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Abstract We present Very Large Array 1.3 cm continuum and 22.2 GHz H₂O maser observations of the high-mass protostellar object IRAS 19035+0641 A. Our observations unveil an elongated bipolar 1.3 cm continuum structure at scales ≲500 au, which, together with a rising in-band spectral index, strongly suggests that the radio emission toward IRAS 19035+0641 A arises from an ionized jet. In addition, eight individual water maser spots well aligned with the jet axis were identified. The StokesVspectrum of the brightest H₂O maser line (∼100 Jy) shows a possible Zeeman splitting and is well represented by the derivatives of two Gaussian components fitted to the StokesIprofile. The measuredB_losare 123 (±27) and 156 (±8) mG, translating to a preshock magnetic field of ≈7 mG. Subsequent observations to confirm the Zeeman splitting showed intense variability in all the water maser spots, with the brightest maser completely disappearing. The observed variability in a 1 yr timescale could be the result of an accretion event. These findings strengthen our interpretation of IRAS 19035+0641 A as a high-mass protostar in an early accretion/outflow evolutionary phase. 

Abstract G34.26 + 0.15 is a region of high-mass star formation that contains a broad range of young stellar objects in different stages of evolution, including a hot molecular core, hypercompact Hiiregions, and a prototypical cometary ultracompact Hiiregion. Previous high-sensitivity single-dish observations by our group resulted in the detection of broad 6035 MHz OH absorption in this region; the line showed a significant blueshifted asymmetry indicative of molecular gas expansion. We present high-sensitivity Karl G. Jansky Very Large Array (VLA) observations of the 6035 MHz OH line conducted to image the absorption and investigate its origin with respect to the different star formation sites in the region. In addition, we report detection of 6030 MHz OH absorption with the VLA and further observations of 4.7 GHz and 6.0 GHz OH lines obtained with the Arecibo Telescope. The 6030 MHz OH line shows a very similar absorption profile as the 6035 MHz OH line. We found that the 6035 MHz OH line absorption region is spatially unresolved at ∼2″ scales, and it is coincident with one of the bright ionized cores of the cometary Hiiregion that shows broad radio recombination line emission. We discuss a scenario where the OH absorption is tracing the remnants of a pole-on molecular outflow that is being ionized inside-out by the ultracompact Hiiregion. 

Abstract The study of the interaction between ionized jets, molecular outflows, and their environments is critical to understanding high-mass star formation, especially because jets and outflows are thought to be key in the transfer of angular momentum outward from accretion disks. We report a low spectral resolution Karl G. Jansky Very Large Array (VLA) survey for OH, NH₃, CH₃OH, and hydrogen radio recombination lines, toward a sample of 58 high-mass star-forming regions that contain numerous ionized jet candidates. The observations are from a survey designed to detect radio continuum; the novel aspect of this work is to search for spectral lines in broadband VLA data (we provide the script developed in this work to facilitate exploration of other data sets). We report detection of 25 GHz CH₃OH transitions toward 10 sources; 5 of them also show NH₃emission. We found that most of the sources detected in CH₃OH and NH₃have been classified as ionized jets or jet candidates and that the emission lines are coincident with, or very near (≲0.1 pc), these sources; hence, these molecular lines could be used as probes of the environment near the launching site of jets/outflows. No radio recombination lines were detected, but we found that the rms noise of stacked spectra decreases following the radiometer equation. Therefore, detecting radio recombination lines in a sample of brighter free–free continuum sources should be possible. This work demonstrates the potential of broadband VLA continuum observations as low resolution spectral-line scans. 

Abstract We report Very Large Array observations in theQband toward 10 ionized jet candidates to search for SiO emission, a well-known shocked gas tracer. We detected 7 mm continuum counterparts toward 90% of the jet candidates. In most cases, the jet candidate is located toward the center of the 7 mm core, and the high masses (≈100M_⊙) and densities (≈10⁷cm⁻³) of the cores suggest that the central objects are very young high-mass protostars. We detected SiOJ= 1–0 emission associated with six target sources. In all cases, the morphology and spectrum of the emission is consistent with what is expected for molecular jets along an outflow axis, thus confirming the jet nature of 60% of our sample. Our data suggest a positive correlation between the SiO luminosityL_SiO, and both the bolometric luminosityL_Boland the radio luminosityS_νd²of the driving sources. 

The dissipation of angular momentum of collapsing molecular cores is a key component in the formation of stars. Previous observations have reported that highly collimated protostellar jets can remove angular momentum from low-mass protostars. In contrast, there is no clear evidence that this occurs for high-mass protostars. Here we report the results of developing a data analysis platform to investigate whether molecular masers in the outflows of two high-mass star forming regions, DR21(OH) and W75N(B), trace net angular momentum. No statistically significant evidence was found for masers to trace net angular momentum transfer in these regions. However, our results show that high-angular resolution observations of masers near high-mass protostars have the potential of revealing this phenomenon at scales similar to the specific angular momentum carried by planets in our Solar System. 

