The SCUBA polarized 850 microns thermal emission data of the region OMC-2 in Orion A are added to and homogeneously reduced with data already available in the region OMC-3. The data set shows that OMC-2 is a region generally less polarized than OMC-3. Where coincident, most of the 850 microns polarization pattern is similar to that measured in 350 microns polarization data. Only 850 microns polarimetry data have been obtained in and around MMS7, FIR1 & FIR2, and in the region south of FIR6. A realignment of the polarization vectors with the filament can be seen near FIR1 in the region south of OMC-3. An analysis shows that the energy injected by CO outflows and H2 jets associated to OMC-2 and OMC-3 does not appear to alter the polarization patterns at a scale of the 14'' resolution beam. A second order structure function analysis of the polarization position angles shows that OMC-2 is a more turbulent region than OMC-3. OMC-3 appears to be a clear case of a magnetically dominated region with respect to the turbulence. However for OMC-2 it is not clear that this is the case. A more in-depth analysis of five regions displayed along OMC-2/3 indicates a decrease of the mean polarization degree and an increase of the turbulent angular dispersion from north to south. A statistical analysis suggests the presence of two depolarization regimes in our maps. One regime including the effects of the cores, the other one excluding it.
We analyze the wavelength dependence of the far-infrared polarization fraction toward the OMC-1 star forming region using observations from HAWC+/SOFIA at 53, 89, 154, and 214 $μ$m. We find that the shape of the far-infrared polarization spectrum is variable across the cloud and that there is evidence of a correlation between the slope of the polarization spectrum and the average line-of-sight temperature. The slope of the polarization spectrum tends to be negative (falling toward longer wavelengths) in cooler regions and positive or flat in warmer regions. This is very similar to what was dis…
OMC-2/3 is one of the nearest embedded cluster-forming region that includes intermediate-mass protostars at early stages of evolution. A previous CO (3--2) mapping survey towards this region revealed outflow activity related to sources at different evolutionary phases. The present work aims to study the warm gas in the high-velocity emission from several outflows found in CO (3--2) emission by previous observations, determine their physical conditions, and make comparison with previous results in low-mass star-forming regions. We use the CHAMP+ heterodyne array on the APEX telescope to map the…
The Orion Nebula Cluster (ONC) is the nearest dense star-forming region at $\sim$400 pc away, making it an ideal target to study the impact of high stellar density and proximity to massive stars (the Trapezium) on protoplanetary disk evolution. The OMC1 molecular cloud is a region of high extinction situated behind the Trapezium in which actively forming stars are shielded from the Trapezium's strong radiation. In this work, we survey disks at high resolution with ALMA at three wavelengths with resolutions of 0.095\arcsec (3 mm; Band 3), 0.048\arcsec (1.3 mm; Band 6), and 0.030\arcsec (0.85 mm…
Dust emission and extinction in the Orion OMC-3 cloud
University of Helsinki（赫尔辛基大学）；Université de Toulouse, UPS-OMP, IRAP（图卢兹大学，UPS-OMP，IRAP）；Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale（巴黎萨克雷大学，法国国家科学研究中心，空间天体物理研究所）
The Herschel/HIFI spectral survey of OMC-2 FIR 4 (CHESS): An overview of the 480 to 1902 GHz range
对原恒星的宽带光谱巡天提供了丰富的关于恒星形成区的物理、化学和动力学结构和演化的视图。赫歇尔空间天文台开启了太赫兹领域的研究，让人们可以观测到许多电子的基本跃迁和许多其他物种的高能跃迁。对不同质量和演化状态的原恒星的化学清单和物理过程和性质进行比较分析是赫歇尔恒星形成区化学巡天（CHESS）关键计划的目标。这篇论文的重点是中等质量的原恒星，OMC-2 FIR 4。我们用Herschel机载HIFI光谱仪获得了OMC-2 FIR 4在480至1902 GHz范围内的光谱，并对谱线轮廓分量、激励和冷却进行了还原、谱线识别和广泛分析。我们检测到来自40个物种和同位素的719条谱线。线通量主要由CO、H2O和CH 3OH组成。线轮廓是复杂的，并随物种和上层能量而变化，但显然包含静态气体的签名，可能是由于外流的广泛组成部分，和前景云。我们发现了大量的证据，温暖，致密的气体，以及外流的视野。线通量代表在480至1250 GHz范围内使用HIFI检测到的7 L_Sol光度的2%。在总的线通量中，60%来自CO，13%来自H_2O，9%来自CH_3OH。与其他来源的类似HIFI光谱进行比较，将为恒星形成区域提供更多新的见解，一个恰当的例子是硫氧化物对猎户座KL和OMC-2 FIR 4的线冷却的相对贡献的两个数量级的差异。
