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Unveiling Ionized Jet Morphologies: Sub-arcsecond VLA Observations of Compact Radio Sources

Tatiana M. Rodriguez, Peter Hofner, Emmanuel Momjian, Esteban D. Araya, Ananay Sethi, Viviana Rosero

TL;DR

High-mass star formation jets are often obscured by dense envelopes; this study uses high-resolution VLA observations to directly probe ionized jets in 23 candidate regions. It finds three morphologies, widespread H2O masers near the continuum peaks, and measurable proper motions consistent with collimated outflows. The data favor shock ionization as the main jet mechanism and reveal core/halo shock structures, with seven sources classified as thermal jets and sixteen as ionized jets.

Abstract

We present sub-arcsecond ($θ\sim0.1^{\prime\prime}$) resolution VLA 1.3 cm continuum and 22.2 GHz H$_2$O maser observations toward 15 compact radio continuum sources with rising spectral index and 8 string-like radio continuum structures in the Rosero et al. (2016, 2019) survey. Three different morphologies are observed: elongated or double-peak string-like structure (6 out of 23 cases), a collection of distinct continuum peaks (4 out of 23 cases), and single compact sources (13 out of 23 cases). The majority of H$_2$O maser spots detected are within a sky-projected distance of $\sim5,000$ au from the radio continuum peaks and tend to be well aligned and distributed in an elongated structure when more than three spots are observed. We generally recover less emission than Rosero et al. (2016, 2019), which together with the fact that more than half of the jet candidates in our survey appear mostly compact, suggest core/halo shock structures even on small scales. We also detected proper motion in 10 cases and measured an average projected velocity of approximately 120 km s$^{-1}$. Radio brightness variability is detected in at least two cases, possibly due to weak accretion bursts. This work, together with our previous molecular jet study, provides further evidence that support the main source of ionization in the studied sources is shocks, yet collimation is only observed in 4 cases. We conclude that the available data supports the thermal jet classification of 7 sources, and the ionized jet interpretation is further supported in 16 sources.

Unveiling Ionized Jet Morphologies: Sub-arcsecond VLA Observations of Compact Radio Sources

TL;DR

High-mass star formation jets are often obscured by dense envelopes; this study uses high-resolution VLA observations to directly probe ionized jets in 23 candidate regions. It finds three morphologies, widespread H2O masers near the continuum peaks, and measurable proper motions consistent with collimated outflows. The data favor shock ionization as the main jet mechanism and reveal core/halo shock structures, with seven sources classified as thermal jets and sixteen as ionized jets.

Abstract

We present sub-arcsecond () resolution VLA 1.3 cm continuum and 22.2 GHz HO maser observations toward 15 compact radio continuum sources with rising spectral index and 8 string-like radio continuum structures in the Rosero et al. (2016, 2019) survey. Three different morphologies are observed: elongated or double-peak string-like structure (6 out of 23 cases), a collection of distinct continuum peaks (4 out of 23 cases), and single compact sources (13 out of 23 cases). The majority of HO maser spots detected are within a sky-projected distance of au from the radio continuum peaks and tend to be well aligned and distributed in an elongated structure when more than three spots are observed. We generally recover less emission than Rosero et al. (2016, 2019), which together with the fact that more than half of the jet candidates in our survey appear mostly compact, suggest core/halo shock structures even on small scales. We also detected proper motion in 10 cases and measured an average projected velocity of approximately 120 km s. Radio brightness variability is detected in at least two cases, possibly due to weak accretion bursts. This work, together with our previous molecular jet study, provides further evidence that support the main source of ionization in the studied sources is shocks, yet collimation is only observed in 4 cases. We conclude that the available data supports the thermal jet classification of 7 sources, and the ionized jet interpretation is further supported in 16 sources.
Paper Structure (8 sections, 1 figure, 1 table)

This paper contains 8 sections, 1 figure, 1 table.

Table of Contents

  1. Introduction
  2. Observations
  3. Sample Selection
  4. VLA K-band Observations
  5. H2O masers
  6. Discussion
  7. Comments on the compact morphologies observed
  8. Radio continuum proper motion

Figures (1)

  • Figure 1: Examples of the different morphologies observed: compact (top left, G35.39$-$00.33 mm2), double-peaked with lower level continuum connection (top right, IRAS 18553+0414), two or more individual compact features (bottom left, IRAS 18345$-$0641), and string-like (bottom right, IRAS 18566+0408). In every panel, the black and green contours represent the 1.3 cm continuum emission from our observations and those of Rosero16, respectively. The red $+$ symbols mark the position of the H$_2$O masers from this work, and the red circles in IRAS 18345$-$0641 and IRAS 18566+0408 show the position of the 6.7 GHz CH$_3$OH masers reported by Bartkiewicz09 and Araya10, respectively. The synthesized beam sizes are represented by the ellipses in the bottom left corner of each panel.