scholarly journals ATLASGAL – physical parameters of dust clumps associated with 6.7 GHz methanol masers

2019 ◽  
Author(s):  
S J Billington ◽  
J S Urquhart ◽  
C König ◽  
T J T Moore ◽  
D J Eden ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Evolutionary Process ◽  
Volume Density ◽  
High Mass ◽  
Physical Parameters ◽  
Mass Star ◽  
Large Area ◽  
The Galaxy ◽  
Area Survey ◽  
Methanol Masers

Abstract We have constructed the largest sample of dust-associated class II 6.7 GHz methanol masers yet obtained. New measurements from the the Methanol MultiBeam (MMB) Survey were combined with the 870 $\mu$m APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the 850 $\mu$m JCMT Plane Survey (JPS). Together with two previous studies we have now identified the host clumps for 958 methanol masers across the Galactic Plane, covering approximately 99 per cent of the MMB catalogue and increasing the known sample of dust-associated masers by over 30 per cent. We investigate correlations between the physical properties of the clumps and masers using distances and luminosities drawn from the literature. Clumps hosting methanol masers are significantly more compact and have higher volume densities than the general population of clumps. We determine a minimum volume density threshold of n(H2) ≥ 104 cm−3 for the efficient formation of intermediate- and high-mass stars. We find 6.7 GHz methanol masers are associated with a distinct part of the evolutionary process (Lbol/Mfwhm ratios of between 100.6 and 102.2) and have well defined turning on and termination points. We estimate the lower limit for the mass of embedded objects to be ≥6 M⊙ and the statistical lifetime of the methanol maser stage to be ∼3.3 × 104 yrs. This suggests that methanol masers are indeed reliable tracers of high mass star formation, and indicates that the evolutionary period traced by this marker is relatively rapid.

scholarly journals ATLASGAL, the APEX Telescope Large Area Survey of the Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 780-780
Author(s):  
F. Schuller ◽  
K. M. Menten ◽  
F. Wyrowski ◽  
H. Beuther ◽  
S. Bontemps ◽  
...  
Keyword(s):  
Galactic Plane ◽  
High Mass ◽  
Current Status ◽  
Continuum Emission ◽  
Mass Star ◽  
Large Area ◽  
Submillimeter Wavelengths ◽  
The Galaxy ◽  
First Results ◽  
Area Survey

AbstractSubmillimeter continuum emission traces high molecular column densities and, thus, dense cloud regions in which new stars are forming. Surveys of the Galactic plane in such emission have the potential of delivering an unbiased view of high-mass star formation throughout the Milky Way. Here we present the scope, current status and first results of ATLASGAL, an ongoing survey of the Galactic plane using the Large APEX Bolometer Camera (LABOCA) on the Atacama Pathfinder Experiment (APEX) telescope at the Chajnantor plateau in Chile. Aimed at mapping 360 square degrees at 870 μm, with a uniform sensitivity of 50 mJy/beam, this survey will provide the first unbiased sample of cold dusty clumps in the Galaxy at submillimeter wavelengths. These will be targets for molecular line follow-up observations and high resolution studies with ALMA and the EVLA.

scholarly journals ATLASGAL – relationship between dense star-forming clumps and interstellar masers

2020 ◽  
Vol 499 (2) ◽  
pp. 2744-2759
Author(s):  
S J Billington ◽  
J S Urquhart ◽  
C König ◽  
H Beuther ◽  
S L Breen ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Evolutionary Model ◽  
Volume Density ◽  
Physical Parameters ◽  
Large Area ◽  
Maser Emission ◽  
Star Forming ◽  
Area Survey ◽  
Methanol Masers ◽  
Water Masers

ABSTRACT We have used catalogues from several Galactic plane surveys and dedicated observations to investigate the relationship between various maser species and Galactic star-forming clumps, as identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. The maser transitions of interest are the 6.7 and 12.2-GHz methanol masers, 22.2-GHz water masers, and the masers emitting in the four ground-state hyperfine structure transitions of hydroxyl. We find clump association rates for the water, hydroxyl and methanol masers to be 56, 39, and 82 per cent, respectively, within the Galactic longitude range of 60○ > ℓ > −60○. We investigate the differences in physical parameters between maser associated clumps and the full ATLASGAL sample, and find that clumps coincident with maser emission are more compact with increased densities and luminosities. However, we find the physical conditions within the clumps are similar for the different maser species. A volume density threshold of n(H2) > 104.1 cm−3 for the 6.7-GHz methanol maser found in our previous study is shown to be consistent across for all maser species investigated. We find limits that are required for the production of maser emission to be 500 L⊙ and 6 M⊙, respectively. The evolutionary phase of maser associated clumps is investigated using the L/M ratio of clumps coincident with maser emission, and these have similar L/M ranges (∼100.2−102.7 L⊙/M⊙) regardless of the associated transitions. This implies that the conditions required for the production of maser emission only occur during a relatively narrow period during a star’s evolution. Lower limits of the statistical lifetimes for each maser species are derived, ranging from ∼0.4−2 × 104 yr and are in good agreement with the ‘straw man’ evolutionary model previously presented.

