scholarly journals Fragmentation and filaments at the onset of star and cluster formation

2019 ◽  
Vol 631 ◽  
pp. A72 ◽  
Author(s):  
Y. Lin ◽  
T. Csengeri ◽  
F. Wyrowski ◽  
J. S. Urquhart ◽  
F. Schuller ◽  
...  
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Structure Formation ◽  
Point Sources ◽  
High Mass ◽  
Small Scale ◽  
Physical Parameters ◽  
Star Formation Activity ◽  
Self Gravity ◽  
Compact Sources

Context. The structure formation of the dense interstellar material and the fragmentation of clumps into cores is a fundamental step for understanding how stars and stellar clusters form. Aims. We aim to establish a statistical view of clump fragmentation at subparsec scales based on a large sample of massive clumps selected from the ATLASGAL survey. Methods. We used the APEX/SABOCA camera at 350 μm to image clumps at a resolution of 8.″5, corresponding to physical scales of < 0.2 pc at a distance < 5 kpc. The majority of the sample consists of massive clumps that are weak or in absorption at 24 μm. We resolved spherical and filamentary structures and identified the population of compact sources. Complemented with archival Herschel data, we derived the physical properties, such as dust temperature, mass, and bolometric luminosity of clumps and cores. We used association with mid-infrared 22−24 μm and 70 μm point sources to determine the star formation activity of the cores. We then statistically assessed their physical properties and the fragmentation characteristics of massive clumps. Results. We detect emission at 350 μm toward all targets and find that it typically exhibits a filamentary (-like) morphology and hosts a population of compact sources. Using Gaussclumps, we identify 1120 compact sources and derive the physical parameters and star formation activity for 971 of these, 874 of which are associated with 444 clumps. We find a moderate correlation between the clump fragmentation levels with the clump gas density and the predicted number of fragments with a pure Jeans fragmentation scenario. We find a strong correlation between the mass of the most massive fragment and the total clump mass, suggesting that self-gravity may play an important role in the small-scale structure formation of the clumps. Finally, due to the improved angular resolution compared to ATLASGAL, we are able to identify 27 massive quiescent cores with Mcore >  100 M⊙ within 5 kpc; these are massive enough to be self-gravitating, but do not yet show any sign of star formation. This sample therefore comprises promising candidates of massive prestellar cores or deeply embedded high-mass protostars. Conclusions. The submillimeter observations of the massive clumps that are weak or completely dark at 24 μm reveal rich filamentary structures and an embedded population of compact cores. The maximum core mass is likely determined by the self-gravity of the clump. The rarity of massive prestellar core candidates implies short collapse timescales for dense structures.

scholarly journals Correlations between H α equivalent width and galaxy properties at z = 0.47: Physical or selection-driven?

2021 ◽  
Vol 503 (4) ◽  
pp. 5115-5133
Author(s):  
A A Khostovan ◽  
S Malhotra ◽  
J E Rhoads ◽  
S Harish ◽  
C Jiang ◽  
...  
Keyword(s):  
Star Formation ◽  
Equivalent Width ◽  
Luminosity Function ◽  
Mass Function ◽  
Stellar Mass ◽  
High Mass ◽  
Selection Effects ◽  
Star Formation Activity ◽  
Low Mass ◽  
Stellar Masses

ABSTRACT The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H α EW strongly anticorrelates with stellar mass as M−0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H α EW intrinsically correlates with stellar mass as W0∝M−0.16 ± 0.03 and decreases by a factor of ∼3 from 107 M⊙ to 1010 M⊙, while not correcting for selection effects steepens the correlation as M−0.25 ± 0.04. We find low-mass H α emitters to be ∼320 times more likely to have rest-frame EW&gt;200 Å compared to high-mass H α emitters. Combining the intrinsic W0–stellar mass correlation with an observed stellar mass function correctly reproduces the observed H α luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W0–stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H α emitters and not a byproduct of selection effects.

