Deeply Embedded Protostellar Population in the Central Molecular Zone Suggested by H2O Masers and Dense Cores

AbstractThe Central Molecular Zone (CMZ), usually referring to the inner 500 pc of the Galaxy, contains a dozen of massive (~105M⊙) molecular clouds. Are these clouds going to actively form stars like Sgr B2? How are they affected by the extreme physical conditions in the CMZ, such as strong turbulence? Here we present a first step towards answering these questions. Using high-sensitivity, high angular resolution radio and (sub)millimeter observations, we studied deeply embedded star formation in six massive clouds in the CMZ, including the 20 and 50 km s−1 clouds, Sgr B1 off (as known as dust ridge clouds e/f), Sgr C, Sgr D, and G0.253 – 0.016. The VLA water maser observations suggest a population of deeply embedded protostellar candidates, many of which are new detections. The SMA 1.3 mm continuum observations reveal peaks in dust emission associated with the masers, suggesting the existence of dense cores. While our findings confirm that clouds such as G0.253 – 0.016 lack internal compact substructures and are quiescent in terms of star formation, two clouds (the 20 km s−1 cloud and Sgr C) stand out with clusters of water masers with associated dense cores which may suggest a population of deeply embedded protostars at early evolutionary phases. Follow-up observations with VLA and ALMA are necessary to confirm their protostellar nature.

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A sensitive survey for water masers towards Bok globules

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307012732 ◽

2007 ◽

Vol 3 (S242) ◽

pp. 146-147

Author(s):

I. de Gregorio-Monsalvo ◽

J. F. Gómez ◽

O. Suárez ◽

T. B. H. Kuiper ◽

G. Anglada ◽

...

Keyword(s):

Star Formation ◽

High Probability ◽

Angular Resolution ◽

Stellar Object ◽

High Angular Resolution ◽

Maser Emission ◽

Young Stellar Object ◽

Bok Globules ◽

Water Masers ◽

Water Maser

AbstractIn this work we report the most sensitive water maser survey towards Bok globules to date, using NASA's 70 m antenna in Robledo de Chavela (Spain). We observed 207 positions within the Clemens & Barvainis catalog that show indications of possible star formation or with a high probability of harboring a young stellar object. With this survey we have increased the number of Bok globules known to present water maser emission from three to nine. We have complemented these results with interferometric high-angular resolution observations towards some of our detections.

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The global star formation law: from dense cores to extreme starbursts

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001688 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 331-335

Author(s):

Yu Gao

Keyword(s):

Star Formation ◽

Linear Correlation ◽

Molecular Clouds ◽

High Redshift ◽

Gas Content ◽

Molecular Gas ◽

Giant Molecular Clouds ◽

Active Star ◽

Dense Cores ◽

The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

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Planck’s dusty GEMS

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833679 ◽

2018 ◽

Vol 620 ◽

pp. A60 ◽

Cited By ~ 6

Author(s):

R. Cañameras ◽

N. P. H. Nesvadba ◽

M. Limousin ◽

H. Dole ◽

R. Kneissl ◽

...

Keyword(s):

Star Formation ◽

Near Infrared ◽

Infrared Imaging ◽

High Redshift ◽

Dust Emission ◽

Galaxy Cluster ◽

Star Forming ◽

The Galaxy ◽

Mass Outflow ◽

Gas Accretion

We report the discovery of a molecular wind signature from a massive intensely star-forming clump of a few 109 M⊙, in the strongly gravitationally lensed submillimeter galaxy “the Emerald” (PLCK_G165.7+49.0) at z = 2.236. The Emerald is amongst the brightest high-redshift galaxies on the submillimeter sky, and was initially discovered with the Planck satellite. The system contains two magnificient structures with projected lengths of 28.5″ and 21″ formed by multiple, near-infrared arcs, falling behind a massive galaxy cluster at z = 0.35, as well as an adjacent filament that has so far escaped discovery in other wavebands. We used HST/WFC3 and CFHT optical and near-infrared imaging together with IRAM and SMA interferometry of the CO(4–3) line and 850 μm dust emission to characterize the foreground lensing mass distribution, construct a lens model with LENSTOOL, and calculate gravitational magnification factors between 20 and 50 in most of the source. The majority of the star formation takes place within two massive star-forming clumps which are marginally gravitationally bound and embedded in a 9 × 1010 M⊙, fragmented disk with 20% gas fraction. The stellar continuum morphology is much smoother and also well resolved perpendicular to the magnification axis. One of the clumps shows a pronounced blue wing in the CO(4–3) line profile, which we interpret as a wind signature. The mass outflow rates are high enough for us to suspect that the clump might become unbound within a few tens of Myr, unless the outflowing gas can be replenished by gas accretion from the surrounding disk. The velocity offset of –200 km s−1 is above the escape velocity of the clump, but not that of the galaxy overall, suggesting that much of this material might ultimately rain back onto the galaxy and contribute to fueling subsequent star formation.

