scholarly journals The Ophiuchus DIsc Survey Employing ALMA (ODISEA)–III: the evolution of substructures in massive discs at 3-5 au resolution

2020 ◽  
Author(s):  
Lucas A Cieza ◽  
Camilo González-Ruilova ◽  
Antonio S Hales ◽  
Paola Pinilla ◽  
Dary Ruíz-Rodríguez ◽  
...  
Keyword(s):  
Giant Planets ◽  
Evolutionary Sequence ◽  
Star Forming ◽  
Long Baseline ◽  
Large Program ◽  
Radial Profiles ◽  
Demographic Study ◽  
Dust Evolution ◽  
Small Dust ◽  
Good Agreement

Abstract We present 1.3 mm continuum ALMA long-baseline observations at 3-5 au resolution of 10 of the brightest discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project. We identify a total of 26 narrow rings and gaps distributed in 8 sources and 3 discs with small dust cavities (r <10 au). We find that two discs around embedded protostars lack the clear gaps and rings that are ubiquitous in more evolved sources with Class II SEDs. Our sample includes 5 objects with previously known large dust cavities (r >20 au). We find that the 1.3 mm radial profiles of these objects are in good agreement with those produced by numerical simulations of dust evolution and planet-disc interactions, which predict the accumulation of mm-sized grains at the edges of planet-induced cavities. Our long-baseline observations resulted in the largest sample of discs observed at ∼3-5 au resolution in any given star-forming region (15 objects when combined with Ophiuchus objects in the DSHARP Large Program) and allow for a demographic study of the brightest $\sim 5\%$ of the discs in Ophiuchus (i.e. the most likely formation sites of giant planets in the cloud). We use this unique sample to propose an evolutionary sequence and discuss a scenario in which the substructures observed in massive protoplanetary discs are mainly the result of planet formation and dust evolution. If this scenario is correct, the detailed study of disc substructures might provide a window to investigate a population of planets that remains mostly undetectable by other techniques.

scholarly journals Planetary nebula abundances in dwarf galaxies

2015 ◽  
Vol 11 (A29B) ◽  
Author(s):  
Denise R. Gonçalves
Keyword(s):  
Chemical Evolution ◽  
Planetary Nebula ◽  
Stellar Population ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Mass Range ◽  
Evolutionary Sequence ◽  
Star Forming ◽  
The Past ◽  
Good Agreement

AbstractThe framework of the present review is as follows. The Local Group (LG) is populated by dwarf galaxies belonging to different morphological types. Apparently these galaxies are very different. The questions naturally raised from this framework are many. Is there an evolutionary sequence among them? Do they share common progenitors? Is the environment at the origin of their differences? The method we propose to answer to these questions is by investigating the chemical evolution of dwarf galaxies and their mass-metallicity relation (MZR). To this aim we use metallicities derived from planetary nebulae, since this stellar population is present in the star-forming (dwarf irregular, dIrr) as well as in the quiescent (dwarf spheroidal, dSph) galaxies. The results, actually, show that both dIrr and dSph galaxies of the LG follow the same MZR, at variance with the differences claimed in the past. These results are in good agreement with the recently derived MZR, based on stellar instead of the nebular metallicities of the LG dwarf galaxies. Moreover, our MZR is also consistent with the global MZR of SLOAN star-forming galaxies, which spans a wider stellar mass range (~ 106 - 1011 M⊙) than the LG dwarfs.

scholarly journals Dust evolution in the star forming turbulent interstellar medium

2006 ◽  
Vol 2 (S237) ◽  
pp. 47-52
Author(s):  
François Boulanger
Keyword(s):  
Interstellar Medium ◽  
Interstellar Dust ◽  
Dust Particles ◽  
Interstellar Clouds ◽  
Star Forming ◽  
Interstellar Turbulence ◽  
Star Forming Regions ◽  
Potential Impact ◽  
Dust Evolution ◽  
Small Dust

AbstractUnderstanding interstellar dust evolution is a major challenge underlying the interpretation of Spitzer observations of interstellar clouds, star forming regions and galaxies. I illustrate on-going work along two directions. I outline the potential impact of interstellar turbulence on the abundance of small dust particles in the diffuse interstellar medium and translucent sections of molecular clouds. I present results from an analysis of ISO and Spitzer observations of the central part of 30 Doradus, looking for dust evolution related to the radiative and dynamical impact of the R136 super star cluster on its parent molecular cloud.

scholarly journals Giant Molecular Cloud Formation at the Interface of Colliding Supershells in the Large Magellanic Cloud