scholarly journals Dense cores in the Seahorse infrared dark cloud: physical properties from modified blackbody fits to the far-infrared–submillimetre spectral energy distributions

2020 ◽  
Vol 644 ◽  
pp. A82
Author(s):  
O. Miettinen
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Initial Conditions ◽  
High Mass ◽  
Spectral Energy ◽  
Mass Star ◽  
Wide Field ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Dense Cores

Context. Infrared dark clouds (IRDCs) can be the birth sites of high-mass stars, and hence determining the physical properties of dense cores in IRDCs is useful to constrain the initial conditions and theoretical models of high-mass star formation. Aims. We aim to determine the physical properties of dense cores in the filamentary Seahorse IRDC G304.74+01.32. Methods. We used data from the Wide-field Infrared Survey Explorer (WISE), Infrared Astronomical Satellite (IRAS), and Herschel in conjuction with our previous 350 and 870 μm observations with the Submillimetre APEX Bolometer Camera (SABOCA) and Large APEX BOlometer CAmera, and constructed the far-IR to submillimetre spectral energy distributions (SEDs) of the cores. The SEDs were fitted using single or two-temperature modified blackbody emission curves to derive the dust temperatures, masses, and luminosities of the cores. Results. For the 12 analysed cores, which include two IR dark cores (no WISE counterpart), nine IR bright cores, and one H II region, the mean dust temperature of the cold (warm) component, the mass, luminosity, H2 number density, and surface density were derived to be 13.3 ± 1.4 K (47.0 ± 5.0 K), 113 ± 29 M⊙, 192 ± 94 L⊙, (4.3 ± 1.2) × 105 cm−3, and 0.77 ± 0.19 g cm−3, respectively. The H II region IRAS 13039-6108a was found to be the most luminous source in our sample ((1.1 ± 0.4) × 103 L⊙). All the cores were found to be gravitationally bound (i.e. the virial parameter αvir < 2). Two out of the nine analysed IR bright cores (22%) were found to follow an accretion luminosity track under the assumptions that the mass accretion rate is 10−5 M⊙ yr−1, the stellar mass is 10% of the parent core mass, and the radius of the central star is 5 R⊙. Most of the remaing ten cores were found to lie within 1 dex below this accretion luminosity track. Seven out of 12 of the analysed cores (58%) were found to lie above the mass-radius thresholds of high-mass star formation proposed in the literature. The surface densities of Σ > 0.4 g cm−3 derived for these seven cores also exceed the corresponding threshold for high-mass star formation. Five of the analysed cores (42%) show evidence of fragmentation into two components in the SABOCA 350 μm image. Conclusions. In addition to the H II region source IRAS 13039-6108a, some of the other cores in Seahorse also appear to be capable of giving birth to high-mass stars. The 22 μm dark core SMM 9 is likely to be the youngest source in our sample that has the potential to form a high-mass star (96 ± 23 M⊙ within a radius of ~0.1 pc). The dense core population in the Seahorse IRDC has comparable average properties to the cores in the well-studied Snake IRDC G11.11-0.12 (e.g. Tdust and L agree within a factor of ~1.8); furthermore, the Seahorse, which lies ~60 pc above the Galactic plane, appears to be a smaller (e.g. three times shorter in projection, ~100 times less massive) version of the Snake. The Seahorse core fragmentation mechanisms appear to be heterogenous, including cases of both thermal and non-thermal Jeans instability. High-resolution follow-up studies are required to address the fragmented cores’ genuine potential of forming high-mass stars.

scholarly journals Central Molecular Zone of the Milky Way: Star Formation in an extreme Environment

2015 ◽  
Vol 11 (S315) ◽  
pp. 163-166
Author(s):  
Jens Kauffmann
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Spatial Scales ◽  
Extreme Environment ◽  
Average Density ◽  
High Mass ◽  
Density Structure ◽  
Star Formation Activity ◽  
Order Of Magnitude ◽  
Sgr A

