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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.

 

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 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.