2021 ◽  
Author(s):  
Kosuke Fujii ◽  
Norikazu Mizuno ◽  
J R Dawson ◽  
Tsuyoshi Inoue ◽  
Kazufumi Torii ◽  
...  
Keyword(s):  
Large Magellanic Cloud ◽  
Cloud Formation ◽  
Beam Size ◽  
Star Forming ◽  
Star Forming Regions ◽  
Long Baseline ◽  
Gravitational Instabilities ◽  
Atomic Medium ◽  
High Column ◽  
Compact Array

Abstract We investigate the H i envelope of the young, massive GMCs in the star-forming regions N48 and N49, which are located within the high column density H i ridge between two kpc-scale supergiant shells, LMC 4 and LMC 5. New long-baseline H i 21 cm line observations with the Australia Telescope Compact Array (ATCA) were combined with archival shorter baseline data and single dish data from the Parkes telescope, for a final synthesized beam size of 24.75″ by 20.48″, which corresponds to a spatial resolution of ∼ 6 pc in the LMC. It is newly revealed that the H i gas is highly filamentary, and that the molecular clumps are distributed along filamentary H i features. In total 39 filamentary features are identified and their typical width is ∼ 21 (8–49) [pc]. We propose a scenario in which the GMCs were formed via gravitational instabilities in atomic gas which was initially accumulated by the two shells and then further compressed by their collision. This suggests that GMC formation involves the filamentary nature of the atomic medium.

scholarly journals VLBA+GBT observations of the COSMOS field and radio source counts at 1.4 GHz

2018 ◽  
Vol 616 ◽  
pp. A128 ◽  
Author(s):  
N. Herrera Ruiz ◽  
E. Middelberg ◽  
A. Deller ◽  
V. Smolčić ◽  
R. P. Norris ◽  
...  
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Lower Limit ◽  
High Sensitivity ◽  
Host Galaxy ◽  
Radio Sources ◽  
Source Population ◽  
Star Forming ◽  
Brightness Temperatures ◽  
Long Baseline

We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of μJy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, meaning that it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z ≥ 0.1). On the other hand, this technique only allows us to positively identify when a radio-active AGN is present, in other words, we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, ten of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40−75% at flux density levels between 150 μJy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.

scholarly journals Water Masers Outburst in the Massive Stellar Cluster W49A

2015 ◽  
Vol 12 (S316) ◽  
pp. 155-156
Author(s):  
Busaba H. Kramer ◽  
Karl M. Menten ◽  
Tomasz Kamiński ◽  
Bo Zhang ◽  
Nimesh A. Patel ◽  
...  
Keyword(s):  
Stellar Cluster ◽  
Star Forming ◽  
Physical Conditions ◽  
Long Baseline ◽  
Major Flare ◽  
Multi Wavelength ◽  
Remarkable Result ◽  
Water Masers ◽  
Very Long Baseline Array ◽  
Very High

AbstractWe report a multi-wavelength study of a recent major flare (~ 80,000 Jy at VLSR ~ -98.1 km s−1) of the 22-GHz water maser in W49A. In February 2014, we started monthly monitoring with the Effelsberg 100-m radio telescope. In May 2014, we carried out the nearly simultaneous observations of the 22-GHz transition with selected submillimeter water transitions using the IRAM 30-m telescope (at 183 GHz) and the Atacama Pathfinder Experiment (APEX) 12-m telescope (from 321 to 475 GHz). We have also performed interferometric observations using the NRAO Very Long Baseline Array (VLBA) at 22 GHz and the Submillimeter Array (SMA) at 321 and 325 GHz. One remarkable result is the detection of very high velocity emission features in several transitions. Our data also represent its first detection of the 475-GHz water transition in a star-forming region. Studying these multiple masing transitions in conjunction with theoretical modeling of their excitation not only places strong constraints on the physical conditions of the masing gas but also allows us to study their association with the embedded massive stellar cluster in W49A.

scholarly journals VLBI observations of the G25.65+1.05 water maser superburst

2019 ◽  
Vol 491 (3) ◽  
pp. 4069-4075 ◽  
Author(s):  
R A Burns ◽  
G Orosz ◽  
O Bayandina ◽  
G Surcis ◽  
M Olech ◽  
...  
Keyword(s):  
Path Length ◽  
Massive Star ◽  
Very Long Baseline Interferometry ◽  
Complex Structure ◽  
Rapid Onset ◽  
Line Of Sight ◽  
Star Forming ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Water Maser