Measurement of magnetic field strengths in a molecular cloud is essential for determining the criticality of magnetic support against gravitational collapse. In this paper, as part of the JCMT BISTRO survey, we suggest a new application of the Davis-Chandrasekhar-Fermi (DCF) method to estimate the distribution of magnetic field strengths in the OMC-1 region. We use observations of dust polarization emission at 450 $μ$m and 850 $μ$m, and C$^{18}$O (3-2) spectral line data obtained with the JCMT. We estimate the volume density, the velocity dispersion and the polarization angle dispersion in a b…
Young massive stars regulate the physical conditions, ionization, and fate of their natal molecular cloud. It is important to find tracers that help quantifying the stellar feedback processes that take place at different scales. We present ~85 arcmin^2 velocity-resolved maps of several submm molecular lines toward the closest high-mass star-forming region, OMC-1. The observed rotational lines include probes of warm and dense molecular gas that are difficult to detect from ground-based telescopes: CH+ (1-0), CO (10-9), HCO+ (6-5), and HCN (6-5). These lines trace an extended but thin layer of m…
We present the stability analysis of two regions, OMC-3 and OMC-4, in the massive and long molecular cloud complex of Orion A. We obtained $214~μ$m HAWC+/SOFIA polarization data, and we make use of archival data for the column density and C$^{18}$O (1-0) emission line. We find clear depolarization in both observed regions and that the polarization fraction is anti-correlated with the column density and the polarization-angle dispersion function. We find that the filamentary cloud and dense clumps in OMC-3 are magnetically supercritical and strongly subvirial. This region should be in the gravi…
Previous continuum observations from the MUSTANG camera on the Green Bank Telescope (GBT) of the nearby star-forming filament OMC 2/3 found elevated emission at 3.3 mm relative to shorter wavelength data. As a consequence, the inferred dust emissivity index obtained from modified black body dust spectra was considerably lower than what is typically measured on $\sim 0.1 \, {\rm pc}$ scales in nearby molecular clouds. Here we present new observations of OMC 2/3 collected with the MUSTANG-2 camera on the GBT which confirm this elevated emission. We also present for the first time sensitive 1 cm …
Filaments are an important part of star-forming interstellar clouds. Theie properties hold clues to their formation mechanisms and role in the star-formation process. We compare the properties of filaments in the Orion Molecular Cloud 3 (OMC-3), as seen in mid-infrared (MIR) absorption and far-infrared (FIR) dust emission. We calculated optical depth maps of the OMC-3 filaments based on the MIR absorption seen in Spitzer data and FIR dust emission observed with Herschel and the ArTéMiS instrument. The widths of the selected OMC-3 filament segments are in the range 0.03-0.1 pc, with similar ave…
We have studied the structure and kinematics of the dense molecular gas in the Orion Molecular Cloud 1 (OMC1) region with the N2H+ 3-2 line. The 6'x9' (~0.7x1.1 pc) region surrounding the Orion KL core has been mapped with the Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The combined SMA and SMT image having a resolution of ~5.4" (~2300 au) reveals multiple filaments with a typical width of 0.02-0.03 pc. On the basis of the non-LTE analysis using the N2H+ 3-2 and 1-0 data, the density and temperature of the filaments are estimated to be ~10^7 cm-3 and ~15-20 K, respectively…
Context. The star formation rates and stellar densities found in young massive clusters suggest that these stellar systems originate from gas at densities n(H$_2$) $>10^7$ cm$^{-3}$. Until today, however, the physical characterization of this ultra high density material remains largely unconstrained in observations. Aims. We investigated the density properties of the star-forming gas in the OMC-1 region located in the vicinity of the Orion Nebula Cluster (ONC). Methods. We mapped the molecular emission at 652 GHz in OMC-1 as part of the APEX-SEPIA660 Early Science. Results. We detect bright an…
