- ID:
- ivo://CDS.VizieR/J/ApJ/901/51
- Title:
- Radio continuum param. of Galactic HII regions
- Short Name:
- J/ApJ/901/51
- Date:
- 15 Feb 2022 14:31:45
- Publisher:
- CDS
- Description:
- Sgr E is a massive star formation complex found toward the Galactic center that consists of numerous discrete, compact HII regions. It is located at the intersection between the central molecular zone (CMZ) and the far dust lane of the Galactic bar, similar to "hot spots" seen in external galaxies. Compared with other Galactic star formation complexes, the Sgr E complex is unusual because its HII regions all have similar radio luminosities and angular extents, and they are deficient in ~10{mu}m emission from their photodissociation regions (PDRs). Our Green Bank Telescope radio recombination line observations increase the known membership of Sgr E to 19 HII regions. There are 43 additional HII region candidates in the direction of Sgr E, 26 of which are detected for the first time here using MeerKAT 1.28GHz data. Therefore, the true HII region population of Sgr E may number >60. Using APEX SEDIGISM ^13^CO 2->1 data we discover a 3.0x10^5^M_{sun}_ molecular cloud associated with Sgr E, but find few molecular or far-infrared concentrations at the locations of the Sgr E HII regions. Comparison with simulations and an analysis of its radio continuum properties indicate that Sgr E formed upstream in the far dust lane of the Galactic bar a few million years ago and will overshoot the CMZ, crashing into the near dust lane. We propose that the unusual infrared properties of the Sgr E HII regions are caused by their orbits about the Galactic center, which have possibly stripped their PDRs.
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- ID:
- ivo://CDS.VizieR/J/ApJS/166/567
- Title:
- Radio Molecular lines in infrared dark clouds
- Short Name:
- J/ApJS/166/567
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified 41 infrared dark clouds from the 8um maps of the Midcourse Space Experiment (MSX), selected to be found within 1deg^2^ areas centered on known ultracompact HII regions. We have mapped these infrared dark clouds in N_2_H^+^ 1->0, CS 2->1, and C^18^O 1->0 emission using the Five College Radio Astronomy Observatory. The maps of the different species often show striking differences in morphologies, indicating differences in evolutionary state and/or the presence of undetected, deeply embedded protostars. We derive an average mass for these clouds using N_2_H^+^ column densities of >>2500M_{sun}_, a value comparable to that found in previous studies of high-mass star-forming cores using other mass tracers. The line widths of these clouds are typically 2.0-2.9km/s. Based on the fact that they are dark at 8um, compact, and massive, and have large velocity dispersions, we suggest that these clouds may be the precursor sites of intermediate- and high-mass star formation.
- ID:
- ivo://CDS.VizieR/J/ApJS/221/26
- Title:
- Radio observations of Galactic WISE HII regions
- Short Name:
- J/ApJS/221/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The WISE Catalog of Galactic H II Regions contains ~2000 H II region candidates lacking ionized gas spectroscopic observations. All candidates have the characteristic H II region mid-infrared morphology of WISE 12{mu}m emission surrounding 22{mu}m emission, and additionally have detected radio continuum emission. We here report Green Bank Telescope hydrogen radio recombination line (RRL) and radio continuum detections in the X-band (9GHz; 3cm) of 302 WISE H II region candidates (out of 324 targets observed) in the zone 225{deg}>=l>=-20{deg}, |b|<=6{deg}. Here we extend the sky coverage of our H II region Discovery Survey, which now contains nearly 800 HII regions distributed across the entire northern sky. We provide LSR velocities for the 302 detections and kinematic distances for 131 of these. Of the 302 new detections, 5 have (l, b, v) coordinates consistent with the Outer Scutum-Centaurus Arm (OSC), the most distant molecular spiral arm of the Milky Way. Due to the Galactic warp, these nebulae are found at Galactic latitudes >1{deg} in the first Galactic quadrant, and therefore were missed in previous surveys of the Galactic plane. One additional region has a longitude and velocity consistent with the OSC but lies at a negative Galactic latitude (G039.183-01.422; -54.9km/s). With Heliocentric distances >22kpc and Galactocentric distances >16kpc, the OSC H II regions are the most distant known in the Galaxy. We detect an additional three HII regions near ~=150{deg} whose LSR velocities place them at Galactocentric radii >19kpc. If their distances are correct, these nebulae may represent the limit to Galactic massive star formation.
