- ID:
- ivo://CDS.VizieR/J/ApJ/831/73
- Title:
- Galactic MCs associated with HII regions
- Short Name:
- J/ApJ/831/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relations between star formation and properties of molecular clouds (MCs) are studied based on a sample of star-forming regions in the Galactic Plane. Sources were selected by having radio recombination lines to provide identification of associated MCs and dense clumps. Radio continuum emission and mid-infrared emission were used to determine star formation rates (SFRs), while ^13^CO and submillimeter dust continuum emission were used to obtain the masses of molecular and dense gas, respectively. We test whether total molecular gas or dense gas provides the best predictor of SFR. We also test two specific theoretical models, one relying on the molecular mass divided by the free-fall time, the other using the free-fall time divided by the crossing time. Neither is supported by the data. The data are also compared to those from nearby star-forming regions and extragalactic data. The star formation "efficiency," defined as SFR divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all of the molecular gas.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/130/156
- Title:
- Galactic radio compact HII regions at 1.4GHz
- Short Name:
- J/AJ/130/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a new Very Large Array Galactic plane catalog at 1.4GHz (Cat. <J/AJ/130/586>) covering the first and second Galactic quadrants (340{deg}<=l<=120{deg}, |b|<=0.8{deg} with |b|<=1.8{deg} for 350{deg}<=l<=40{deg} and |b|<=2.5{deg} for 100{deg}<=l<=105{deg}) in conjunction with the MSX6C (Cat. <V/114>) Galactic plane mid-infrared catalog to supplement and better understand our 5GHz catalog (Cat. <J/ApJS/91/347>).
- ID:
- ivo://CDS.VizieR/J/PAZh/37/281
- Title:
- Galactic rotation curve from selected maser
- Short Name:
- J/PAZh/37/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes, proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to the Galactic center R_0_, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives.
134. Galactic Worms
- ID:
- ivo://CDS.VizieR/J/ApJ/390/108
- Title:
- Galactic Worms
- Short Name:
- J/ApJ/390/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog of candidates for the Galactic Worms that are possibly the walls surrounding the superbubbles is compiled; 118 isolated structures that appear both in HI and in IR (60 and 100{mu}m). 52 are possibly associated with HII regions. It is found that the 100-{mu}m emissivity increases systematically toward the Galactic interior, which is consistent with the increase of the general interstellar radiation field. The 100-{mu}m emissivity of the structures associated with the HII regions is larger than that of the structures without associated HII regions. The 60-100{mu}m ratio is large, 0.28+/-0.03, which may indicate that the grains associated with the atomic gas have a relatively large population of small grains. 35 structures appear in the 408MHz continuum. The IR and the radio continuum properties suggest that the 408MHz continuum emission in those structures is very likely thermal. The implications of these results on the ionization of gas far from the Galactic plane are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A122
- Title:
- G351.77-0.54 ALMA observations
- Short Name:
- J/A+A/621/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The hierarchical process of star formation has so far mostly been studied on scales from thousands of au to parsecs, but the smaller sub-1000 au scales of high-mass star formation are still largely unexplored in the submm regime. We aim to resolve the dust and gas emission at the highest spatial resolution to study the physical properties of the densest structures during high-mass star formation. We observed the high-mass hot core region G351.77-0.54 with the Atacama Large Millimeter Array with baselines extending out to more than 16 km. This allowed us to dissect the region at sub-50 au spatial scales. At a spatial resolution of 18/40au (depending on the distance), we identify twelve sub-structures within the inner few thousand au of the region. The brightness temperatures are high, reaching values greater 1000K, signposting high optical depth toward the peak positions. Core separations vary between sub-100 au to several 100 and 1000au. The core separations and approximate masses are largely consistent with thermal Jeans fragmentation of a dense gas core. Due to the high continuum optical depth, most spectral lines are seen in absorption. However, a few exceptional emission lines are found that most likely stem from transitions with excitation conditions above 1000K. Toward the main continuum source, these emission lines exhibit a velocity gradient across scales of 100-200au aligned with the molecular outflow and perpendicular to the previously inferred disk orientation.While we cannot exclude that these observational features stem from an inner hot accretion disk, the alignment with the outflow rather suggests that it stems from the inner jet and outflow region. The highest-velocity features are found toward the peak position, and no Hubble-like velocity structure can be identified. Therefore, these data are consistent with steady-state turbulent entrainment of the hot molecular gas via Kelvin-Helmholtz instabilities at the interface between the jet and the outflow. Resolving this high-mass star-forming region at sub-50au scales indicates that the hierarchical fragmentation process in the framework of thermal Jeans fragmentation can continue down to the smallest accessible spatial scales. Velocity gradients on these small scales have to be treated cautiously and do not necessarily stem from disks, but may be better explained with outflow emission. Studying these small scales is very powerful, but covering all spatial scales and deriving a global picture from large to small scales are the next steps to investigate.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A36