ABSTRACT This paper reports observations of a 22 GHz water maser ‘superburst’ in the G25.65+1.05 massive star-forming region, conducted in response to an alert from the Maser Monitoring Organisation (M2O). Very long baseline interferometry (VLBI) observations using the European VLBI Network (EVN) recorded a maser flux density of 1.2 × 104 Jy. The superburst was investipgated in the spectral, structural, and temporal domains and its cause was determined to be an increase in maser path length generated by the superposition of multiple maser emitting regions aligning in the line of sight to the observer. This conclusion was based on the location of the bursting maser in the context of the star-forming region, its complex structure, and its rapid onset and decay.

scholarly journals Spatially resolved signature of quenching in star-forming galaxies

2019 ◽  
Vol 490 (2) ◽  
pp. 2347-2366 ◽  
Author(s):  
Salvatore Quai ◽  
Lucia Pozzetti ◽  
Michele Moresco ◽  
Annalisa Citro ◽  
Andrea Cimatti ◽  
...  
Keyword(s):  
Star Formation ◽  
Gas Phase ◽  
Galaxy Evolution ◽  
Spatial Information ◽  
Formation Rate ◽  
Radial Profile ◽  
Control Sample ◽  
Star Forming ◽  
Radial Profiles ◽  
Two Samples

ABSTRACT Understanding when, how, and where star formation ceased (quenching) within galaxies is still a critical subject in galaxy evolution studies. Taking advantage of the new methodology developed by Quai et al. to select recently quenched galaxies, we explored the spatial information provided by the IFU data to get critical insights on this process. In particular, we analyse 10 SDSS-IV MaNGA galaxies that show regions with low [O iii]/H α compatible with a recent quenching of the star formation. We compare the properties of these 10 galaxies with those of a control sample of 8 MaNGA galaxies with ongoing star formation in the same stellar mass, redshift, and gas-phase metallicity range. The quenching regions found are located between 0.5 and 1.1 effective radii from the centre. This result is supported by the analysis of the average radial profile of the ionization parameter, which reaches a minimum at the same radii, while the one of the star-forming sample shows an almost flat trend. These quenching regions occupy a total area between ∼ 15 and 45 per cent of our galaxies. Moreover, the average radial profile of the star formation rate surface density of our sample is lower and flatter than that of the control sample, at any radii, suggesting a systematic suppression of the star formation in the inner part of our galaxies. Finally, the radial profiles of gas-phase metallicity of the two samples have a similar slope and normalization. Our results cannot be ascribed to a difference in the intrinsic properties of the analysed galaxies, suggesting a quenching scenario more complicated than a simple inside-out quenching.

scholarly journals The mass–metallicity and the fundamental metallicity relation revisited on a fully Te-based abundance scale for galaxies

2019 ◽  
Vol 491 (1) ◽  
pp. 944-964 ◽  
Author(s):  
Mirko Curti ◽  
Filippo Mannucci ◽  
Giovanni Cresci ◽  
Roberto Maiolino
Keyword(s):  
High Redshift ◽  
Formation Rate ◽  
Cosmic Time ◽  
Stellar Mass ◽  
Strong Line ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Theoretical Predictions ◽  
Galaxy Population ◽  
Good Agreement

ABSTRACT The relationships between stellar mass, gas-phase metallicity and star-formation rate (i.e. the mass–metallicity, MZR, and the fundamental metallicity relation, FMR) in the local Universe are revisited by fully anchoring the metallicity determination for SDSS galaxies on the Te abundance scale defined exploiting the strong-line metallicity calibrations presented by Curti et al. Self-consistent metallicity measurements allow a more unbiased assessment of the scaling relations involving M, Z and SFR, which provide powerful constraints for the chemical evolution models. We parametrize the MZR with a new functional form that allows us to better characterize the turnover mass. The slope and saturation metallicity are in good agreement with previous determinations of the MZR based on the Te method, while showing significantly lower normalization compared to those based on photoionization models. The Z–SFR dependence at fixed stellar mass is also investigated, being particularly evident for highly star-forming galaxies, where the scatter in metallicity is reduced up to a factor of ${\sim}30{{\ \rm per\ cent}}$. A new parametrization of the FMR is given by explicitly introducing the SFR dependence of the turnover mass into the MZR. The residual scatter in metallicity for the global galaxy population around the new FMR is 0.054 dex. The new FMR presented in this work represents a useful local benchmark to compare theoretical predictions and observational studies (of both local and high-redshift galaxies) whose metallicity measurements are tied to the abundance scale defined by the Te method, hence allowing proper assessment of its evolution with cosmic time.

