ALMA Fragmented Source Catalog in Orion (FraSCO). I. Outflow interaction within an embedded cluster in OMC-2/FIR 3, FIR 4, and FIR 5

Funding: This work was supported by NAOJ ALMA Scientific Research grant No. 2022-22B. The present study was supported by JSPS KAKENHI grants (JP17H06360, JP17K05387, JP17KK0096, JP21H00046, JP21K03617: MNM, 20K04034: SI). L.A.Z. acknowledges financial support from CONACyT-280775 and UNAM-PAPIIT IN110618 grants, México. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 851435).We present a high-angular resolution (∼1″) and wide-field ( 2.′9×1.′9 ) image of the 1.3 mm continuum, CO(J = 2–1) and SiO(J = 5–4) line emissions toward an embedded protocluster, FIR 3, FIR 4, and FIR 5, in the Orion Molecular Cloud 2 obtained from the Atacama Large Millimeter/submillimeter Array. We identify 51 continuum sources, 36 of which are newly identified in this study. Their dust masses, projected sizes, and H2 gas number densities are estimated to be 3.8 × 10−5–1.1 × 10−2 M⊙, 290–2000 au, and 6.4 × 106–3.3 × 108 cm−3, respectively. The results of a Jeans analysis show that ∼80% of the protostellar sources and ∼15% of the prestellar sources are gravitationally bound. We identify 12 molecular outflows traced in the CO(J = 2–1) emission, six of which are newly detected. We spatially resolve shocked gas structures traced by the SiO(J = 5–4) emission in this region for the first time. We identify shocked gas originating from outflows and other shocked regions. These results provide direct evidence of an interaction between dust condensation, FIR 4, and an energetic outflow driven by HOPS-370 located within FIR 3. A comparison of the outflow dynamical timescales, fragmentation timescales, and protostellar ages shows that the previously proposed triggered star formation scenario in FIR 4 is not strongly supported. We also discuss the spatial distribution of filaments identified in our continuum image by comparing it with a previously identified hub-fiber system in the N2H+ line.Publisher PDFPeer reviewe

ALMA Fragmented Source Catalogue in Orion (FraSCO) I. Outflow interaction within an embedded cluster in OMC-2/FIR3, FIR4, and FIR5

We present a high angular resolution ($\sim1"$) and wide-field ($2'.9 \times 1'.9$) image of the 1.3-mm continuum, CO($J$ = 2--1) line, and SiO($J$ = 5--4) line emissions toward an embedded protocluster, FIR3, FIR4, and FIR5, in the Orion Molecular Cloud 2 obtained from the Atacama Large Millimeter/submillimeter Array (ALMA). We identify 51 continuum sources, 36 of which are newly identified in this study. Their dust masses, projected sizes, and $\mathrm{H_2}$ gas number densities are estimated to be $3.8 \times 10^{-5}$--$1.1 \times 10^{-2} \mathrm{M_{\odot}}$, 290--2000 au, and $6.4 \times 10^{6}$--$3.3 \times 10^{8}\,\mathrm{cm^{-3}}$, respectively. The results of a Jeans analysis show that $\sim80\,\%$ of the protostellar sources and $\sim15\,\%$ of the prestellar sources are gravitationally bound. We identify 12 molecular outflows traced in the CO($J$ = 2--1) emission, six of which are newly detected. We spatially resolve shocked gas structures traced by the SiO($J$ = 5--4) emission in this region for the first time. We identify shocked gas originating from outflows and other shocked regions. These results provide direct evidence of an interaction between a dust condensation, FIR4, and an energetic outflow driven by HOPS-370 located within FIR3. A comparison of the outflow dynamical timescales, fragmentation timescales, and protostellar ages shows that the previously proposed triggered star-formation scenario in FIR4 is not strongly supported. We also discuss the spatial distribution of filaments identified in our continuum image by comparing it with a previously identified hub-fiber system in the $\mathrm{N_2H^+}$ line.Comment: 45 pages, 24 figures, 2 figure sets, 2 animations, Accepted for publication in Ap