AbstractThe Central Molecular Zone (CMZ; inner ~100 pc) hosts some of the most dense and massive molecular clouds of the Milky Way. These clouds might serve as local templates for dense clouds seen in nearby starburst galaxies or in the early universe. The clouds have a striking feature: they form stars at a very slow pace, considering their mass and high average density. Here we use interferometer data from ALMA and the SMA to show that this slow star formation is a consequence of the cloud density structure: CMZ clouds have a very flat density structure. They might, for example, exceed the average density of the Orion A molecular cloud by an order of magnitude on spatial scales ~5 pc, but CMZ “cores” of ~0.1 pc radius have masses and densities lower than what is found in the Orion KL region. This absence of highest–density gas probably explains the suppression of star formation. The clouds are relatively turbulent, and ALMA observations of H2CO and SiO indicate that the turbulence is induced by high–velocity shocks. We speculate that these shocks might prevent the formation of high–mass cores. It has been argued that the state of CMZ clouds depends on their position along the orbit around Sgr A*. Our incomplete data indicate no evolution in the density structure, and only a modest evolution in star formation activity per unit mass.

scholarly journals Semi-analytic forecasts for JWST – II. Physical properties and scaling relations for galaxies at z = 4–10

2019 ◽  
Vol 490 (2) ◽  
pp. 2855-2879 ◽  
Author(s):  
L Y Aaron Yung ◽  
Rachel S Somerville ◽  
Gergö Popping ◽  
Steven L Finkelstein ◽  
Harry C Ferguson ◽  
...  
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
High Redshift ◽  
Formation Rate ◽  
Distribution Functions ◽  
Scaling Relations ◽  
Physical Parameters ◽  
Model Parameters ◽  
Galaxy Populations ◽  
The Impact

ABSTRACT The long anticipated James Webb Space Telescope (JWST) will be able to directly detect large samples of galaxies at very high redshift. Using the well-established, computationally efficient Santa Cruz semi-analytic model, with recently implemented multiphase gas partitioning, and H2-based star formation recipes, we make predictions for a wide variety of galaxy properties for galaxy populations at z = 4–10. In this work, we provide forecasts for the physical properties of high-redshift galaxies and links to their photometric properties. With physical parameters calibrated only to z ∼ 0 observations, our model predictions are in good agreement with current observational constraints on stellar mass and star formation rate distribution functions up to z ∼ 8. We also provide predictions representing wide, deep, and lensed JWST survey configurations. We study the redshift evolution of key galaxy properties and the scaling relations among them. Taking advantage of our models’ high computational efficiency, we study the impact of systematically varying the model parameters. All distribution functions and scaling relations presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.

scholarly journals Theoretical considerations for star formation at low and high redshift

2015 ◽  
Vol 11 (S315) ◽  
pp. 247-253
Author(s):  
Bruce G. Elmegreen
Keyword(s):  
Star Formation ◽  
Mass Density ◽  
High Redshift ◽  
Distribution Functions ◽  
High Mass ◽  
Formation Processes ◽  
Accretion Rates ◽  
Major Merger ◽  
Cloud Cores ◽  
Self Gravity

AbstractStar formation processes in strongly self-gravitating cloud cores should be similar at all redshifts, forming single or multiple stars with a range of masses determined by local magneto-hydrodynamics and gravity. The formation processes for these cores, however, as well as their structures, temperatures, Mach numbers, etc., and the boundedness and mass distribution functions of the resulting stars, should depend on environment, as should the characteristic mass, density, and column density at which cloud self-gravity dominates other forces. Because the environments for high and low redshift star formation differ significantly, we expect the resulting gas to stellar conversion details to differ also. At high redshift, the universe is denser and more gas-rich, so the active parts of galaxies are denser and more gas rich too, leading to slightly shorter gas consumption timescales, higher cloud pressures, and denser, more massive, bound stellar clusters at the high mass end. With shorter consumption times corresponding to higher relative cosmic accretion rates, and with the resulting higher star formation rates and their higher feedback powers, the ISM has greater turbulent speeds relative to the rotation speeds, thicker gas disks, and larger cloud and star complex sizes at the characteristic Jeans length. The result is a more chaotic appearance at high redshift, bridging the morphology gap between today's quiescent spirals and today's major-mergers, with neither spiral nor major-merger processes actually in play at that time. The result is also a thick disk at early times, and after in-plane accretion from relatively large clump torques, a classical bulge. Today's disks are thinner, and torque-driven accretion is slower outside of inner barred regions. This paper reviews the basic processes involved with star formation in order to illustrate its evolution over time and environment.