We report the detection of a circular polarization signature in the Stokes $V$ profile of a 25 GHz Class I CH$_3$OH maser toward the high mass star forming region OMC-1. Such a feature usually constitutes a detection of the Zeeman effect. If due to a magnetic field in OMC-1, this would represent the first detection and discovery of the Zeeman effect in the 25 GHz Class I CH$_3$OH maser. The feature in Stokes $V$ is detected in two observations with different angular resolutions taken eight years apart with the Very Large Array (VLA); for our 2009 D-configuration observations, the fitted value …
We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA). We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 microns at angular resolutions of 5.1, 7.9, 14.0, and 18.7 arcseconds for the four bands, respectively. The photometric maps enable the computation of improved SEDs for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the `hourglass' configuration seen in previous…
Recent observations suggest a scenario in which filamentary structures in the ISM represent the first step towards clumps/cores and eventually star formation. The densest filaments would then fragment into prestellar cores owing to gravitational instability. We seek to understand the roles filamentary structures play in high-mass star formation. We mapped the integral-shaped filament (ISF) in NH3 (1, 1) and (2, 2). The whole filamentary structure is uniformly and fully sampled. We find that the morphology revealed by the map of velocity-integrated intensity of the NH3 (1, 1) line is closely as…
Star-forming molecular clouds are characterised by the ubiquity of intertwined filaments. The filaments have been observed in both high- and low-mass star-forming regions, and are thought to split into collections of sonic fibres. The locations where filaments converge are termed hubs, and these are associated with the young stellar clusters. However, the observations of filamentary structures within hubs at distances require a high angular resolution that limits the number of such studies conducted so far. The integral shaped filament of the Orion A molecular cloud is noted for harbouring sev…
Modeling the Far-Infrared Polarization Spectrum of a High-Mass Star Forming Cloud
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)（天体物理学跨学科探索与研究中心）；Northwestern University（西北大学）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Villanova University（维拉诺瓦大学）；SOFIA Science Center, NASA Ames Research Center（索菲亚科学中心，NASA艾姆斯研究中心）；University of Chicago（芝加哥大学）；Department of Astronomy, University of Virginia（弗吉尼亚大学天文学系）
The spectral energy distribution (SED) in the millimetre (mm) to centimetre (cm) range is a useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. While many studies have been carried out towards low- and high-mass protostars, little exists so far about solar-type protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born. We focus here on the OMC-2/3 solar-type protostars, which are bounded by nearby HII regions and which are, therefore, potentia…
Gravity-driven Emergence of Multi-fractal Density Structure in the Orion A Integral Shaped Filament
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（现代天文学和天体物理学教育部重点实验室（南京大学））；South-Western Institute for Astronomy Research, Yunnan University（云南大学西南天文研究所）
We report ALMA Cycle 3 observations in CO isotopes toward a dense core, MC27/L1521F in Taurus, which is considered to be at an early stage of multiple star formation in a turbulent environment. Although most of the high-density parts of this core are considered to be as cold as $\sim$10 K, high-angular resolution ($\sim$20 au) observations in $^{12}$CO ($J$ = 3--2) revealed complex warm ($>$15--60 K) filamentary/clumpy structures with the sizes from a few tens of au to $\sim$1,000 au. The interferometric observations of $^{13}$CO and C$^{18}$O show that the densest part with arc-like morpholog…
Winds from massive stars have velocities of 1000 km/s or more, and produce hot, high pressure gas when they shock. We develop a theory for the evolution of bubbles driven by the collective winds from star clusters early in their lifetimes, which involves interaction with the turbulent, dense interstellar medium of the surrounding natal molecular cloud. A key feature is the fractal nature of the hot bubble's surface. The large area of this interface with surrounding denser gas strongly enhances energy losses from the hot interior, enabled by turbulent mixing and subsequent cooling at temperatur…