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Dust properties and star formation of approximately a thousand local galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834553 ◽

2019 ◽

Vol 631 ◽

pp. A38 ◽

Cited By ~ 1

Author(s):

S. Lianou ◽

P. Barmby ◽

A. A. Mosenkov ◽

M. Lehnert ◽

O. Karczewski

Keyword(s):

Star Formation ◽

Spectral Energy Distribution ◽

Dust Emission ◽

Distribution Functions ◽

Spectral Energy ◽

Emission Properties ◽

Galaxy Type ◽

Dust Mass ◽

The Galaxy ◽

Stellar Masses

Aims. We derived the dust properties for 753 local galaxies and examine how these relate to some of their physical properties. We present the derived dust emission properties, including model spectral energy distribution (SEDs), star formation rates (SFRs) and stellar masses, as well as their relations. Methods. We modelled the global dust-SEDs for 753 galaxies, treated statistically as an ensemble within a hierarchical Bayesian dust-SED modelling approach, so as to derive their infrared (IR) emission properties. To create the observed dust-SEDs, we used a multi-wavelength set of observations, ranging from near-IR to far-IR-to-submillimeter wavelengths. The model-derived properties are the dust masses (Mdust), the average interstellar radiation field intensities (Uav), the mass fraction of very small dust grains (“QPAH” fraction), as well as their standard deviations. In addition, we used mid-IR observations to derive SFR and stellar masses, quantities independent of the dust-SED modelling. Results. We derive distribution functions of the properties for the galaxy ensemble and as a function of galaxy type. The mean value of Mdust for the early-type galaxies (ETGs) is lower than that for the late-type and irregular galaxies (LTGs and Irs, respectively), despite ETGs and LTGs having stellar masses spanning across the whole range observed. The Uav and “QPAH” fraction show no difference among different galaxy types. When fixing Uav to the Galactic value, the derived “QPAH” fraction varies across the Galactic value (0.071). The specific SFR increases with galaxy type, while this is not the case for the dust-specific SFR (SFR/Mdust), showing an almost constant star formation efficiency per galaxy type. The galaxy sample is characterised by a tight relationship between the dust mass and the stellar mass for the LTGs and Irs, while ETGs scatter around this relation and tend towards smaller dust masses. While the relation indicates that Mdust may fundamentally be linked to M⋆, metallicity and Uav are the second parameter driving the scatter, which we investigate in a forthcoming work. We used the extended Kennicutt–Schmidt (KS) law to estimate the gas mass and the gas-to-dust mass ratio (GDR). The gas mass derived from the extended KS law is on average ∼20% higher than that derived from the KS law, and a large standard deviation indicates the importance of the average star formation present to regulate star formation and gas supply. The average GDR for the LTGs and Irs is 370, and including the ETGs gives an average of 550.

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Probing Accretion Disks in AGN with Water Masers

International Astronomical Union Colloquium ◽

10.1017/s025292110004255x ◽

1997 ◽

Vol 163 ◽

pp. 113-125

Author(s):

Philip R. Maloney

Keyword(s):

Accretion Disk ◽

Accretion Disks ◽

Galactic Nuclei ◽

Quantitative Information ◽

X Rays ◽

Maser Emission ◽

Radiative Efficiency ◽

Physical Conditions ◽

Water Masers ◽

Water Maser

AbstractExtremely luminous extragalactic water masers – the so-called “megamasers”, with isotropic luminosities of tens to hundreds of solar luminosities – appear to be uniquely associated with active galactic nuclei. The recent survey of Braatz et al. indicates that 20% of Seyfert 2 galaxies have detectable water maser emission. Although originally suggested to arise in shocks, it now seems likely that the masers arise from the irradiation of high-pressure molecular gas by X-rays from the AGN. Quantitative modelling shows that the observed megamaser luminosities can plausibly be produced in this fashion. Both observational limits on the size scales and the high gas pressures required indicate that the water maser emission arises on very small scales, either in a circumnuclear “torus” or the accretion disk itself. In the best-studied case, NCG 4258, the masers are produced in a geometrically thin, warped accretion disk. The maser models can be used to derive quantitative information about the physical conditions in the disk, namely, the mass accretion rate, and therefore the radiative efficiency. I discuss the implications of water maser observations and models for the study of accretion disks and circumnuclear tori in AGN.

