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

TL;DR

This study uses high-resolution VLA observations to analyze the morphologies and dynamics of ionized jets in compact radio sources, revealing diverse structures, proper motions, and variability that support shock ionization and jet classification.

Contribution

It provides detailed morphological, kinematic, and variability data on ionized jets in compact sources, enhancing understanding of their structures and ionization mechanisms.

Findings

Multiple jet morphologies observed, including string-like and compact sources.

Proper motions with an average velocity of 120 km/s detected in 10 sources.

Evidence supporting shock ionization as the main ionization mechanism.

Abstract

We present sub-arcsecond ($\theta\sim0.1^{\prime\prime}$) 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.