Stellar feedback and triggered star formation in the prototypical bubble RCW 120
Matteo Luisi, Loren D. Anderson, Nicola Schneider, Robert Simon, Slawa Kabanovic, Rolf Güsten, Annie Zavagno, Patrick S. Broos, Christof Buchbender, Cristian Gu… 展开作者
Matteo Luisi, Loren D. Anderson, Nicola Schneider, Robert Simon, Slawa Kabanovic, Rolf Güsten, Annie Zavagno, Patrick S. Broos, Christof Buchbender, Cristian Guevara, Karl Jacobs, Matthias Justen, Bernd Klein, Dylan Linville, Markus Röllig, Delphine Russeil, Jürgen Stutzki, Maitraiyee Tiwari, Leisa K. Townsley, Alexander G. G. M. Tielens
备注：
8 Pages, 4 Figures, 1 Table (+16 Page Supplementary Materials with 10 Figures). Published in Science Advances on April 9th, 2021, with free open access to the online article available at https://advances.sciencemag.org/content/7/15/eabe9511
Radiative and mechanical feedback of massive stars regulates star formation and galaxy evolution. Positive feedback triggers the creation of new stars by collecting dense shells of gas, while negative feedback disrupts star formation by shredding molecular clouds. Although key to understanding star formation, their relative importance is unknown. Here, we report velocity-resolved observations from the SOFIA (Stratospheric Observatory for Infrared Astronomy) legacy program FEEDBACK of the massive star-forming region RCW 120 in the [CII] 1.9-THz fine-structure line, revealing a gas shell expanding at 15 km/s. Complementary APEX (Atacama Pathfinder Experiment) CO J=3-2 345-GHz observations exhibit a ring structure of molecular gas, fragmented into clumps that are actively forming stars. Our observations demonstrate that triggered star formation can occur on much shorter time scales than hitherto thought (<0.15 million years), suggesting that positive feedback operates on short time periods.
We report on the near-infrared polarimetric observations of RCW 120 with the 1.4 m IRSF telescope. The starlight polarization of the background stars reveals for the first time the magnetic field of RCW 120. The global magnetic field of RCW 120 is along the direction of $20^\circ$, parallel to the Galactic plane. The field strength on the plane of the sky is $100\pm26\,μ$G. The magnetic field around the eastern shell shows evidence of compression by the HII region. The external pressure (turbulent pressure + magnetic pressure) and the gas density of the ambient cloud are minimum along the dire…
Understanding the mechanism of O star formation is one of the most important issues in current astrophysics. It is also an issue of keen interest how O stars affect their surroundings and trigger secondary star formation. An H\,\emissiontype{II} region RCW79 is one of the typical Spitzer bubbles alongside of RCW120. New observations of CO $J=$ 1--0 emission with Mopra and NANTEN2 revealed that molecular clouds are associated with RCW79 in four velocity components over a velocity range of 20 km s$^{-1}$. We hypothesize that two of the clouds collided with each other and the collision triggered …
We have made CO(J=2-1) observations towards the HII region RCW 49 and its ionizing source, the rich stellar cluster Westerlund 2 (hereafter Wd2), with the NANTEN2 sub-mm telescope. These observations have revealed that two molecular clouds in velocity ranges of -11 to +9 km/s and 11 to 21 km/s respectively, show remarkably good spatial correlations with the Spitzer IRAC mid-infrared image of RCW 49, as well a velocity structures indicative of localized expansion around the bright central regions and stellar cluster. This strongly argues that the two clouds are physically associated with RCW 49…
By means of different physical mechanisms, the expansion of HII regions can promote the formation of new stars of all masses. RCW 120 is a nearby Galactic HII region where triggered star formation occurs. This region is well-studied - there being a wealth of existing data - and is nearby. However, it is surrounded by dense regions for which far infrared data is essential to obtain an unbiased view of the star formation process and in particular to establish whether very young protostars are present. We attempt to identify all Young Stellar Objects (YSOs), especially those previously undetected…
We report a possibility that the high-mass star located in the HII region RCW 34 was formed by a triggering induced by a collision of molecular clouds. Molecular gas distributions of the $^{12}$CO and $^{13}$CO $J=$2-1, and $^{12}$CO $J=$3-2 lines toward RCW 34 were measured by using the NANTEN2 and ASTE telescopes. We found two clouds with the velocity ranges of 0-10 km s$^{-1}$ and 10-14 km s$^{-1}$. Whereas the former cloud as massive as ~2.7 x 10$^{4}$ Msun has a morphology similar to the ring-like structure observed in the infrared wavelengths, the latter cloud with the mass of ~10$^{3}$ …
A collision between two molecular clouds is one possible candidate for high-mass star formation. The HII region RCW 36, located in the Vela molecular ridge, contains a young star cluster with two O-type stars. We present new CO observations of RCW 36 with NANTEN2, Mopra, and ASTE using $^{12}$CO($J$ = 1-0, 2-1, 3-2) and $^{13}$CO($J$ = 2-1) line emissions. We have discovered two molecular clouds lying at the velocities $V_\mathrm{LSR} \sim$5.5 and 9 km s$^{-1}$. Both clouds are likely to be physically associated with the star cluster, as verified by the good spatial correspondence among the tw…