Recently, there has been an increased interest in the study of the generation of low-energy cosmic rays (CRs; < 1 TeV) in shocks situated on the surface of a protostar or along protostellar jets. These locally accelerated CRs offer an attractive explanation for the high levels of non-thermal emission and ionisation rate, $ζ$, observed close to these sources. The high $ζ$ observed in some protostellar sources is generally attributed to shock-generated UV photons. The aim of this article is to show that when synchrotron emission and a high $ζ$ are measured in the same spatial region, a locally s…
The kinetic energy of supersonic turbulence within interstellar clouds is subject to cooling by dissipation in shocks and subsequent line radiation. The clouds are therefore susceptible to a condensation process controlled by the specific entropy. In a form analogous to the thermodynamic entropy, the entropy for supersonic turbulence is proportional to the log of the product of the mean turbulent velocity and the size scale. We derive a dispersion relation for the growth of entropic instabilities in a spherical self-gravitating cloud and find that there is a critical maximum dissipation time s…
The Prevalence of Turbulence-Regulated Multiphase Galactic Winds in Star-Forming Galaxies
Johns Hopkins University（约翰斯·霍普金斯大学）；Max-Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Universität Heidelberg（海德堡大学）；Northwestern University（西北大学）；Space Telescope Science Institute（太空望远镜科学研究所）；University of Pittsburgh（匹兹堡大学）
Using a suite of 3D hydrodynamical simulations of star-forming molecular clouds, we investigate how the density probability distribution function (PDF) changes when including gravity, turbulence, magnetic fields, and protostellar outflows and heating. We find that the density PDF is not lognormal when outflows and self-gravity are considered. Self-gravity produces a power-law tail at high densities and the inclusion of stellar feedback from protostellar outflows and heating produces significant time-varying deviations from a lognormal distribution at the low densities. The simulation with outf…
Magnetic fields have been included in cosmological simulations of galaxy formation only recently, due to advances in numerical techniques and a better understanding of the galaxy formation physics. In this paper, we develop a new subgrid model for the turbulent dynamo that takes place in the supersonic interstellar medium in star-forming galaxies. It is based on a mean-field approach that computes the turbulent kinetic energy at unresolved scales (the so-called subgrid scales) and modifies the induction equation to account for the corresponding $α$ dynamo. Our subgrid model depends on one free…
The extent to which turbulence mixes gas in the face of recurrent infusions of fresh metals by supernovae (SN) could help provide important constraints on the local star formation conditions. This includes predictions of the metallicity dispersion amongst metal poor stars, which suggests that the interstellar medium was not very well mixed at these early times. The purpose of this {\it Letter} is to help isolate, via a series of numerical experiments, some of the key processes that regulate turbulent mixing of SN elements in galactic disks. We study the gas interactions in small simulated patc…
The abundances of chemical elements and their depletion factors are essential parameters for understanding the composition of the gas and dust that are ultimately incorporated into stars and planets. Sulfur is an abundant but peculiar element in the sense that, despite being less volatile than other elements (e.g., carbon), it is not a major constituent of dust grains in diffuse interstellar clouds. Here, we determine the gas-phase carbon-to-sulfur abundance ratio, [C]/[S], and the sulfur abundance [S] in a dense star-forming cloud from new radio recombination lines (RRLs) detected with the Ye…
