Star formation in ‘the Brick’: ALMA reveals an active protocluster in the Galactic centre cloud G0.253+0.016

ABSTRACT G0.253+0.016, aka ‘the Brick’, is one of the most massive (>105 M⊙) and dense (>104 cm−3) molecular clouds in the Milky Way’s Central Molecular Zone. Previous observations have detected tentative signs of active star formation, most notably a water maser that is associated with a dust continuum source. We present ALMA Band 6 observations with an angular resolution of 0.13 arcsec (1000 AU) towards this ‘maser core’ and report unambiguous evidence of active star formation within G0.253+0.016. We detect a population of eighteen continuum sources (median mass ∼2 M⊙), nine of which are driving bi-polar molecular outflows as seen via SiO (5–4) emission. At the location of the water maser, we find evidence for a protostellar binary/multiple with multidirectional outflow emission. Despite the high density of G0.253+0.016, we find no evidence for high-mass protostars in our ALMA field. The observed sources are instead consistent with a cluster of low-to-intermediate-mass protostars. However, the measured outflow properties are consistent with those expected for intermediate-to-high-mass star formation. We conclude that the sources are young and rapidly accreting, and may potentially form intermediate- and high-mass stars in the future. The masses and projected spatial distribution of the cores are generally consistent with thermal fragmentation, suggesting that the large-scale turbulence and strong magnetic field in the cloud do not dominate on these scales, and that star formation on the scale of individual protostars is similar to that in Galactic disc environments.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab200 ◽

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.

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The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IV. Star Formation Signatures in G023.477

The Astrophysical Journal ◽

10.3847/1538-4357/ac2365 ◽

2021 ◽

Vol 923 (2) ◽

pp. 147

Author(s):

Kaho Morii ◽

Patricio Sanhueza ◽

Fumitaka Nakamura ◽

James M. Jackson ◽

Shanghuo Li ◽

...

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Line Emission ◽

High Mass ◽

Mass Star ◽

Dark Cloud ◽

Early Stages ◽

Star Formation Activity ◽

Prestellar Cores ◽

The Masses

Abstract With a mass of ∼1000 M ⊙ and a surface density of ∼0.5 g cm−2, G023.477+0.114, also known as IRDC 18310-4, is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 μm Dark High-mass Clumps in Early Stages. We have conducted ∼1.″2 resolution observations with ALMA at 1.3 mm in dust continuum and molecular line emission. We have identified 11 cores, whose masses range from 1.1 to 19.0 M ⊙. Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H2CO and CH3OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8–19 M ⊙). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.

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A golden age for maser surveys

Proceedings of the International Astronomical Union ◽

10.1017/s174392131701050x ◽

2017 ◽

Vol 13 (S336) ◽

pp. 219-224

Author(s):

Shari L. Breen

Keyword(s):

Star Formation ◽

Large Scale ◽

High Mass ◽

Mass Star ◽

Physical Conditions ◽

Multi Wavelength ◽

The Subject ◽

To Come ◽

Star Formation Regions ◽

Made In

AbstractMasers are becoming increasingly important probes of high-mass star formation, revealing details about the kinematics and physical conditions at the elusive, early stages of formation. Over the last decade significant investment has been made in a number of large-scale, sensitive maser surveys targeting transitions found in the vicinity of young, high-mass stars. Individually, these searches have led to valuable insights into maser populations, their associated star formation regions, and often revealed further details such as Galactic structure. In combination, they become even more powerful, especially when considered together with complementary multi-wavelength data. Another consequence of large maser surveys has been the identification of a number of especially interesting sources that have been the subject of subsequent detailed studies. I summarize the recent plethora of maser surveys, their results, and how they are contributing to our understanding of star formation. Ongoing searches will ensure a bright future of maser surveys in the decade to come.

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Molecular Gas Kinematics and High-Mass Star Formation in the Spiral Arms of the Milky Way

International Astronomical Union Colloquium ◽

10.1017/s0252921100008666 ◽

2004 ◽

Vol 191 ◽

pp. 143-144

Author(s):

A. Luna ◽

L. Carrasco ◽

L. Ortega ◽

L. Bronfman ◽

O. Yam

Keyword(s):

Star Formation ◽

Rigid Body ◽

Large Scale ◽

Milky Way ◽

Stellar System ◽

High Mass ◽

Rotational Line ◽

Molecular Gas ◽

Mass Star ◽

Spiral Arms

AbstractWe study the kinematic of the molecular gas using observations of the rotational line 12CO(J=1→0), and also the star formation traced by Ultra-Compact HII regions in the IV galactic quadrant (270° ≤ l ≤ 360°). Our results show that there is a connection between 1) high-mass star formation in the spiral arms of the Milky Way, 2) molecular gas of high column density, and 3) the large-scale rigid-body-like motion of the gas. The large-scale rigid-body-like motions observed in the arms imply that there is less angular momentum to dissipate in the formation processes of stellar systems. We show a multiple stellar system under study, embedded in its parent molecular cloud in the Carina arm region.