- ID:
- ivo://CDS.VizieR/J/ApJS/165/338
- Title:
- Radio recombination lines in HII regions
- Short Name:
- J/ApJS/165/338
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report radio recombination line (RRL) and continuum observations of a sample of 106 Galactic HII regions made with the NRAO 140 Foot (43m) radio telescope in Green Bank, West Virginia. We believe this to be the most sensitive RRL survey ever made for a sample this large. Most of our source integration times range between 6 and 90 hr, yielding typical rms noise levels of ~1.0-3.5mK. Our data result from two different experiments performed, calibrated, and analyzed in similar ways. A CII survey was made at the 3.5cm wavelength to obtain accurate measurements of carbon radio recombination lines. When combined with atomic (CI) and molecular (CO) data, these measurements will constrain the composition, structure, kinematics, and physical properties of the photodissociation regions that lie on the edges of HII regions. A second survey was made at the 3.5cm wavelength to determine the abundance of ^3^He in the interstellar medium of the Milky Way. Together with measurements of the ^3^He^+^ hyperfine line, we get high-precision RRL parameters for H, ^4^He, and C. Here we discuss significant improvements in these data with both longer integrations and newly observed sources.
- ID:
- ivo://CDS.VizieR/J/A+A/171/261
- Title:
- Radio Recombination Lines of Southern HII Regions
- Short Name:
- J/A+A/171/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We tabulate velocities and other parameters of hydrogen recombination lines near 5GHz (H109{alpha} and H110{alpha}) for 316 HII regions observed with the Parkes 64-m radio telescope. Results of a new search for formaldehyde absorption are also listed. Source selection was based on the 5GHz continuum southern galactic plane survey of Haynes et al. (1978, 1979). Data is given for most H II regions in the galactic longitude range 210 to 360 degrees that show 5GHz continuum brightness temperature exceeding 1K (as observed with the 4 arcminute beam of the Parkes 64-m telescope), together with a selection of sources that are weaker or outside of this longitude range. Tabulated data include source coordinates, peak brightness, flux density, and angular size from the 5GHz continuum survey; radial velocities of detected formaldehyde absorption lines; recombination line peak brightness, radial velocity, and line width; derived electron temperature assuming LTE; derived kinematic distance from the Sun and galactocentric radius; and presence or absence of a visible optical counterpart. In cases where kinematic distance is ambiguous, both near and far distances are tabulated; a flag is given if there is a strong preference for near or far distance based on information such as H I or H2CO absorption measurements or visibility of an optical counterpart. Many of these radio HII regions lie beyond the range of optical detection, at distances exceeding several kpc; they thus provide a comprehensive coverage of the southern HII regions in the Galaxy over the longitude range 210 to 360 degrees and constitute a vital data base for the study of galactic structure.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A61
- Title:
- Radio spectra of globulettes in Carina nebula
- Short Name:
- J/A+A/602/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Carina nebula hosts a large number of globulettes. An optical study of these tiny molecular clouds shows that the majority are of planetary mass, but there are also those with masses of several tens up to a few hundred Jupiter masses. We seek to search for, and hopefully detect, molecular line emission from some of the more massive objects; in case of successful detection we aim to map their motion in the Carina nebula complex and derive certain physical properties. Methods.We carried out radio observations of molecular line emission in ^12^CO and ^13^CO (2-1) and (3-2) of 12 globulettes in addition to positions in adjacent shell structures using APEX. All selected objects were detected with radial velocities shifted relative to the emission from related shell structures and background molecular clouds. Globulettes along the western part of an extended dust shell show a small spread in velocity with small velocity shifts relative to the shell. This system of globulettes and shell structures in the foreground of the bright nebulosity surrounding the cluster Trumpler 14 is expanding with a few km/s relative to the cluster. A couple of isolated globulettes in the area move at similar speed. Compared to similar studies of the molecular line emission from globulettes in the Rosette nebula, we find that the integrated line intensity ratios and line widths are very different. The results show that the Carina objects have a different density/temperature structure than those in the Rosette nebula. In comparison the apparent size of the Carina globulettes is smaller, owing to the larger distance, and the corresponding beam filling factors are small. For this reason we were unable to carry out a more detailed modelling of the structure of the Carina objects in the way as performed for the Rosette objects. The Carina globulettes observed are compact and denser than objects of similar mass in the Rosette nebula. The distribution and velocities of these globulettes suggest that they have originated from eroding shells and elephant trunks. Some globulettes in the Trumpler 14 region are quite isolated and located far from any shell structures. These objects move at a similar speed as the globulettes along the shell, suggesting that they once formed from cloud fragments related to the same foreground shell.