Detection of extragalactic argonium, ArH+, toward PKS 1830−211

Context. Argonium has recently been detected as a ubiquitous molecule in our Galaxy. Model calculations indicate that its abundance peaks at molecular fractions in the range of 10^(-4) to 10^(-3) and that the observed column densities require high values of the cosmic ray ionization rate. Therefore, this molecular cation may serve as an excellent tracer of the very diffuse interstellar medium (ISM), as well as an indicator of the cosmic ray ionization rate. Aims. We attempted to detect ArH+ in extragalactic sources to evaluate its diagnostic power as a tracer of the almost purely atomic ISM in distant galaxies. Methods. We obtained ALMA observations of a foreground galaxy at z = 0.89 in the direction of the lensed blazar PKS 1830−211. Results. Two isotopologs of argonium, ^(36)ArH+ and ^(38)ArH+, were detected in absorption along two different lines of sight toward PKS 1830−211, known as the SW and NE images of the background blazar. The argonium absorption is clearly enhanced on the more diffuse line of sight (NE) compared to other molecular species. The isotopic ratio ^(36)Ar/^(38)Ar is 3.46 ± 0.16 toward the SW image, i.e., significantly lower than the solar value of 5.5. Conclusions. Our results demonstrate the suitability of argonium as a tracer of the almost purely atomic, diffuse ISM in high-redshift sources. The evolution of the isotopic ratio with redshift may help to constrain nucleosynthetic scenarios in the early Universe

ALMA Fragmented Source Catalog in Orion (FraSCO). I. Outflow Interaction within an Embedded Cluster in OMC-2/FIR 3, FIR 4, and FIR 5

We present a high-angular resolution (∼1'') and wide-field () image of the 1.3 mm continuum, CO(J = 2–1) and SiO(J = 5–4) line emissions toward an embedded protocluster, FIR 3, FIR 4, and FIR 5, in the Orion Molecular Cloud 2 obtained from the Atacama Large Millimeter/submillimeter Array. We identify 51 continuum sources, 36 of which are newly identified in this study. Their dust masses, projected sizes, and H2 gas number densities are estimated to be 3.8 × 10−5–1.1 × 10−2 M⊙, 290–2000 au, and 6.4 × 106–3.3 × 108 cm−3, respectively. The results of a Jeans analysis show that ∼80% of the protostellar sources and ∼15% of the prestellar sources are gravitationally bound. We identify 12 molecular outflows traced in the CO(J = 2–1) emission, six of which are newly detected. We spatially resolve shocked gas structures traced by the SiO(J = 5–4) emission in this region for the first time. We identify shocked gas originating from outflows and other shocked regions. These results provide direct evidence of an interaction between dust condensation, FIR 4, and an energetic outflow driven by HOPS-370 located within FIR 3. A comparison of the outflow dynamical timescales, fragmentation timescales, and protostellar ages shows that the previously proposed triggered star formation scenario in FIR 4 is not strongly supported. We also discuss the spatial distribution of filaments identified in our continuum image by comparing it with a previously identified hub-fiber system in the N2H+ line

The CARMA-NRO Orion Survey : filament formation via collision-induced magnetic reconnection - the stick in Orion A

Funding: European Research Council via the ERC Synergy Grant ECOGAL (grant 855130) (R.S.K.). S. Suri acknowledges support from the European Research Council under the Horizon 2020 Framework Program via the ERC Consolidator Grant CSF-648405. R.J.S. acknowledges funding from an STFC ERF (grant ST/N00485X/1).A unique filament is identified in the Herschel maps of the Orion A giant molecular cloud. The filament, which we name the Stick, is ruler-straight and at an early evolutionary stage. Transverse position–velocity diagrams show two velocity components closing in on the Stick. The filament shows consecutive rings/forks in C18O (1−0) channel maps, which is reminiscent of structures generated by magnetic reconnection. We propose that the Stick formed via collision-induced magnetic reconnection (CMR). We use the magnetohydrodynamics code Athena++ to simulate the collision between two diffuse molecular clumps, each carrying an antiparallel magnetic field. The clump collision produces a narrow, straight, dense filament with a factor of >200 increase in density. The production of the dense gas is seven times faster than freefall collapse. The dense filament shows ring/fork-like structures in radiative transfer maps. Cores in the filament are confined by surface magnetic pressure. CMR can be an important dense-gas-producing mechanism in the Galaxy and beyond.Peer reviewe

CARMA-NRO Orion Survey. Filamentary structure as seen in C^(18)O emission

Context. We present an initial overview of the filamentary structure in the Orion A molecular cloud utilizing a high angular and velocity resolution C^(18)O(1–0) emission map that was recently produced as part of the CARMA-NRO Orion Survey. Aims. The main goal of this study is to build a credible method to study varying widths of filaments which has previously been linked to star formation in molecular clouds. Due to the diverse star forming activities taking place throughout its ~20 pc length, together with its proximity of 388 pc, the Orion A molecular cloud provides an excellent laboratory for such an experiment to be carried out with high resolution and high sensitivity. Methods. Using the widely-known structure identification algorithm, DisPerSE, on a three-dimensional (PPV) C18O cube, we identify 625 relatively short (the longest being 1.74 pc) filaments over the entire cloud. We studied the distribution of filament widths using FilChaP, a python package that we have developed and made publicly available. Results. We find that the filaments identified in a two square-degree PPV cube do not overlap spatially, except for the complex OMC-4 region that shows distinct velocity components along the line of sight. The filament widths vary between 0.02 and 0.3 pc depending on the amount of substructure that a filament possesses. The more substructure a filament has, the larger is its width. We also find that despite this variation, the filament width shows no anticorrelation with the central column density which is in agreement with previous Herschel observations

