An all-sky Support Vector Machine selection of WISE YSO Candidates

We explored the AllWISE catalogue of the Wide-field Infrared Survey Explorer mission and identified Young Stellar Object candidates. Reliable 2MASS and WISE photometric data combined with Planck dust opacity values were used to build our dataset and to find the best classification scheme. A sophisticated statistical method, the Support Vector Machine (SVM) is used to analyse the multi-dimensional data space and to remove source types identified as contaminants (extragalactic sources, main sequence stars, evolved stars and sources related to the interstellar medium). Objects listed in the SIMBAD database are used to identify the already known sources and to train our method. A new all-sky selection of 133,980 Class I/II YSO candidates is presented. The estimated contamination was found to be well below 1% based on comparison with our SIMBAD training set. We also compare our results to that of existing methods and catalogues. The SVM selection process successfully identified >90% of the Class I/II YSOs based on comparison with photometric and spectroscopic YSO catalogues. Our conclusion is that by using the SVM, our classification is able to identify more known YSOs of the training sample than other methods based on colour-colour and magnitude-colour selection. The distribution of the YSO candidates well correlates with that of the Planck Galactic Cold Clumps in the Taurus--Auriga--Perseus--California region.Comment: 27 pages, 15 figures, 15 table

Fragmentation and kinematics of dense molecular cores in the filamentary infrared-dark cloud G011.11–0.12

We present new Plateau de Bure Interferometer observations of a region in the filamentary infrared-dark cloud (IRDC) G011.11-0.12 containing young, star-forming cores. In addition to the 3.2 mm continuum emission from cold dust, we map this region in the N2H+(1−0) line to trace the core kinematics with an angular resolution of 2′′ and velocity resolution of 0.2 km s-1. These data are presented in concert with recent Herschel results, single-dish N2H+(1−0) data, SABOCA 350 μm continuum data, and maps of the C18O (2−1) transition obtained with the IRAM 30 m telescope. We recover the star-forming cores at 3.2 mm continuum, while in N2H+ they appear at the peaks of extended structures. The mean projected spacing between N2H+ emission peaks is 0.18 pc, consistent with simple isothermal Jeans fragmentation. The 0.1 pc-sized cores have low virial parameters on the criticality borderline, while on the scale of the whole region, we infer that it is undergoing large-scale collapse. The N2H+ linewidth increases with evolutionary stage, while CO isotopologues show no linewidth variation with core evolution. Centroid velocities of all tracers are in excellent agreement, except in the starless region where two N2H+ velocity components are detected, one of which has no counterpart in C18O. We suggest that gas along this line of sight may be falling into the quiescent core, giving rise to the second velocity component, possibly connected to the global collapse of the region

Multi-scale analysis of the Monoceros OB 1 star-forming region. II. Colliding filaments in the Monoceros OB1 molecular cloud

Context. We started a multi-scale analysis of star formation in G202.3+2.5, an intertwined filamentary sub-region of the Monoceros OB molecular complex, in order to provide observational constraints o current theories and models that attempt to explain star formatio globally. In the first paper (Paper I), we examined the distributions o dense cores and protostars and found enhanced star formation activity i the junction region of the filaments. Aims: In this second paper we aim to unveil the connections between the core and filamen evolutions, and between the filament dynamics and the global evolutio of the cloud. Methods: We characterise the gas dynamics an energy balance in different parts of G202.3+2.5 using infrare observations from the Herschel and WISE telescopes and molecular tracer observed with the IRAM 30-m and TRAO 14-m telescopes. The velocity fiel of the cloud is examined and velocity-coherent structures ar identified, characterised, and put in perspective with the clou environment. Results: Two main velocity components are revealed, well separated in radial velocities in the north and merged around th location of intense N2H+ emission in the centre o G202.3+2.5 where Paper I found the peak of star formation activity. W show that the relative position of the two components along th sightline, and the velocity gradient of the N2H emission imply that the components have been undergoing collision fo 105 yr, although it remains unclear whether the gas move mainly along or across the filament axes. The dense gas wher N2H+ is detected is interpreted as the compresse region between the two filaments, which corresponds to a high mas inflow rate of 1 × 10-3 M☉ yr-1 an possibly leads to a significant increase in its star formatio efficiency. We identify a protostellar source in the junction regio that possibly powers two crossed intermittent outflows. We show that th H II region around the nearby cluster NCG 2264 is still expanding an its role in the collision is examined. However, we cannot rule out th idea that the collision arises mostly from the global collapse of th cloud. Conclusions: The (sub-)filament-scale observables examined in this paper reveal a collision between G202.3+2.5 sub-structures an its probable role in feeding the cores in the junction region. To she more light on this link between core and filament evolutions, one mus characterise the cloud morphology, its fragmentation, and magneti field, all at high resolution. We consider the role of the environmen in this paper, but a larger-scale study of this region is now necessar to investigate the scenario of a global cloud collapse. The reduce datacubes (FITS files) of our IRAM and TRAO observations are onl available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.f bin/cat/J/A+A/631/A

Formation of High-Mass stars in an isolated environment in the Large Magellanic Cloud

The aim of this study is to characterize the distribution and basic properties of the natal gas associated with high-mass young stellar objects (YSOs) in isolated environments in the Large Magellanic Cloud (LMC). High-mass stars usually form in Giant Molecular Clouds (GMCs) as part of a young stellar cluster, but some OB stars are observed far from GMCs. By examining the spatial coincidence between the high-mass YSOs and 12CO (J = 1-0) emission detected by NANTEN and Mopra observations, we selected ten high-mass YSOs that are located away from any of the NANTEN clouds but are detected by the Mopra pointed observations. The ALMA observations revealed that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with the high-mass YSOs, which indicates that these compact clouds are the sites of high-mass star formation. The high-density and high-temperature throughout the clouds are explained by the severe photodissociation of CO due to the lower metallicity than in the Galaxy. The star formation efficiency ranges from several to as high as ~ 40%, indicating efficient star formation in these environments. The enhanced turbulence may be a cause of the efficient star formation therein, as judged from the gas velocity information and the association with the lower density gas.Comment: 31 pages, 14 figures, PASJ accepted for publicatio

Galactic foreground of gamma-ray bursts from AKARI Far-Infrared Surveyor

We demonstrate the use of the AKARI FIS All-Sky Survey maps in the study of extragalactic objects. A quick but reliable estimate of the Galactic foreground is essential for extragalactic research in general. We explored the galactic foreground and calculated hydrogen column densities using AKARI FIS and other recent all-sky survey data, and compared our results to former estimates. Our AKARI-FIS-based foreground values were then used toward gamma-ray burst (GRB) sources as input for X-ray afterglow spectrum fitting. From those fits the intrinsic column densities at the GRB sources were derived. The high-angular-resolution AKARI-FIS-based Galactic foreground hydrogen column densities are statistically very similar, but for most of the tested directions somewhat lower than previous estimates based on low-resolution data. This is due to the low filling factor of high-density enhancements in all galactic latitudes. Accordingly, our AKARI-FIS-based new intrinsic hydrogen column densities are usually higher or similar compared to the values calculated based, e.g., on the low-resolution Leiden/Argentine/Bonn survey data and listed in the Leicester database. The variation, however, is typically smaller than the error of the estimate from the fits of the X-ray afterglow spectra. There are a number of directions where the improvement of the foreground estimates resulted in an overestimate of magnitude or higher increment of the derived intrinsic hydrogen column densities. We concluded that most of the GRBs with formerly extremely low intrinsic hydrogen column densities are in fact normal, but we confirmed that GRB050233 is indeed a non- enveloped long GRB