Abstract We present Very Large Array C- , X- , and Q -band continuum observations, as well as 1.3 mm continuum and CO(2-1) observations with the Submillimeter Array toward the high-mass protostellar candidate ISOSS J23053+5953 SMM2. Compact centimeter continuum emission was detected near the center of the SMM2 core with a spectral index of 0.24(± 0.15) between 6 and 3.6 cm, and a radio luminosity of 1.3(±0.4) mJy kpc 2 . The 1.3 mm thermal dust emission indicates a mass of the SMM2 core of 45.8 (±13.4) M ⊙ , and a density of 7.1 (±1.2)× 10 6 cm −3 . The CO(2-1) observations reveal a large, massive molecular outflow centered on the SMM2 core. This fast outflow (>50 km s −1 from the cloud systemic velocity) is highly collimated, with a broader, lower-velocity component. The large values for outflow mass (45.2 ± 12.6 M ⊙ ) and momentum rate (6 ± 2 × 10 −3 M ⊙ km s −1 yr −1 ) derived from the CO emission are consistent with those of flows driven by high-mass YSOs. The dynamical timescale of the flow is between 1.5 and 7.2 × 10 4 yr. We also found from the C 18 O to thermal dust emission ratio that CO is depleted by a factor of about 20, possibly due to freeze-out of CO molecules on dust grains. Our data are consistent with previous findings that ISOSS J23053 + 5953 SMM2 is an emerging high-mass protostar in an early phase of evolution, with an ionized jet and a fast, highly collimated, and massive outflow. 

ABSTRACT Spectral lines from formaldehyde (H2CO) molecules at cm wavelengths are typically detected in absorption and trace a broad range of environments, from diffuse gas to giant molecular clouds. In contrast, thermal emission of formaldehyde lines at cm wavelengths is rare. In previous observations with the 100 m Robert C. Byrd Green Bank Telescope (GBT), we detected 2 cm formaldehyde emission towards NGC 7538 IRS1 – a high-mass protostellar object in a prominent star-forming region of our Galaxy. We present further GBT observations of the 2 and 1 cm H2CO lines to investigate the nature of the 2 cm H2CO emission. We conducted observations to constrain the angular size of the 2 cm emission region based on a East–West and North–South cross-scan map. Gaussian fits of the spatial distribution in the East–West direction show a deconvolved size (at half maximum) of the 2 cm emission of 50 arcsec ± 8 arcsec. The 1 cm H2CO observations revealed emission superimposed on a weak absorption feature. A non-LTE radiative transfer analysis shows that the H2CO emission is consistent with quasi-thermal radiation from dense gas ($${\sim}10^5$$–$$10^6$ cm−3). We also report detection of four transitions of CH3OH (12.2, 26.8, 28.3, 28.9 GHz), the (8,8) transition of NH3 (26.5 GHz), and a cross-scan map of the 13 GHz SO line that shows extended emission (>50 arcsec). 

We report on one of the highest sensitivity surveys for molecular lines in the frequency range 6.0 to 7.4 GHz conducted to date. The observations were done with the 305m Arecibo Telescope toward a sample of twelve intermediate/high-mass star forming regions. We searched for a large number of transitions of different molecules, including CH3OH and OH. The low RMS noise of our data (~5 mJy for most sources and transitions) allowed detection of spectral features that have not been seen in previous lower sensitivity observations of the sources, such as detection of excited OH and 6.7 GHz CH3OH absorption. A review of 6.7 GHz CH3OH detections indicates an association between absorption and radio continuum sources in high-mass star forming regions, although selection biases in targeted projects and low sensitivity of blind surveys imply incompleteness. Absorption of excited OH transitions was also detected toward three sources. In particular, we confirm a broad 6.035 GHz OH absorption feature in G34.26+0.15 characterized by an asymmetric blue-shifted wing indicative of expansion, perhaps a large scale outflow in this HII region. 

In this study we analyze 70 radio continuum sources associated with dust clumps and considered to be candidates for the earliest stages of high-mass star formation. The detection of these sources was reported by Rosero et al. (2016), who found most of them to show weak ( < 1 mJy) and compact ( < 0.6") radio emission. Herein, we used the observed parameters of these sources to investigate the origin of the radio continuum emission. We found that at least ∼ 30% of these radio detections are most likely ionized jets associated with high-mass protostars, but for the most compact sources we cannot discard the scenario that they represent pressure-confined HII regions. This result is highly relevant for recent theoretical models based on core accretion that predict the first stages of ionization from high-mass stars to be in the form of jets. Additionally, we found that properties such as the radio luminosity as a function of the bolometric luminosity of ionized jets from low and high-mass stars are extremely well-correlated. Our data improve upon previous studies by providing further evidence of a common origin for jets independently of luminosity.