Massive clumps within the swept-up shells of bubbles, like that surrounding the galactic HII region RCW 120, have been interpreted in terms of the Collect and Collapse (C&C) mechanism for triggered star formation. The cold, dusty clumps surrounding RCW 120 are arranged in an almost spherical shell and harbour many young stellar objects. By performing high-resolution, three-dimensional SPH simulations of HII regions expanding into fractal molecular clouds, we investigate whether the formation of massive clumps in dense, swept-up shells necessarily requires the C&C mechanism. In a second step, w…
We present distributions of two molecular clouds having velocities of 2 km s$^{-1}$ and 14 km s$^{-1}$ toward RCW 38, the youngest super star cluster in the Milky Way, in the $^{12}$CO ($J=$1--0 and 3--2) and $^{13}$CO ($J=$1--0) transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the $J$=3--2 emission to the $J$=1--0 emission, the bridging feature connecting the two clouds in velocity and their morphological correspondence with the infrared dust emission. The total mass of the clouds and the cluster is too small to gravitati…
We present a study of the ionized, neutral atomic, and molecular gas associated with the ring nebula RCW 78 around the WR star HD 117688 (= WR 55). We based our study on CO observations carried out with the SEST and NANTEN telescopes. We report the detection of molecular gas with velocities in the range -56 to -33 km/s. The CO emission is mainly connected to the western section, with a total molecular mass of 1.3 x 10^5 solar masses. The analysis of the HI gas distribution reveals the HI envelope of the molecular cloud, while the radio continuum emission shows a ring-like structure, which is t…
Context. RCW 120 is a well-studied, nearby Galactic HII region with ongoing star formation in its surroundings. Previous work has shown that it displays a bubble morphology at mid-infrared wavelengths and has a massive layer of collected neutral material seen at sub-mm wavelengths. Given the well-defined photo-dissociation region (PDR) boundary and collected layer, it is an excellent laboratory to study the "collect and collapse" process of triggered star formation. Using Herschel Space Observatory data at 100, 160, 250, 350, and 500 micron, in combination with Spitzer and APEX-LABOCA data, we…
We present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected on the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an HII region is located, ionized by 3 OB stars. Intermediate mass stars (2 - 3 Msun) are detected of G- and K- spectral type. These stars are still in the pre-main sequence (PMS) phase. North of the HII region, a photon-dominated region is present, marking the edge of a de…
Star formation is a fundamental process for galactic evolution. One issue over the last several decades has been determining whether star formation is induced by external triggers or is self-regulated in a closed system. The role of an external trigger, which can effectively collect mass in a small volume, has attracted particular attention in connection with the formation of massive stellar clusters, which in the extreme may lead to starbursts. Recent observations have revealed massive cluster formation triggered by cloud-cloud collisions in nearby interacting galaxies, including the Magellan…
The discovery of several clusters of red supergiants towards l=24-30 deg has triggered interest in this area of the Galactic plane, where lines of sight are very complex and previous explorations of the stellar content were very preliminary. We attempt to characterise the stellar population associated with the HII region RCW173 (Sh2-60), located at l=25.3 deg, as previous studies have suggested that this population could be beyond the Sagittarius arm. We obtained UBV photometry of a stellar field to the south of the brightest part of RCW173, as well as spectroscopy of about twenty stars in the…
Triggered star formation around HII regions could be an important process. The Galactic HII region RCW 79 is a prototypical object for triggered high-mass star formation. We take advantage of Herschel data from the surveys HOBYS, "Evolution of Interstellar Dust", and Hi-Gal to extract compact sources in this region, complemented with archival 2MASS, Spitzer, and WISE data to determine the physical parameters of the sources (e.g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution. We obtained a sample of 50 compact sources, 96% of which are situated in…
We made CO ($J$ = 1--0, 2--1, and 3--2) observations toward an H{\sc ii} region RCW~32 in the Vela Molecular Ridge. The CO gas distribution associated with the H{\sc ii} region was revealed for the first time at a high resolution of 22 arcsec. The results revealed three distinct velocity components which show correspondence with the optical dark lanes and/or H$α$ distribution. Two of the components show complementary spatial distribution which suggests collisional interaction between them at a relative velocity of $\sim$4 km~s$^{-1}$. Based on these results, we present a hypothesis that cloud-…
Most stars born in clusters and recent results suggest that star formation (SF) preferentially occurs in subclusters. Studying the morphology and SF history of young clusters is crucial to understanding early SF. We identify the embedded clusters of young stellar objects (YSOs) down to M stars, in the HII regions RCW33, RCW32 and RCW27 of the Vela Molecular Ridge. Our aim is to characterise their properties, such as morphology and extent of the clusters in the three HII regions, derive stellar ages and the connection of the SF history with the environment. Through public photometric surveys su…