scholarly journals Modelled 3D distribution of OH/IR stars in the Galactic disc

2021 ◽  
Vol 502 (2) ◽  
pp. 3012-3020
Author(s):  
Y Uno ◽  
H Imai ◽  
K Shinano ◽  
H-H Qiao ◽  
J R Dawson ◽  
...  
Keyword(s):  
Simple Model ◽  
Galactic Plane ◽  
Phase 1 ◽  
Galactic Disc ◽  
Large Area ◽  
Luminosity Functions ◽  
Ir Stars ◽  
The Galaxy ◽  
Area Survey ◽  
Maser Sources

ABSTRACT We have modelled the 3D distribution of OH/IR stars in the Galactic plane, traced by 1612 MHz OH maser sources with classic double horned spectral profiles. We statistically analysed over 700 maser sources detected by the HI/OH/Recombination line survey of the Milky Way (THOR) and the Australia Telescope Compact Array interferometric follow-up observations of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). With a simple model constructed from a classical density distribution of stars and luminosity functions of OH maser sources in the Galaxy, we estimate the scale height, or the half thickness of the OH/IR star distribution along the Galactic disc to be 90–290 pc. The simple model also implies that there are ∼4000 OH/IR stars hosting 1612 MHz OH masers along the Galactic Plane. Therefore, next generation telescopes such as the Australian Square Kilometre Array Pathfinder (ASKAP) and SKA Phase 1 will detect about 80 per cent of such OH/IR stars in the Galaxy at a 10 mJy detection limit. Comparing the data of previously detected circumstellar 1612 MHz OH maser sources with those of THOR and SPLASH, the maser source lifetime is estimated to be ∼300 yr. This is likely a lower limit, since non-detections of masers in some cases could be affected by the flux variation of the maser source.

scholarly journals Methanol masers in the Herschel era Putting them in the star formation context

2012 ◽  
Vol 8 (S287) ◽  
pp. 492-496
Author(s):  
Michele Pestalozzi
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Plane ◽  
High Mass ◽  
Space Observatory ◽  
Methanol Maser ◽  
Open Time ◽  
The Galaxy ◽  
Methanol Masers ◽  
Using Data

AbstractMethanol masers are known to be among the most reliable tracers of high-mass stars in early stages of evolution. A number of searches across the Galaxy has yielded to date, a complete census of those masers in two thirds of the Milky Way, providing a catalogue of some 800 sources to be studied in depth. In particular, it is important to characterise the physical properties of the objects hosting methanol masers, and this is possible today using data from the Herschel Space Observatory (HSO). The exceptional spatial resolution of HSO and its wavelength coverage are perfectly tuned to put the methanol maser phase into its star formation context. This paper presents results on the characterisation of methanol maser hosts using Herschel data from the Hi-GAL project, an Open Time Key Project to survey the inner Galactic plane at 5 wavelengths between 70 and 500 μm.

scholarly journals The coordinated radio and infrared survey for high-mass star formation

2018 ◽  
Vol 615 ◽  
pp. A103 ◽  
Author(s):  
I. E. Kalcheva ◽  
M. G. Hoare ◽  
J. S. Urquhart ◽  
S. Kurtz ◽  
S. L. Lumsden ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Plane ◽  
High Mass ◽  
Spectral Energy ◽  
Mass Star ◽  
Large Area ◽  
Massive Star Formation ◽  
Extended Source ◽  
5 Ghz

A catalogue of 239 ultra-compact H II  regions (UCHIIs) found in the CORNISH survey at 5 GHz and 1.5″ resolution in the region 10° < l < 65°,  |b| < 1° is presented. This is the largest complete and well-selected sample of UCHIIs to date and provides the opportunity to explore the global and individual properties of this key state in massive star formation at multiple wavelengths. The nature of the candidates was validated, based on observational properties and calculated spectral indices, and the analysis is presented in this work. The physical sizes, luminosities and other physical properties were computed by utilising literature distances or calculating the distances whenever a value was not available. The near- and mid-infrared extended source fluxes were measured and the extinctions towards the UCHIIs were computed. The new results were combined with available data at longer wavelengths and the spectral energy distributions (SEDs) were reconstructed for 177 UCHIIs. The bolometric luminosities obtained from SED fitting are presented. By comparing the radio flux densities to previous observational epochs, we find about 5% of the sources appear to be time variable. This first high-resolution area survey of the Galactic plane shows that the total number of UCHIIs in the Galaxy is ~750 – a factor of 3–4 fewer than found in previous large area radio surveys. It will form the basis for future tests of models of massive star formation.