scholarly journals Extended star-forming regions within galaxies in a dense proto-cluster core at z = 2.53†

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Tomoko L Suzuki ◽  
Yosuke Minowa ◽  
Yusei Koyama ◽  
Tadayuki Kodama ◽  
Masao Hayashi ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Structural Evolution ◽  
Cluster Core ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Star Formation Activity ◽  
Radial Profiles ◽  
Structural Growth ◽  
The One

Abstract At z ∼ 2, star formation activity is thought to be high even in high-density environments such as galaxy clusters and proto-clusters. One of the critical but outstanding issues is if the structural growth of star-forming galaxies can differ depending on their surrounding environments. In order to investigate how galaxies grow their structures and what physical processes are involved in the evolution of galaxies, one requires spatially resolved images of not only stellar components but also star-forming regions within galaxies. We conducted (Adaptive Optics) AO-assisted imaging observations for star-forming galaxies in a dense proto-cluster core at z = 2.53 with IRCS and AO188 mounted on the Subaru Telescope. A combination of AO and narrow-band filters allows us to obtain resolved maps of Hα-emitting regions with an angular resolution of ${0{^{\prime\prime}_{.}}1}$–${0{^{\prime\prime}_{.}}2}$, which corresponds to ∼1 kpc at z ∼ 2.5. Based on stacking analyses, we compare radial profiles of star-forming regions and stellar components and find that the star-forming region of a sub-sample with log (M*/$M_\odot$) ∼ 10–11 is more extended than the stellar component, indicating the inside-out growth of the structure. This trend is similar to the one for star-forming galaxies in general fields at z = 2–2.5 obtained with the same observational technique. Our results suggest that the structural evolution of star-forming galaxies at z = 2–2.5 is mainly driven by internal secular processes irrespective of surrounding environments.

Body Force Modeling of the Aerodynamics of the Fan of a Turbofan at Windmill

2016 ◽  
Author(s):  
Guillaume Dufour ◽  
William Thollet
Keyword(s):  
Experimental Data ◽  
Rotational Speed ◽  
Body Force ◽  
Ground Level ◽  
Cost Ratio ◽  
Present Contribution ◽  
Force Modeling ◽  
Radial Profiles ◽  
Bypass Ratio ◽  
Good Agreement

The windmilling regime of a turbofan corresponds to a freewheeling mode of the fan rotor, driven by the ram pressure at the inlet. Early in the design process, determination of the windmilling rotational speed of the fan can be critical in the design of the supporting structure of the engine. Therefore, prediction of key parameters in windmilling is an important part of engine design. In particular, given the very high bypass ratio obtained at windmill (typically around 50), the flow in the fan stage and bypass duct is of prime interest, as it drives the establishment of the rotational speed of the low pressure spool and the overall drag. Classical CFD simulations have been shown to provide an adequate representation of the flow, but extensive parametric studies can be needed, which underlines the need for reduced-cost modeling of the flow in the engine. In this context, a body force modeling (BFM) approach to windmilling simulations is examined in the present contribution. The main objective is to assess the capability of the BFM approach to reproduce the aerodynamics of the flow in the fan rotor of a turbofan at windmill, and to propose a method to predict the rotational speed of the fan. The test case considered is a high-bypass ratio geared turbofan (the DGEN 380), which has been tested in an experimental facility designed to reproduce ground level windmilling conditions. The available global and local experimental data are used to validate the model. Furthermore, classical RANS simulations are also provided as reference simulations to assess the accuracy of the BFM results. It is found that the overall performance of the fan is well predicted by the BFM simulations, in particular at the low rotational regime associated to windmilling. In terms of local validation, radial profiles are also found to be in good agreement, except close to the shroud. Analysis of the CFD results shows this can be traced back to massive flow separation in the rotor tip area. In terms of cost, a BFM simulation is about 80 times faster than the baseline CFD computation, making this approach very efficient in term of accuracy-to-cost ratio. Finally, assuming zero-work exchange across the rotor, a transient equation for the rotational speed is derived and included in the time-marching process to the steady state. As a result, the rotational speed of the fan becomes an output of the simulations. The rotational speed predicted by the present model shows good agreement with engine experimental data. However, as only the rotor is modeled, the internal losses are not fully accounted for, and the massflow has to be specified from the experimental data. Further improvement of the approach will consist in modeling the stator and the complete secondary duct so that the loss, and therefore the massflow, can be predicted.

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