scholarly journals Multi-scale analysis of the Monoceros OB 1 star-forming region

2019 ◽  
Vol 631 ◽  
pp. A3 ◽  
Author(s):  
Julien Montillaud ◽  
Mika Juvela ◽  
Charlotte Vastel ◽  
Jinhua He ◽  
Tie Liu ◽  
...  
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Scale Analysis ◽  
Junction Region ◽  
Star Forming ◽  
Multi Scale ◽  
Filament Dynamics ◽  
The North ◽  
Star Formation Activity ◽  
Multi Scale Analysis

Context. We started a multi-scale analysis of star formation in G202.3+2.5, an intertwined filamentary sub-region of the Monoceros OB1 molecular complex, in order to provide observational constraints on current theories and models that attempt to explain star formation globally. In the first paper (Paper I), we examined the distributions of dense cores and protostars and found enhanced star formation activity in the junction region of the filaments. Aims. In this second paper, we aim to unveil the connections between the core and filament evolutions, and between the filament dynamics and the global evolution of the cloud. Methods. We characterise the gas dynamics and energy balance in different parts of G202.3+2.5 using infrared observations from the Herschel and WISE telescopes and molecular tracers observed with the IRAM 30-m and TRAO 14-m telescopes. The velocity field of the cloud is examined and velocity-coherent structures are identified, characterised, and put in perspective with the cloud environment. Results. Two main velocity components are revealed, well separated in radial velocities in the north and merged around the location of intense N2H+ emission in the centre of G202.3+2.5 where Paper I found the peak of star formation activity. We show that the relative position of the two components along the sightline, and the velocity gradient of the N2H+ emission imply that the components have been undergoing collision for ~105 yr, although it remains unclear whether the gas moves mainly along or across the filament axes. The dense gas where N2H+ is detected is interpreted as the compressed region between the two filaments, which corresponds to a high mass inflow rate of ~1 × 10−3 M⊙ yr−1 and possibly leads to a significant increase in its star formation efficiency. We identify a protostellar source in the junction region that possibly powers two crossed intermittent outflows. We show that the H II region around the nearby cluster NCG 2264 is still expanding and its role in the collision is examined. However, we cannot rule out the idea that the collision arises mostly from the global collapse of the cloud. Conclusions. The (sub-)filament-scale observables examined in this paper reveal a collision between G202.3+2.5 sub-structures and its probable role in feeding the cores in the junction region. To shed more light on this link between core and filament evolutions, one must characterise the cloud morphology, its fragmentation, and magnetic field, all at high resolution. We consider the role of the environment in this paper, but a larger-scale study of this region is now necessary to investigate the scenario of a global cloud collapse.

scholarly journals Masers as evolutionary tracers of high-mass star formation

2012 ◽  
Vol 8 (S287) ◽  
pp. 156-160 ◽  
Author(s):  
Shari L. Breen ◽  
Simon P. Ellingsen
Keyword(s):  
Star Formation ◽  
Point Sources ◽  
Radio Continuum ◽  
High Mass ◽  
Mass Star ◽  
Evolutionary Scheme ◽  
Evolutionary Clock ◽  
The Common ◽  
Star Formation Regions ◽  
Made In