scholarly journals ALMA observations of RCW 120 Fragmentation at 0.01 pc scale

2018 ◽  
Vol 616 ◽  
pp. L10 ◽  
Author(s):  
M. Figueira ◽  
L. Bronfman ◽  
A. Zavagno ◽  
F. Louvet ◽  
N. Lo ◽  
...  
Keyword(s):  
Star Formation ◽  
High Spatial Resolution ◽  
Size Range ◽  
High Mass ◽  
Physical Parameters ◽  
Mass Star ◽  
Low Degree ◽  
The Galaxy ◽  
Continuum Observation ◽  
H Ii Region

Context. 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 (H II) regions. Therefore these are places of choice to study the earliest stages of high-mass star formation, especially toward the most massive condensations. High spatial resolution observations in the millimeter range might reveal how these stars form and how they assemble their mass. Aims. We want to study the fragmentation process down to the 0.01 pc scale in the most massive condensation (1700 M⊙) observed at the southwestern edge of the H ii region RCW 120 where the most massive Herschel cores (~124 M⊙ in average) could form high-mass stars. Methods. Using ALMA 3 mm continuum observations toward 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 these future stars. Results. We extracted 18 fragments from the ALMA continuum observation at 3 mm toward eight cores detected with Herschel, whose mass and deconvolved size range from 2 M⊙ to 32 M⊙ and from 1.6 mpc to 28.8 mpc, respectively. The low degree of fragmen- tation observed regarding 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 to explain this inconsistency. Finally, the range of the mass of the fragments indicates that the densest condensation of RCW 120 is a favorable place for the formation of high-mass stars with the presence of a probable UCH ii region associated with the 27 M⊙ Fragment 1 of Core 2.

scholarly journals GASTON: Galactic Star Formation with NIKA2. Evidence for the mass growth of star-forming clumps

2021 ◽  
Author(s):  
A J Rigby ◽  
N Peretto ◽  
R Adam ◽  
P Ade ◽  
M Anderson ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Galactic Plane ◽  
High Sensitivity ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Mass Growth ◽  
Star Forming ◽  
Compact Source

Abstract Determining the mechanism by which high-mass stars are formed is essential for our understanding of the energy budget and chemical evolution of galaxies. By using the New IRAM KIDs Array 2 (NIKA2) camera on the Institut de Radio Astronomie Millimétrique (IRAM) 30-m telescope, we have conducted high-sensitivity and large-scale mapping of a fraction of the Galactic plane in order to search for signatures of the transition between the high- and low-mass star-forming modes. Here, we present the first results from the Galactic Star Formation with NIKA2 (GASTON) project, a Large Programme at the IRAM 30-m telescope which is mapping ≈2 deg2 of the inner Galactic plane (GP), centred on ℓ = 23${_{.}^{\circ}}$9, b = 0${_{.}^{\circ}}$05, as well as targets in Taurus and Ophiuchus in 1.15 and 2.00 mm continuum wavebands. In this paper we present the first of the GASTON GP data taken, and present initial science results. We conduct an extraction of structures from the 1.15 mm maps using a dendrogram analysis and, by comparison to the compact source catalogues from Herschel survey data, we identify a population of 321 previously-undetected clumps. Approximately 80 per cent of these new clumps are 70 μm-quiet, and may be considered as starless candidates. We find that this new population of clumps are less massive and cooler, on average, than clumps that have already been identified. Further, by classifying the full sample of clumps based upon their infrared-bright fraction – an indicator of evolutionary stage – we find evidence for clump mass growth, supporting models of clump-fed high-mass star formation.

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

scholarly journals The Dark Blue Compact Dwarf Galaxy NGC 2915

1997 ◽  
Vol 14 (1) ◽  
pp. 77-80 ◽  
Author(s):  
Gerhardt R. Meurer
Keyword(s):  
Dark Matter ◽  
Mass Distribution ◽  
Dwarf Galaxy ◽  
Dark Matter Halo ◽  
High Mass ◽  
Mass Star ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Dark Blue ◽  
Blue Compact Dwarf Galaxy

AbstractRecent results on NGC 2915, the first blue compact dwarf galaxy to have its mass distribution modelled, are summarised. NGC 2915 is shown to have HI well beyond its detected optical extent. Its rotation curve is well determined and fit with maximum disk mass models. The dark matter halo dominates the mass distribution at nearly all radii, and has a very dense core compared to those of normal galaxies. High-mass star formation energises the HI in the centre of the galaxy, but appears to be maintained in viriai equilibrium with the dark matter halo. The implications of these results are briefly discussed.

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