CARMA-NRO Orion Survey: Core Emergence and Kinematics in the Orion A Cloud

We have investigated the formation and kinematics of submillimeter (submm) continuum cores in the Orion A molecular cloud. A comparison between submm continuum and near-infrared extinction shows a continuum core detection threshold of A_V ~ 5–10 mag. The threshold is similar to the star formation extinction threshold of A_V ~ 7 mag proposed by recent work, suggesting a universal star formation extinction threshold among clouds within 500 pc to the Sun. A comparison between the Orion A cloud and a massive infrared dark cloud G28.37+0.07 indicates that Orion A produces more dense gas within the extinction range 15 mag ≾ A V ≾ 60 mag. Using data from the CARMA-NRO Orion Survey, we find that dense cores in the integral-shaped filament (ISF) show subsonic core-to-envelope velocity dispersion that is significantly less than the local envelope line dispersion, similar to what has been found in nearby clouds. Dynamical analysis indicates that the cores are bound to the ISF. An oscillatory core-to-envelope motion is detected along the ISF. Its origin is to be further explored

Star Formation in the Orion A Molecular Cloud

Stars are found to form along and at junctions of filaments within molecular clouds. Filaments are elongated structures that have higher densities compared to their diffuse surroundings. Their first sightings date back to photographic plate observations of Barnard (1910). With the advances in astronomical instrumentation, observatories such as the Herschel Space Observatory were able to produce high sensitivity images of molecular clouds throughout the Galaxy. These images revealed that molecular clouds are pervaded with filaments on all scales. Furthermore, the filaments observed with Herschel in all molecular clouds are found to have common physical properties such as their width, bringing up an important question: “Can the properties of filamentary structure be universal?” In this thesis, I focused on the most nearby high-mass star forming region, the Orion A molecular cloud, and investigated the properties of its filamentary structure. Orion A is one of the most studied regions in the Galaxy and its filamentary nature was first presented with a large scale 13CO map in a study by Bally et al. (1987). Throughout this I made use of two large scale mapping surveys; the CARMA-NRO Orion Survey (Kong et al. 2018) and the C+ Square Degree Project. I also made use of the Herschel column density and temperature maps of the region (Stutz & Kainulainen 2015). In order to study the properties of the filaments, I first employed a structure detection algorithm, Discrete Persistent Structures Extractor (DisPerSE, Sousbie 2011), and investigated its performance on synthetic datasets. I found that in cases of low dynamic range and high levels of noise, DisPerSE can create artificial networks of filaments. Moreover, I developed a python based package, the Filament Characterization Package (FilChaP), that takes 2-dimensional (2D) or 3-dimensional (3D) datasets and DisPerSE filaments, and returns filament properties. FilChaP calculates filament length, width, skewness, kurtosis and curvature and is freely available for the community on github. Using FilChaP, I have investigated filament properties in different tracers (12CO, 13CO, C18O, [Cii]and dust column density). I found that filaments seen in C18O emission have a common width of 0.1 pc. The filament widths are independent from their central column densities, line masses and velocity dispersions. The majority of the dense cores are formed along the most gravitationally unstable filaments. I also found that the filaments are highly substructured and these substructures contribute to the turbulent velocity dispersion that provides support to the filaments and keeps them at a relatively constant width. This study revealed that, when calculating filament properties, it is important to separate structures along the line of sight by their velocities. In cases of filament widths calculated on the C18O integrated emission and dust column density maps, I found deviations from those filament widths calculated using the C18O datacube. These deviations are purely caused by the fact that integrated emission and column density maps cannot distinguish nearby structures or structures along the same line-of-sight at different velocities. Finally, I have looked at the [C ii] emission that mainly outlines the stellar feedback in the region. By comparing the radial profiles of C18O, 13CO, dust column density and [C ii] , I found that [C ii] emission almost always surrounds the emission from the dense gas indicating a chemical layering of different species that is typical for clumpy photo-dissociation regions