L. V. Tóth

A giant ring-like structure at 0.78 <z <0.86 displayed by GRBs

According to the cosmological principle, Universal large-scale structure is homogeneous and isotropic. The observable Universe, however, shows complex structures even on very large scales. The recent discoveries of structures significantly exceeding the transition scale of 370 Mpc pose a challenge to the cosmological principle. We report here the discovery of the largest regular formation in the observable Universe; a ring with a diameter of 1720 Mpc, displayed by 9 gamma ray bursts (GRBs), exceeding by a factor of five the transition scale to the homogeneous and isotropic distribution. The ring has a major diameter of 43 o and a minor diameter of 30 o at a distance of 2770 Mpc in the 0.78 < z < 0.86 redshift range, with a probability of 2 × 10 6 of being the result of a random fluctuation in the GRB count rate. Evidence suggests that this feature is the projection of a shell onto the plane of the sky. Voids and string-like formations are common outcomes of large-scale structure. However, these structures have maximum sizes of 150 Mpc, which are an order of magnitude smaller than the observed GRB ring diameter. Evidence in support of the shell interpretation requires that temporal information of the transient GRBs be included in the analysis. This ring-shaped feature is large enough to contradict the cosmological principle. The physical mechanism responsible for causing it is unknown.

New data support the existence of the Hercules-Corona Borealis Great Wall

Context. Several large structures, including the Sloan Great Wall, the Huge Large Quasar Group, and a large gamma-ray burst cluster referred to as the Hercules-Corona Borealis Great Wall, appear to exceed the maximum structural size predicted by Universal inflationary models. The existence of very large structures such as these might necessitate cosmological model modifications. Aims. Gamma-ray bursts are the most luminous sources found in nature. They are associated with the stellar endpoints of massive stars and are found in and near distant galaxies. Since they are viable indicators of the dense part of the Universe containing normal matter, the spatial distribution of gamma-ray bursts can serve as tracers of Universal large-scale structure. Methods. An increased sample size of gamma-ray bursts with known redshift provides us with the opportunity to validate or invalidate the existence of the Hercules-Corona Borealis Great Wall. Nearest-neighbour tests are used to search the larger sample for evidence of clustering and a bootstrap point-radius method is used to estimate the angular cluster size. The potential influence of angular sampling biasing is studied to determine the viability of the results. Results. The larger gamma-ray burst database further supports the existence of a statistically significant gamma-ray burst cluster at 1.6 ≤ z < 2.1 with an estimated angular size of 2000–3000 Mpc. Conclusions. Although small number statistics limit our angular resolution and do not rule out the existence of adjacent and/or lineof-sight smaller structures, these structures must still clump together in order for us to see the large gamma-ray burst cluster detected here. This cluster provides support for the existence of very large-scale universal heterogeneities.

Galactic cold cores - VII. Filament formation and evolution: Methods and observational constraints

Context. The association of filaments with protostellar objects has made these structures a priority target in star formation studies. However, little is known about the link between filament properties and their local environment. Aims. The datasets from the Herschel Galactic Cold cores key programme allow for a statistical study of filaments with a wide range of intrinsic and environmental characteristics. Characterisation of this sample can therefore be used to identify key physical parameters and quantify the role of the environment in the formation of supercritical filaments. These results are necessary to constrain theoretical models of filament formation and evolution. Methods. Filaments were extracted from fields at distance D< 500 pc with the getfilaments  algorithm and characterised according to their column density profiles and intrinsic properties. Each profile was fitted with a beam-convolved Plummer-like function, and the filament structure was quantified based on the relative contributions from the filament “core”, represented by a Gaussian, and “wing” component, dominated by the power-law behaviour of the Plummer-like function. These filament parameters were examined for populations associated with different background levels. Results. