On the duration of the embedded phase of star formation
Jaeyeon Kim, Mélanie Chevance, J. M. Diederik Kruijssen, Andreas Schruba, Karin Sandstrom, Ashley T. Barnes, Frank Bigiel, Guillermo A. Blanc, Yixian Cao, Danie… 展开作者
Jaeyeon Kim, Mélanie Chevance, J. M. Diederik Kruijssen, Andreas Schruba, Karin Sandstrom, Ashley T. Barnes, Frank Bigiel, Guillermo A. Blanc, Yixian Cao, Daniel A. Dale, Christopher M. Faesi, Simon C. O. Glover, Kathryn Grasha, Brent Groves, Cinthya Herrera, Ralf S. Klessen, Kathryn Kreckel, Janice C. Lee, Adam K. Leroy, Jérôme Pety, Miguel Querejeta, Eva Schinnerer, Jiayi Sun, Antonio Usero, Jacob L. Ward, Thomas G. Williams
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23 pages, 9 figures, 4 tables; accepted for publication in MNRAS (March 19, 2021)
Feedback from massive stars plays a key role in molecular cloud evolution. After the onset of star formation, the young stellar population is exposed by photoionization, winds, supernovae, and radiation pressure from massive stars. Recent observations of nearby galaxies have provided the evolutionary timeline between molecular clouds and exposed young stars, but the duration of the embedded phase of massive star formation is still ill-constrained. We measure how long massive stellar populations remain embedded within their natal cloud, by applying a statistical method to six nearby galaxies at 20-100 pc resolution, using CO, Spitzer 24$\rm\,μm$, and H$α$ emission as tracers of molecular clouds, embedded star formation, and exposed star formation, respectively. We find that the embedded phase (with CO and 24$\rm\,μm$ emission) lasts for $2{-}7$ Myr and constitutes $17{-}47\%$ of the cloud lifetime. During approximately the first half of this phase, the region is invisible in H$α$, making it heavily obscured. For the second half of this phase, the region also emits in H$α$ and is partially exposed. Once the cloud has been dispersed by feedback, 24$\rm\,μm$ emission no longer traces ongoing star formation, but remains detectable for another $2{-}9$ Myr through the emission from ambient CO-dark gas, tracing star formation that recently ended. The short duration of massive star formation suggests that pre-supernova feedback (photoionization and winds) is important in disrupting molecular clouds. The measured timescales do not show significant correlations with environmental properties (e.g. metallicity). Future JWST observations will enable these measurements routinely across the nearby galaxy population.
Stars are born in dense molecular filaments irrespective of their mass. Compression of the ISM by shocks cause filament formation in molecular clouds. Observations show that a massive star cluster formation occurs where the peak of gas column density in a cloud exceeds 10^23 cm^-2. In this study, we investigate the effect of the shock-compressed layer duration on filament/star formation and how the initial conditions of massive star formation are realized by performing three-dimensional (3D) isothermal magnetohydrodynamics (MHD) simulations with {gas inflow duration from the boundaries (i.e., …
Duration and properties of the embedded phase of star formation in 37 nearby galaxies from PHANGS-JWST
Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心）；Cosmic Origins Of Life (COOL) Research DAO（生命宇宙起源（COOL）研究DAO）；Kavli Institute for Particle Astrophysics & Cosmology, Stanford University（斯坦福大学卡弗里粒子天体物理与宇宙学研究所）；INAF — Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；European Southern Observatory（欧洲南方天文台）；Department of Physics, University of Arkansas（阿肯色大学物理系）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心拉格朗日实验室）；Department of Astronomy, The Ohio State University（俄亥俄州立大学天文学系）
The aim of this study is to locate previously unknown stellar clusters from the VISTA variables in the Vía Láctea Survey (VVV) catalogue data. The method, fitting a mixture model of Gaussian densities and background noise using the expectation maximization algorithm to a pre-filtered NIR survey stellar catalogue data, was developed by the authors for the UKIDSS Galactic Plane Survey (GPS). The search located 88 previously unknown mainly embedded stellar cluster candidates and 39 previously unknown sites of star formation in the 562 deg2 covered by VVV in the Galactic bulge and the southern dis…
We report the discovery of 652 star clusters, stellar groups and candidates in the Milky Way with WISE. Most of the objects are projected close to Galactic Plane and are embedded clusters. The present sample complements a similar study (Paper I) which provided 437 star clusters and alike. We find evidence that star formation processes span a wide range of sizes, from populous dense clusters to small compact embedded ones, sparse stellar groups or in relative isolation. The present list indicates multiple stellar generations during the embedded phase, with giant molecular clouds collapsing into…
We present a Herschel far-infrared study towards the rich massive star- forming complex G305, utilising PACS 70, 160 μm and SPIRE 250, 350, and 500 μm observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS, and Red MSX Source survey data available from previous studies. By applying a frequentist technique we are able to identify a sample of the most likely associations within our multi-wavelength dataset, that …
The earliest stages of star formation, when young stars are still deeply embedded in their natal clouds, represent a critical phase in the matter cycle between gas clouds and young stellar regions. Until now, the high-resolution infrared observations required for characterizing this heavily obscured phase (during which massive stars have formed, but optical emission is not detected) could only be obtained for a handful of the most nearby galaxies. One of the main hurdles has been the limited angular resolution of the Spitzer Space Telescope. With the revolutionary capabilities of the JWST, it …
Feedback from core collapse supernovae (SNe), the final stage of evolution of massive stars, is a key element in galaxy formation theory. The energy budget of SN feedback, as well as the duration over which SNe occur, are constrained by stellar lifetime models and the minimum mass star that ends its life as a SN. Simplifying approximations for this SN rate are ubiquitous in simulation studies. We show here how the choice of SN budget and timings ($t_0$ for the delay between star formation and the first SN, $τ_{\rm SN}$ for the duration of SN injection, and the minimum SN progenitor mass) drive…
Data mining techniques must be developed and applied to analyse the large public data bases containing hundreds to thousands of millions entries. The aim of this study is to develop methods for locating previously unknown stellar clusters from the UKIDSS Galactic Plane Survey catalogue data. The cluster candidates are computationally searched from pre-filtered catalogue data using a method that fits a mixture model of Gaussian densities and background noise using the Expectation Maximization algorithm. The catalogue data contains a significant number of false sources clustered around bright st…
The formation of a star is a dynamic process fed by the gravitational collapse of a molecular cloud core. Theoretical models and observations suggest that the majority of this infalling material settles into a protoplanetary disk before reaching the (proto)star and therefore that disk accretion processes are responsible for the rate at which the (proto)star grows. There is no fundamental reason why infall and disk accretion need to be instantaneously identical. Indeed, even within the disk it might be anticipated that there are regions of strong and weak accretion. Together these facts suggest…
The study of young massive clusters can provide key information for the formation of globular clusters, as they are often considered analogues. A currently unanswered question in this field is how long these massive clusters remain embedded in their natal gas, with important implications for the formation of multiple populations that have been used to explain phenomena observed in globular clusters. We present an analysis of ages and masses of the young massive cluster population of M83. Through visual inspection of the clusters, and comparison of their SEDs and position in colour-colour space…
We study the nature of feedback mechanisms in the 11 CLASH brightest cluster galaxies (BCGs) that exhibit extended ultraviolet and nebular line emission features. We estimate star formation rates (SFRs), dust masses, and starburst durations using a Bayesian photometry-fitting technique that accounts for both stellar and dust emission from the UV through far IR. By comparing these quantities to intracluster medium (ICM) cooling times and free-fall times derived from X-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the BCG SFR an…
The duration of a starburst is a fundamental parameter affecting the evolution of galaxies yet, to date, observational constraints on the durations of starbursts are not well established. Here we study the recent star formation histories (SFHs) of three nearby dwarf galaxies to rigorously quantify the duration of their starburst events using a uniform and consistent approach. We find that the bursts range from ~200 - ~400 Myr in duration resolving the tension between the shorter timescales often derived observationally with the longer timescales derived from dynamical arguments. If these three…
We present Ekster, a new method for simulating star clusters from birth in a live galaxy simulation that combines the smoothed-particle hydrodynamics (SPH) method Phantom with the $N$-body method PeTar. With Ekster, it becomes possible to simulate individual stars in a simulation with only moderately high resolution for the gas, allowing us to study whole sections of a galaxy rather than be restricted to individual clouds. We use this method to simulate star and star cluster formation in spiral arms, investigating massive GMCs and spiral arm regions with lower mass clouds, from two galaxy mode…
The embedded phase of star formation is the crucial phase where most of the stellar mass is assembled. Velocity-resolved spectra reveal an infalling envelope, bipolar outflows, and perhaps an infant circumstellar disk -- all locked together in a cosmic dance of gravitational collapse and magnetic winds. Densities and temperatures change by orders of magnitude as the protostar evolves, driving a chemistry as exotic as it is fascinating. I will review two examples of how to exploit chemistry and molecular spectroscopy to study the physics of low-mass star formation: energetic feedback and episod…
We present a detailed study of the complex ionization structure in a small (~250 pc) extended narrow line region (ENLR) cloud near Centaurus A using the Multi Unit Spectroscopic Explorer. This cloud is located in the so-called outer filament of ionized gas (about 15 kpc from the nucleus) where jet-induced star formation has been suggested to occur by different studies. We find that, despite the small size, a mixture of ionization mechanisms is operating, resulting in considerable complexity in the spatial ionization structure. The area includes two H II regions where star formation is occurrin…
The mass function of molecular clouds and clumps is shallower than the mass function of young star clusters, gas-embedded and gas-free alike, as their respective mass function indices are $β_0 \simeq 1.7$ and $β_\star \simeq 2$. We demonstrate that such a difference can arise from different mass-radius relations for the embedded-clusters and the molecular clouds (clumps) hosting them. In particular, the formation of star clusters with a constant mean {\it volume} density in the central regions of molecular clouds of constant mean {\it surface} density steepens the mass function from clouds to …
Spitzer Space Telescope observations of 15 spiral galaxies show numerous dense cores at 8 microns that are revealed primarily in unsharp mask images. The cores are generally invisible in optical bands because of extinction, and they are also indistinct at 8 microns alone because of contamination by more widespread diffuse emission. Several hundred core positions, magnitudes, and colors from the four IRAC bands are measured and tabulated for each galaxy. The larger galaxies, which tend to have longer and more regular spiral arms, often have their infrared cores aligned along these arms, with ad…
Star-forming regions that are visible at 3.6 microns and Halpha but not in the u,g,r,i,z bands of the Sloan Digital Sky survey (SDSS), are measured in five nearby spiral galaxies to find extinctions averaging ~3.8 mag and stellar masses averaging ~5x10^4 Msun. These regions are apparently young star complexes embedded in dark filamentary shock fronts connected with spiral arms. The associated cloud masses are ~10^7 Msun. The conditions required to make such complexes are explored, including gravitational instabilities in spiral shocked gas and compression of incident clouds. We find that insta…
We present arcsecond resolution 1.4mm observations of the high mass star forming region, Sharpless 2-157, that reveal the cool dust associated with the first stages of star formation. These data are compared with archival images at optical, infrared, and radio wavelengths, and complemented with new arcsecond resolution mid-infrared data. We identify a dusty young HII region, numerous infrared sources within the cluster envelope, and four starless condensations. Three of the cores lie in a line to the south of the cluster peak, but the most massive one is right at the center and associated with…
We present a multi-wavelength study to probe the star formation (SF) process in the molecular cloud linked with the G35.673-00.847 site (hereafter MCG35.6), which is traced in a velocity range of 53-62 km/s. Multi-wavelength images reveal a semi-ring-like feature (associated with ionized gas emission) and an embedded face-on ring-like feature (without the NVSS 1.4 GHz radio emission; where 1-sigma ~ 0.45 mJy/beam) in the MCG35.6. The semi-ring-like feature is originated by the ionizing feedback from a star with spectral type B0.5V-B0V. The central region of the ring-like feature does not conta…
The past decade has seen an increase of star formation studies made at the molecular cloud scale, motivated mostly by the deployment of a wealth of sensitive infrared telescopes and instruments. Embedded clusters, long recognised as the basic units of coherent star formation in molecular clouds, are now seen to inhabit preferentially cluster complexes tens of parsecs across. This chapter gives an overview of some important properties of the embedded clusters in these complexes and of the complexes themselves, along with the implications of viewing star formation as a molecular-cloud scale proc…
Stellar clusters are born in cold and dusty molecular clouds and the youngest clusters are embedded to various degrees in dusty dark molecular material. Such embedded clusters can be considered protocluster systems. The most deeply buried examples are so heavily obscured by dust that they are only visible at infrared wavelengths. These embedded protoclusters constitute the nearest laboratories for direct astronomical investigation of the physical processes of cluster formation and early evolution. I review the present state of empirical knowledge concerning embedded cluster systems and discuss…
To shed light on the time evolution of local star formation episodes in M33, we study the association between 566 Giant Molecular Clouds (GMCs), identified through the CO (J=2-1) IRAM-all-disk survey, and 630 Young Stellar Cluster Candidates (YSCCs), selected via Spitzer-24~$μ$m emission. The spatial correlation between YSCCs and GMCs is extremely strong, with a typical separation of 17~pc, less than half the CO(2--1) beamsize, illustrating the remarkable physical link between the two populations. GMCs and YSCCs follow the HI filaments, except in the outermost regions where the survey finds fe…
The ATLASGAL survey has characterised the properties of approximately 1000 embedded HII regions and found an empirical relationship between the clump mass and bolometric luminosity that covers 3-4 orders of magnitude. Comparing this relation with simulated clusters drawn from an initial mass function and using different star formation efficiencies we find that a single value is unable to fit the observed luminosity to mass ($L/M$) relation. We have used a Monte Carlo simulation to generate 200,000 clusters using the $L/M$-ratio as a constraint to investigate how the star formation efficiency c…
We investigate the dynamical evolution of star clusters during their formation, assuming that they are born from a turbulent starless clump of a given mass that is embedded within a parent self-gravitating molecular cloud characterized by a particular mass surface density. In contrast to the standard practice of most $N$-body studies, we do not assume that all stars are formed at once. Rather, we explore the effects of different star formation rates on the global structure and evolution of young embedded star clusters, also considering various primordial binary fractions and mass segregation l…
We present a novel infrared spectral energy distribution (SED) modeling methodology that uses likelihood-based weighting of the model fitting results to construct probabilistic H-R diagrams (pHRD) for X-ray identified, intermediate-mass (2-8 $M_{\odot}$), pre-main sequence young stellar populations. This methodology is designed specifically for application to young stellar populations suffering strong, differential extinction ($ΔA_V > 10$ mag), typical of Galactic massive star-forming regions. We pilot this technique in the Carina Nebula Complex (CNC) by modeling the 1-8 $μ$m SEDs of 2269 like…
NGC 2915 is a unique nearby galaxy that is classified as an isolated blue compact dwarf based on its optical appearance but has an extremely extended H i gas disk with prominent Sd-type spiral arms. To unveil the starburst-triggering mystery of NGC 2915, we performed a comprehensive analysis of deep VLT/MUSE integral field spectroscopic observations that cover the star-forming region in the central kiloparsec of the galaxy. We find that episodes of bursty star formation have recurred in different locations throughout the central region, and the most recent one peaked around 50 Myr ago. The bur…
We performed a multi-wavelength observation toward LkHa 101 embedded cluster and its adjacent 85arcmin*60arcmin region. The LkHa 101 embedded cluster is the first and only one significant cluster in California molecular cloud (CMC). These observations have revealed that the LkHa 101 embedded cluster is just located at the projected intersectional region of two filaments. One filament is the highest-density section of the CMC, the other is a new identified filament with a low-density gas emission. Toward the projected intersection, we find the bridging features connecting the two filaments in v…
We examine the combined effects of winds and photoionizing radiation from O--type stars on embedded stellar clusters formed in model turbulent molecular clouds covering a range of masses and radii. We find that feedback is able to increase the quantities of dense gas present, but decreases the rate and efficiency of the conversion of gas to stars relative to control simulations in which feedback is absent. Star formation in these calculations often proceeds at a rate substantially slower than the freefall rate in the dense gas. This decoupling is due to the weakening of, and expulsion of gas f…
We present a multi-wavelength data analysis of IRAS 05463+2652 (hereafter I05463+2652) to study star formation mechanisms. A shell-like structure around I05463+2652 is evident in the Herschel column density map, which is not associated with any ionized emission. Based on the Herschel sub-millimeter images, several parsec-scale filaments (including two elongated filaments, "s-fl" and "nw-fl" having lengths of ~6.4 pc and ~8.8 pc, respectively) are investigated in I05463+2652 site. Herschel temperature map depicts all these features in a temperature range of ~11-13 K. 39 clumps are identified an…
Connecting Star Formation in the Milky Way and Nearby Galaxies -II. An Observationally Driven Analytical Model for Predicting Cloud-Scale Star Formation Rates
Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Helmholtz-Institut für Strahlen- und Kernphysik (HISKP), Universität Bonn（波恩大学赫尔姆霍兹辐射与核物理研究所）；Charles University in Prague, Faculty of Mathematics and Physics, Astronomical Institute（布拉格查理大学数学物理学院天文研究所）
The physical evolution of low-mass protostars is relatively well-established, however, there are many open questions on the chemical structure of protostars. The chemical fingerprint generated in the early embedded phase of star formation may be transmitted to the later stages of star, planet and comet formation. The factors that influence the chemical fingerprint are then of interest to study, and determine whether the chemical structure is inherited from the parent cloud or product of the physical processes during star formation. Results of observations and modelling of molecules that trace …
Large interstellar organic molecules are potential precursors of prebiotic molecules. Their formation pathways and chemical relationships with one another and simpler molecules are therefore of great interest. In this paper, we address the relationship between two classes of large organic molecules, carbon chains and saturated complex organic molecules (COMs), at the early stages of star formation through observations of C4H and CH3OH. We surveyed these molecules with the IRAM 30m telescope toward 16 deeply embedded low-mass protostars selected from the Spitzer c2d ice survey. We find that CH3…
The filamentary nature of accretion streams found around embedded sources suggest that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals continuing to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores i…
We present initial results of the first large scale survey of embedded star clusters in molecular clouds in the Large Magellanic Cloud (LMC) using near-infrared (NIR) imaging from the VISTA Magellanic Clouds Survey (Cioni et al. 2011). We have explored a ~1.65 square degree area of the LMC, which contains the well-known star-forming region 30 Doradus as well as ~14 percent of the galaxy's CO clouds (Wong et al. 2011), and have identified 67 embedded cluster candidates, 45 of which are newly discovered as clusters. We have determined sizes, luminosities and masses for these embedded clusters, e…
Massive clumps, prior to the formation of any visible protostars, are the best candidates to search for the elusive massive starless cores. In this work we investigate the dust and gas properties of massive clumps selected to be 70 micron quiet, therefore good starless candidates. Our sample of 18 clumps has masses 300 < M < 3000 M_sun, radius 0.54 < R < 1.00 pc, surface densities Sigma > 0.05 g cm^-2 and luminosity/mass ratio L/M < 0.3. We show that half of these 70 micron quiet clumps embed faint 24 micron sources. Comparison with GLIMPSE counterparts shows that 5 clumps embed young stars of…
The known host galaxies of short-hard gamma-ray bursts (GRBs) to date are characterized by low to moderate star-formation rates and a broad range of stellar masses. In this paper, we positionally associate the recent unambiguously short-hard Swift GRB 100206A with a disk galaxy at redshift z=0.4068 that is rapidly forming stars at a rate of ~30 M_sun/yr, almost an order of magnitude higher than any previously identified short GRB host. Using photometry from Gemini, Keck, PAIRITEL, and WISE, we show that the galaxy is very red (g-K = 4.3 AB mag), heavily obscured (A_V ~ 2 mag), and has the high…
It has recently been suggested that high-density clusters have stellar age distributions narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency (SFE) per free-fall time, \eff, to their volume density profile. Our model predicts a steady decline of the star formation rate (SFR), which we quantify with its half-life…
The nearest massive star-forming complex, Cygnus-X, is widely used as a laboratory for star cluster formation and feedback processes, under the implicit assumption that all its components are located roughly at the same distance. We present a multi-wavelength study of a 15' x 15' field in southern Cygnus-X, where different components involving clustered star formation are overlapped. Preliminary results indicate that the Berkeley 87 and [DB2001] CL05 clusters are actually located at very different distances, invalidating previous claims of physical interaction between them. This shows the impo…
Globules and pillars, impressively revealed by the Spitzer and Herschel satellites, for example, are pervasive features found in regions of massive star formation. We studied the globule IRAS 20319+3958 in Cygnus X by means of visible and near-infrared imaging and spectroscopy, complemented with mid-infrared Spitzer/IRAC imaging, in order to obtain a census of its stellar content and the nature of its embedded sources. Our observations show that the globule contains an embedded aggregate of about 30 very young ($\lesssim 1$~Myr) stellar objects, for which we estimate a total mass of ~ 90 M_sun…
We investigate the formation of protostellar clusters during the collapse of dense molecular cloud cores with a focus on the evolution of potential and kinetic energy, the degree of substructure, and the early phase of mass segregation. Our study is based on a series of hydrodynamic simulations of dense cores, where we vary the initial density profile and the initial turbulent velocity. In the three-dimensional adaptive mesh refinement simulations, we follow the dynamical formation of filaments and protostars until a star formation efficiency of 20%. Despite the different initial configuration…
In this note we discuss the main results of a study of a massive binary with unequal mass ratio, q, embedded in an accretion disk, with its orbital rotation being opposed to that of the disk. When the mass ratio is sufficiently large, a gap opens in the disk, but the mechanism of gap formation is very different from the prograde case. Inward migration occurs on a timescale of t_ev ~ M_p/(dot M), where M_p is the mass of the less massive component (the perturber), and dot M is the accretion rate. When q<< 1, the accretion takes place mostly onto the more massive component, with the accretion ra…
The Timescales of Embedded Star Formation as Observed in STARFORGE
University of Washington（华盛顿大学）；Center for Computational Astrophysics, Flatiron Institute（平研究所计算天体物理中心）；Department of Astronomy, University of Texas at Austin（德克萨斯大学奥斯汀分校天文学系）；Space Telescope Science Institute（太空望远镜科学研究所）；Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University（西北大学交叉天体物理探索与研究中心及物理与天文系）；Department of Physics, University of Alberta（阿尔伯塔大学物理系）；National Radio Astronomy Observatory（国家射电天文台）；Max-Planc（马克斯·普朗克）
We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s$^{-1}$ cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H$_2$O maser observations. The submillimeter continuum emission shows five 1-pc scale clumps, each of which further fragments into several 0.1-pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H$_2$O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protosta…
We investigate the young stellar populations associated with DR 18 and ECX 6-21, which are two isolated globules irradiated by the O-type stars of the Cygnus OB2 association. Both are HII regions containing obvious tracers of recent and ongoing star formation. We also study smaller isolated molecular structures in their surroundings. Both globules contain their own embedded populations, with a higher fraction of the less-evolved classes. Masses and temperatures are estimated under the assumption of a common age of 1 Myr, which has been found to appropriately represent the general Cygnus OB2 YS…
We present a catalogue of starless and protostellar clumps associated with infrared dark clouds (IRDCs) in a 40 degrees wide region of the inner Galactic Plane (b<1). We have extracted the far-infrared (FIR) counterparts of 3493 IRDCs with known distance in the Galactic longitude range 15<l<55 and searched for the young clumps using Hi-GAL, the survey of the Galactic Plane carried out with the Herschel satellite. Each clump is identified as a compact source detected at 160, 250 and 350 mum. The clumps have been classified as protostellar or starless, based on their emission (or lack of emissio…
We analyze high-quality stellar catalogs for 24 young and nearby (within 1 kpc) embedded clusters and present a catalogue of 32 groups which have a high concentration of protostars. The median effective radius of these groups is 0.17 pc. The median protostellar and pre-main sequence star surface densities are 46 M_{\odot} pc^{-2} and 11 M_{\odot} pc^{-2}, respectively. We estimate the age of these groups using a model of constant birthrate and random accretion stopping and find a median value of 0.25 Myr. Some groups in Aquila and Serpens, Corona Australia and Ophichus L1688 show high protoste…
Measuring polarization from thermal dust emission can provide constraints on the magnetic field structure around embedded protostars. However, interpreting the observations is challenging without models that consistently account for both the complexity of the protostellar birth environment and polarization mechanisms. We aim to provide a better understanding with a focus on bridge-like structures such as that observed towards the protostellar multiple IRAS 16293--2422 by comparing synthetic polarization maps of thermal reemission with observations. We analyze the magnetic field properties asso…
Embedded clusters are ideal laboratories to understand the early phase of the dynamical evolution of clusters as well as the massive star formation. An interesting observational phenomenon is that some of the embedded clusters show mass segregation, i.e., the most massive stars are preferentially found near the cluster center. In this paper, we develop a new approach to describe mass segregation. Using this approach and the Two Micron All Sky Survey Point Source Catalog (2MASS PSC), we analyze eighteen embedded clusters in the Galaxy. We find that eleven of them are mass-segregated and that th…
We carried out a search for new infrared star clusters, stellar groups and candidates using WISE images, which are very sensitive to dust emission nebulae. We report the discovery of 437 embedded clusters and stellar groups that show a variety of structures, both in the stellar and nebular components. Pairs or small groupings of clusters are observed, suggesting multiple generations at the early formation stages. The resulting catalogue provides Galactic and equatorial coordinates, together with angular sizes for all objects. The nature of a representative test sub-sample of 14 clusters is inv…
Global simulations of accretion flows onto perturbers embedded in magnetized disks -I. MRI and jet formation in ideal MHD
Charles University（查理大学）；Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文研究所）；Niels Bohr International Academy, Niels Bohr Institute（尼尔斯·玻尔国际学院，尼尔斯·玻尔研究所）