AbstractDetermining an evolutionary clock for high-mass star formation is an important step towards realising a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. We have carried out detailed studies of a large number of sources suspected of undergoing high-mass star formation and have found that common maser transitions offer the best opportunity to determine an evolutionary scheme for these objects. We have investigated the relative evolutionary phases of massive star formation associated with the presence or absence of combinations of water, methanol and main-line hydroxyl masers. The locations of the different maser species have been compared with the positions of 1.2 mm dust clumps, radio continuum, GLIMPSE point sources and Extended Green Objects. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species in high-mass star formation regions. We present our proposed sequence for the presence of the common maser species associated with young high-mass stars and highlight recent advances. We discuss future investigations that will be made in this area by comparing data from the Methanol Multibeam (MMB) Survey with chemical clocks from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey.

scholarly journals Probing the initial conditions of high-mass star formation

2019 ◽  
Vol 627 ◽  
pp. A85 ◽  
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.

scholarly journals Nobeyama 45 m mapping observations toward the nearby molecular clouds Orion A, Aquila Rift, and M17: Project overview

2019 ◽  
Vol 71 (Supplement_1) ◽  
Author(s):  
Fumitaka Nakamura ◽  
Shun Ishii ◽  
Kazuhito Dobashi ◽  
Tomomi Shimoikura ◽  
Yoshito Shimajiri ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
High Mass ◽  
Mass Star ◽  
Calibration Data ◽  
Star Forming ◽  
Star Formation Activity ◽  
Scientific Results

Abstract We carried out mapping observations toward three nearby molecular clouds, Orion A, Aquila Rift, and M 17, using a new 100 GHz receiver, FOREST, on the Nobeyama 45 m telescope. We describe the details of the data obtained such as intensity calibration, data sensitivity, angular resolution, and velocity resolution. Each target contains at least one high-mass star-forming region. The target molecular lines were 12CO (J = 1–0), 13CO (J = 1–0), C18O (J = 1–0), N2H+ (J = 1–0), and CCS (JN = 87–76), with which we covered the density range of 102 cm−3 to 106 cm−3 with an angular resolution of ∼20″ and a velocity resolution of ∼0.1 km s−1. Assuming the representative distances of 414 pc, 436 pc, and 2.1 kpc, the maps of Orion A, Aquila Rift, and M17 cover most of the densest parts with areas of about 7 pc × 15 pc, 7 pc × 7 pc, and 36 pc × 18 pc, respectively. On the basis of the 13CO column density distribution, the total molecular masses are derived to be $3.86 \times 10^{4}\, M_\odot$, $2.67 \times 10^{4}\, M_{\odot }$, and $8.1\times 10^{5}\, M_{\odot }$ for Orion A, Aquila Rift, and M17, respectively. For all the clouds, the H2 column density exceeds the theoretical threshold for high-mass star formation of ≳ 1 g cm−2 only toward the regions which contain current high-mass star-forming sites. For other areas, further mass accretion or dynamical compression would be necessary for future high-mass star formation. This is consistent with the current star formation activity. Using the 12CO data, we demonstrate that our data have enough capability to identify molecular outflows, and for the Aquila Rift we identify four new outflow candidates. The scientific results will be discussed in detail in separate papers.

scholarly journals Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357

2019 ◽  
Vol 625 ◽  
pp. A134 ◽  
Author(s):  
D. Russeil ◽  
M. Figueira ◽  
A. Zavagno ◽  
F. Motte ◽  
N. Schneider ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Massive Star ◽  
Spectral Energy Distribution ◽  
High Mass ◽  
Physical Parameters ◽  
Evolutionary Status ◽  
Mass Star ◽  
Massive Star Formation ◽  
Dense Cores

Aims. To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) that are able to form high-mass star(s). This is one of the purposes of the Herschel/HOBYS key programme. Here, we carry out the census and characterise of the properties of the MDCs population of the NGC 6357 H II region. Methods. Our study is based on the Herschel/PACS and SPIRE 70−500 μm images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract ~0.1 pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. Results. We obtain a complete census of 23 massive dense cores, amongst which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we have considered their evolutionary status, and suggest that only five of them are likely to form a high-mass star. Conclusions. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge or hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.

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