We analyzed the NANTEN2 13CO (J=2-1 and 1-0) datasets in NGC 2024. We found that the cloud consists of two velocity components, whereas the cloud shows mostly single-peaked CO profiles. The two components are physically connected to the HII region as evidenced by their close correlation with the dark lanes and the emission nebulosity. The two components show complementary distribution with a displacement of 0.4 pc. Such complementary distribution is typical to colliding clouds discovered in regions of high-mass star formation. We hypothesize that cloud-cloud collision between the two component…
A supersonic cloud-cloud collision produces a shock-compressed layer which leads to formation of high-mass stars via gravitational instability. We carried out a detailed analysis of the layer by using the numerical simulations of magneto-hydrodynamics which deal with colliding molecular flows at a relative velocity of 20 km s$^{-1}$ (Inoue & Fukui 2013). Maximum density in the layer increases from 1000 cm$^{-3}$ to more than $10^{5}$ cm$^{-3}$ within 0.3 Myrs by compression, and the turbulence and the magnetic field in the layer are amplified by a factor of $\sim 5$, increasing the mass accret…
We performed new comprehensive $^{13}$CO($J$=2--1) observations toward NGC 2024, the most active star forming region in Orion B, with an angular resolution of $\sim$100'' obtained with NANTEN2. We found that the associated cloud consists of two independent velocity components. The components are physically connected to the H{\sc ii} region as evidenced by their close correlation with the dark lanes and the emission nebulosity. The two components show complementary distribution with a displacement of $\sim$0.6 pc. Such complementary distribution is typical to colliding clouds discovered in regi…
We report on a study of the high-mass star formation in the the HII region W28A2 by investigating the molecular clouds extended over ~5-10 pc from the exciting stars using the 12CO and 13CO (J=1-0) and 12CO (J=2-1) data taken by the NANTEN2 and Mopra observations. These molecular clouds consist of three velocity components with the CO intensity peaks at V_LSR ~ -4 km s$^{-1}$, 9 km s$^{-1}$ and 16 km s$^{-1}$. The highest CO intensity is detected at V_LSR ~ 9 km s$^{-1}$, where the high-mass stars with the spectral types of O6.5-B0.5 are embedded. We found bridging features connecting these cl…
The ACS and NICMOS have been used to obtain new HST images of NGC 4038/4039 ("The Antennae"). These new observations allow us to better differentiate compact star clusters from individual stars, based on both size and color. We use this ability to extend the cluster luminosity function by approximately two magnitudes over our previous WFPC2 results, and find that it continues as a single power law, dN/dL propto L^alpha with alpha=-2.13+/-0.07, down to the observational limit of Mv~-7. Similarly, the mass function is a single power law dN/dM propto M^beta with beta=-2.10+/-0.20 for clusters wit…
M16, the Eagle Nebula, is an outstanding HII region where extensive high-mass star formation is taking place in the Sagittarius Arm, and hosts the remarkable "pillars" observed with HST. We made new CO observations of the region in the 12CO J=1--0 and J=2--1 transitions with NANTEN2. These observations revealed for the first time that a giant molecular cloud of $\sim 1.3 \times 10^5$ \Msun \ is associated with M16, which is elongated vertically to the Galactic plane over 35 pc at a distance of 1.8 kpc. We found a cavity of the molecular gas of $\sim 10$ pc diameter toward the heart of M16 at \…
Context: How do expanding HII regions interact with their environmental cloud? This is one of the central questions driving the SOFIA legacy program FEEDBACK. Here, we present a case study toward the prototypical H{\sc ii} region NGC7538. Methods: With SOFIA we mapped an area of ~210'^2 around NGC7538 in the [CII] line at 1.9THz. Complementary observed atomic carbon [CI] and high-J CO(8-7) data as well as archival NIR/FIR, cm continuum, CO(3-2) and HI data are folded into the analysis. Results: While the overall [CII] morphology follows the general ionized gas, the channel maps show multiple b…
Ionization feedback should impact the probability distribution function (PDF) of the column density around the ionized gas. We aim to quantify this effect and discuss its potential link to the Core and Initial Mass Function (CMF/IMF). We used in a systematic way Herschel column density maps of several regions observed within the HOBYS key program: M16, the Rosette and Vela C molecular cloud, and the RCW 120 H ii region. We fitted the column density PDFs of all clouds with two lognormal distributions, since they present a double-peak or enlarged shape in the PDF. Our interpretation is that the …
The Taurus-Auriga complex is the prototypical low-mass star forming region, and provides a unique testbed of the star formation process, which left observable imprints on the spatial, kinematic, and temporal structure of its stellar population. Taurus's rich observational history has uncovered peculiarities that suggest a complicated star forming event, such as members at large distances from the molecular clouds and evidence of an age spread. With Gaia, an in-depth study of the Taurus census is possible to confirm membership, identify substructure, and reconstruct its star formation history. …