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Star Formation in Cooling Flows

Australian Journal of Physics ◽

10.1071/ph920501 ◽

1992 ◽

Vol 45 (4) ◽

pp. 501

Author(s):

PEJ Nulsen

Keyword(s):

Star Formation ◽

Mass Function ◽

Good Evidence ◽

Initial Mass Function ◽

High Mass ◽

Mass Star ◽

Cooling Flows ◽

Cooling Flow ◽

The Masses ◽

Intracluster Gas

There is good evidence that the intracluster gas near the centres of many clusters of galaxies is cooling over at least a decade in temperature. This results in an inflow, which is approximately steady where the cooling time of the gas is shorter than the age of the flow. X-ray observations indicate that the cooling gas must have substantial inhomogeneities. Non-linear development of thermal instability causes cooled gas clouds to be deposited throughout the region of the steady cooling flow. The masses of these clouds will be small, typically a lot less than a Jeans mass when they first form. It is argued that the difficulty of forming large clouds in the bulk of a cooling flow inhibits high mass star formation there. There is evidence of some 'normal' star formation near to the centres of many cooling flows where conditions are more favourable for the formation of giant clouds. The initial mass function is strongly affected by the star formation environment in cooling flows.

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A Circumstellar Disk in IRAS 23151+5912?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318000108 ◽

2017 ◽

Vol 13 (S336) ◽

pp. 315-316

Author(s):

Miguel A. Trinidad ◽

Tatiana Rodríguez-Esnard ◽

Josep M. Masqué

Keyword(s):

Radio Continuum ◽

High Mass ◽

Circumstellar Disk ◽

Mass Star ◽

Hii Region ◽

Star Forming ◽

Continuum Source ◽

Water Masers ◽

Water Maser ◽

The Continuum

AbstractWe present radio continuum and water maser observations toward the high-mass star-forming region IRAS 23151+5912 from the VLA and VLBA archive, respectively. We detected a continuum source, which seems to be a hypercompact HII region. In addition, a water maser group about 4″ south from the continuum source was detected. We present preliminary results of the analysis of three observations epochs of the water masers, which are tracing an arc-like structure. However, its kinematics is quite complex, since while one section of the structure seems to be moving away from one center, another section seems to be approaching.

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Different Evolutionary Stages in the Massive Star-forming Complex W3 Main

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000768 ◽

2012 ◽

Vol 8 (S292) ◽

pp. 116-116

Author(s):

Yuan Wang ◽

Henrik Beuther ◽

Qizhou Zhang ◽

Arjan Bik ◽

Javier A. Rodón ◽

...

Keyword(s):

Star Formation ◽

Large Scale ◽

Massive Star ◽

Chemical Properties ◽

Hii Regions ◽

High Mass ◽

Mass Star ◽

Star Forming ◽

Star Forming Regions ◽

And Chemical Properties

AbstractWe observed with the Submillimeter Array and IRAM 30 m telescope three high-mass star-forming regions in different evolutionary stages in the W3 high-mass star formation complex. These regions, i.e. W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are located within the same large-scale environment, which allows us to study rotation and outflows as well as chemical properties in an evolutionary sense. While we find multiple mm continuum sources toward all regions, these three subregions exhibit different dynamical and chemical properties, which indicates that they are in different evolutionary stages. Even within each sub-region, massive cores of different ages are found, e.g. in SMS2, sub-sources from the most evolved UCHii region to potential starless cores exist within 30 000 AU (left panel, Fig. 1). Outflows and rotational structures are found in SMS1 and SMS2. Evidence for interactions between the molecular cloud and the HII regions is found in the 13CO channel maps (right panel, Fig. 1), which may indicate triggered star formation.

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MAGMO: Mapping the Galactic Magnetic field through OH masers

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314011715 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 402-402 ◽

Cited By ~ 1

Author(s):

James A. Green ◽

Naomi M. McClure-Griffiths ◽

James L. Caswell ◽

Tim Robishaw ◽

Lisa Harvey-Smith ◽

...

Keyword(s):

Magnetic Field ◽

Star Formation ◽

Magnetic Fields ◽

Ground State ◽

Large Scale ◽

Zeeman Splitting ◽

High Mass ◽

Mass Star ◽

Galactic Magnetic Field ◽

Maser Emission

AbstractWe are undertaking a project (MAGMO) to examine large-scale magnetic fields pervading regions of high-mass star formation. The project will test if the orientations of weak large-scale magnetic fields can be maintained in the contraction (and field amplification) to the high densities encountered in high-mass star forming regions. This will be achieved through correlating targeted observations of ground-state hydroxyl (OH) maser emission towards hundreds of sites of high-mass star formation spread throughout the spiral arms of the Milky Way. Through the Zeeman splitting of the OH maser emission these observations will determine the strength and orientation of the in-situ magnetic field. The completion of the southern hemisphere Methanol Multibeam survey has provided an abundance of targets for ground-state OH maser observations, approximately 1000 sites of high-mass star formation. With this sample, much larger and more homogeneous than previously available, we will have the statistics necessary to outweigh random fluctuations and observe an underlying Galactic magnetic field if it exists. We presented details of the overall progress of the project illustrated by the results of a pilot sample of sources towards the Carina-Sagittarius spiral arm tangent, where a coherent field is implied.

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