- Title:
- G346.056-0.021 and G346.077-0.056 radio images
- Short Name:
- J/A+A/612/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multiwavelength study of two southern Galactic H II regions G346.056-0.021 and G346.077-0.056 which are located at a distance of 10.9kpc. The distribution of ionized gas, cold and warm dust, and the stellar population associated with the two H II regions are studied in detail using measurements at near-infrared, mid-infrared, far-infrared, submillimeter and radio wavelengths. The radio continuum maps at 1280 and 610MHz were obtained using the Giant Metrewave Radio Telescope to probe the ionized gas. The dust temperature, column density, and dust emissivity maps were generated using modified blackbody fits in the far-infrared wavelength range 160-500um. Various near- and mid-infrared color and magnitude criteria were adopted to identify candidate ionizing star(s) and the population of young stellar objects in the associated field. The radio maps reveal the presence of diffuse ionized emission displaying distinct cometary morphologies. The 1280MHz flux densities translate to ZAMS spectral types in the range O7.5V-O7V and O8.5V-O8V for the ionizing stars of G346.056-0.021 and G346.077-0.056, respectively. A few promising candidate ionizing star(s) are identified using near-infrared photometric data. The column density map shows the presence of a large, dense dust clump enveloping G346.077-0.056. The dust temperature map shows peaks towards the two HII regions. The submillimeter image shows the presence of two additional clumps, one being associated with G346.056-0.021. The masses of the clumps are estimated to range between ~1400 and 15250M_{sun}_. Based on simple analytic calculations and the correlation seen between the ionized gas distribution and the local density structure, the observed cometary morphology in the radio maps is better explained invoking the champagne-flow model.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/398
- Title:
- Gas and stellar metallicities in HII galaxies
- Short Name:
- J/MNRAS/421/398
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the gas and stellar metallicities in a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. We eliminated all spectra with an insufficient signal-to-noise ratio, without strong emission lines and without the [OII] {lambda}3727{AA} line, which is necessary for the determination of the gas metallicity. This excludes galaxies with redshift ~<0.033. Our final sample contains ~700 spectra of HII galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/80
- Title:
- Gas phase oxygen abundances for HII regions
- Short Name:
- J/ApJ/887/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7138 HII regions across the disks of eight nearby galaxies using Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) optical integral field spectroscopy as part of the PHANGS-MUSE survey. After removing the first-order radial gradients present in each galaxy, we look at the statistics of the metallicity offset ({Delta}O/H) and explore azimuthal variations. Across each galaxy, we find low ({sigma}=0.03-0.05dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those HII regions that are 1{sigma} outliers toward both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher H{alpha} luminosity, lower H{alpha} velocity dispersion, younger star clusters, and associated molecular gas clouds showing higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased H{alpha} velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but cannot always cleanly associate this with the spiral pattern. Regions with enhanced and reduced abundances are found distributed throughout the disk, and in half of our galaxies we can identify subsections of spiral arms with clearly associated metallicity gradients. This suggests spiral arms play a role in organizing and mixing the interstellar medium.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A36
- Title:
- G53.541-0.011 ^12^CO and ^13^CO data cubes
- Short Name:
- J/A+A/569/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To investigate how a large-scale infrared bubble centered at l=53.9{deg} and b=0.2{deg} forms, and to study if star formation is taking place at the periphery of the bubble, we performed a multiwavelength study. Using the data from the Galactic Ring Survey (GRS) and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we performed a study of a large-scale infrared bubble with a size of about 16pc at a distance of 2.0kpc. We present the ^12^CO J=1-0, ^13^CO J=1-0, and C^18^O J=1-0 observations of HII region G53.54-0.01 (Sh2-82) obtained at the Purple Mountain Observation (PMO) 13.7m radio telescope to investigate the detailed distribution of associated molecular material. In addition, we also used radiorecombination line and VLA data. To select young stellar objects (YSOs) consistent with this region, we used the GLIMPSE I catalog.
- ID:
- ivo://CDS.VizieR/J/ApJ/488/224
- Title:
- 4.85 GHz fluxes of H II regions
- Short Name:
- J/ApJ/488/224
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an all-sky flux catalog of 760 H II regions with angular sizes ranging up to 10' at 4.85GHz. The data were compiled in a self-consistent manner from existing images of the Green Bank and Parkes-MIT-NRAO 4.85GHz radio continuum surveys. Nearly 35% of these H II regions have fluxes measured from these surveys for the first time. We compared our results to the previously published source catalogs which fit the same data. The new flux measurements agree within 5%-7% of these values and fall well within the formal errors. The diameters fall within 16% of the previously published fits to the same data, within the formal uncertainties of these values.