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A physically motivated core definition applied to dust emission observations of the Pipe nebula

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318008402 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 259-260

Author(s):

Birgit Hasenberger ◽

João Alves

Keyword(s):

Star Formation ◽

Formation Process ◽

Molecular Clouds ◽

Dust Emission ◽

Core Sample ◽

Critical Stage ◽

The Core ◽

Dense Cores ◽

A New Technique ◽

Cloud Medium

AbstractDense cores represent a critical stage in the star-formation process, but are not physically well-defined entities. We present a new technique to define core boundaries in observations of molecular clouds based on the physical properties of the cloud medium. Applying this technique to regions in the Pipe nebula, we find that our core boundaries differ from previous analyses, with potentially crucial implications for the statistical properties of the core sample.

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Magnetic Fields in Molecular Clouds

Symposium - International Astronomical Union ◽

10.1017/s007418090024148x ◽

2004 ◽

Vol 221 ◽

pp. 83-96

Author(s):

Tyler L. Bourke ◽

Alyssa A. Goodman

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Observational Data ◽

Observational Studies ◽

Molecular Clouds ◽

Large Scale ◽

Angular Resolution ◽

Protoplanetary Disks ◽

High Angular Resolution ◽

Dense Cores

Magnetic fields are believed to play an important role in the evolution of molecular clouds, from their large scale structure to dense cores, protostellar envelopes, and protoplanetary disks. How important is unclear, and whether magnetic fields are the dominant force driving star formation at any scale is also unclear. In this review we examine the observational data which address these questions, with particular emphasis on high angular resolution observations. Unfortunately the data do not clarify the situation. It is clear that the fields are important, but to what degree we don't yet know. Observations to date have been limited by the sensitivity of available telescopes and instrumentation. In the future ALMA and the SKA in particular should provide great advances in observational studies of magnetic fields, and we discuss which observations are most desirable when they become available.

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Global VLBA Observations of NGC 3079

Highlights of Astronomy ◽

10.1017/s153929960001933x ◽

1998 ◽

Vol 11 (2) ◽

pp. 972-973 ◽

Cited By ~ 2

Author(s):

Satoko Satoh ◽

M. Inoue ◽

N. Nakai ◽

K.M. Shibata ◽

S. Kameno ◽

...

Keyword(s):

Nuclear Region ◽

Systemic Velocity ◽

Unique Object ◽

The Galaxy ◽

Continuum Structure ◽

Water Masers ◽

Velocity Drift ◽

Absorption Features ◽

Water Maser

NGC 3079 has very luminous water megamaser from the nucleus, the peak of the spectrum being blueshifted by 180 km s-1 from the systemic velocity of the galaxy (Vsys = 1131 km s-1) (Henkel et al. 1984, Haschick & Baan 1985). Core-jet like continuum structure is also found in the nuclear region (Irwin & Seaquist 1988). No velocity drift for main features of water maser (VLSR — 941-975 km s1) has been shown (Nakai et al. 1995). However, the drift was recently detected for the maser of 1190 km s-1 (Nakai 1997). HI and OH absorptions were detected in the nucleus (Haschick & Baan 1985, Irwin & Seaquist 1991). Thus this galaxy is very unique object to investigate water masers, continuum structure and absorption features all together with VLBI.

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Probing the initial conditions of high-mass star formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834534 ◽

2019 ◽

Vol 627 ◽

pp. A85 ◽

Cited By ~ 4

Author(s):

Chuan-Peng Zhang ◽

Timea Csengeri ◽

Friedrich Wyrowski ◽

Guang-Xing Li ◽

Thushara Pillai ◽

...

Keyword(s):

Star Formation ◽

Multiple Scales ◽

Initial Conditions ◽

Dust Emission ◽

Radio Continuum ◽

High Mass ◽

Small Scale ◽

High Angular Resolution ◽

H Ii Regions ◽

Mass Star

Context. Fragmentation and feedback are two important processes during the early phases of star formation. Aims. Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby H ii regions. Methods. We present a high angular resolution study of a sample of massive proto-cluster clumps G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71. Combining infrared data at 4.5, 8.0, 24, and 70 μm, we use a few arcsecond resolution, radiometer and millimeter inteferometric data taken at 1.3 cm, 3.5 mm, 1.3 mm, and 870 μm to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring H ii regions. Taking advantage of that, we tested triggered star formation using a novel method where we study the alignment of the center of mass traced by dust emission at multiple scales. Results. The eight massive clumps, identified based on single-dish observations, have masses ranging from 228 to 2279 M⊙ within an effective radius of Reff ~ 0.5 pc. We detect compact structures towards six out of the eight clumps. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of Reff ~ 0.02 pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8 M⊙ at a small scale of Reff ~ 0.02 pc. We find that the two infrared quiet clumps with the lowest mass and lowest surface density with <300 M⊙ do not host any compact sources, calling into question their ability to form high-mass stars. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale (~1 pc). Conclusions. We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired.

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