- ID:
- ivo://CDS.VizieR/J/ApJ/850/195
- Title:
- RCW 57A NIR polarimetry and photometry
- Short Name:
- J/ApJ/850/195
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The influence of magnetic fields (B-fields) on the formation and evolution of bipolar bubbles, due to the expanding ionization fronts (I-fronts) driven by the HII regions that are formed and embedded in filamentary molecular clouds, has not been well-studied yet. In addition to the anisotropic expansion of I-fronts into a filament, B-fields are expected to introduce an additional anisotropic pressure, which might favor the expansion and propagation of I-fronts forming a bipolar bubble. We present results based on near-infrared polarimetric observations toward the central ~8'x8' area of the star-forming region RCW 57A, which hosts an HII region, a filament, and a bipolar bubble. Polarization measurements of 178 reddened background stars, out of the 919 detected sources in the JHKs bands, reveal B-fields that thread perpendicularly to the filament long axis. The B-fields exhibit an hourglass morphology that closely follows the structure of the bipolar bubble. The mean B-field strength, estimated using the Chandrasekhar-Fermi method (CF method), is 91+/-8{mu}G. B-field pressure dominates over turbulent and thermal pressures. Thermal pressure might act in the same orientation as the B-fields to accelerate the expansion of those I-fronts. The observed morphological correspondence among the B-fields, filament, and bipolar bubble demonstrate that the B-fields are important to the cloud contraction that formed the filament, to the gravitational collapse and star formation in it, and in feedback processes. The last one includes the formation and evolution of mid- infrared bubbles by means of B-field supported propagation and expansion of I-fronts. These may shed light on preexisting conditions favoring the formation of the massive stellar cluster in RCW 57A.
- ID:
- ivo://CDS.VizieR/J/A+A/616/L10
- Title:
- RCW120 fragmentation at 0.01pc scale
- Short Name:
- J/A+A/616/L10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Little is known about how high-mass stars form. Around 30% of the young high-mass stars in the Galaxy are observed at the edges of ionized (HII) regions. Therefore these are places of choice to study the earliest stages of high-mass star formation, especially towards the most massive condensations. High-spatial resolution observations in the millimeter range might reveal how these stars form and how they assemble their mass. We want to study the fragmentation process down to the 0.01pc scale in the most massive condensation (1700M_{sun}_) observed at the south-western edge of the HII region RCW 120 where the most massive Herschel cores (~124M_{sun}_ in average) could form high-mass stars. Using ALMA 3mm continuum observations towards the densest and most massive millimetric condensation (Condensation 1) of RCW 120, we used the getimages and getsources algorithms to extract the sources detected with ALMA and obtained their physical parameters. The fragmentation of the Herschel cores is discussed through their Jeans mass to understand the properties of the future stars. We extracted 18 fragments from the ALMA continuum observation at 3mm towards 8 cores detected with Herschel, whose mass and deconvolved size range from 2M_{sun}_ to 32M_{sun}_ and from 1.6mpc to 28.8mpc, respectively. The low degree of fragmentation observed, regarding to the thermal Jeans fragmentation, suggests that the observed fragmentation is inconsistent with ideal gravitational fragmentation and other ingredients such as turbulence or magnetic fields should be added in order to explain it. Finally, the range of fragments' mass indicates that the densest condensation of RCW 120 is a favourable place for the formation of high-mass stars with the presence of a probable UCHII region associated with the 27M_{sun}_ Fragment 1 of Core 2.
- ID:
- ivo://CDS.VizieR/J/MNRAS/367/1609
- Title:
- RCW 106 Giant Molecular Cloud 13CO mapping
- Short Name:
- J/MNRAS/367/1609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first paper in a series detailing the results of ^13^CO observations of a ~1{deg}^2^ region of the giant molecular cloud (GMC) complex associated with the HII region RCW 106. The ^13^CO observations are also the first stage of a multi-molecular line study of the same region. These observations were amongst the first made using the new on-the-fly mapping capability of the Australia Telescope National Facility Mopra Telescope. In the configuration used, the instrument provided a full width at half-maximum (FWHM) beam size of 33arcsec and a velocity resolution of 0.17km/s. The gas emission takes the form of a string of knots, oriented along an axis that extends from the north-west (NW) to the south-east (SE) of the field of the observations, and which is surrounded by a more extended, diffuse emission. We analyse the 2D integrated ^13^CO emission using the CLUMPFIND algorithm and identify 61 clumps. We compare the gas data in the GMC with the dust data provided by 21um Midcourse Space Experiment (MSX) and 1.2mm Swedish European Southern Observatory Submillimetre Telescope (SEST) images that we both regridded to the cell spacing of the Mopra data and smoothed to the same resolution.
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/256
- Title:
- RCW 106 Giant Molecular Cloud NH_3_ emission
- Short Name:
- J/MNRAS/441/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here we report observations of the two lowest inversion transitions of ammonia (NH_3_) with the 70-m Tidbinbilla radio telescope. The aim of the observations is to determine the kinetic temperatures in the dense clumps of the G333 giant molecular cloud associated with RCW 106 and to examine the effect that accurate measures of temperature have on the calculation of derived quantities such as mass. This project is part of a larger investigation to understand the time-scales and evolutionary sequence associated with high-mass star formation, particularly its earliest stages. Assuming that the initial chemical composition of a giant molecular cloud is uniform, any abundance variations within will be due to evolutionary state. We have identified 63 clumps using SEST Imaging Bolometer Array 1.2-mm dust continuum maps and have calculated gas temperatures for most (78 per cent) of these dense clumps. After using Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire 8.0{mu}m emission to separate the sample into infrared (IR)-bright and IR-faint clumps, we use statistical tests to examine whether our classification shows different populations in terms of mass and temperature.
