other irradiated jets, including HH 444 -- HH 447. The presence of an extended collimated jet that is bipolar and the evidence of shocked emission knots make HH 1158 the first unique case of irradiated HH jets at the very low-luminosity end, and provides an opportunity to learn the physical properties of very faint HH jet sources.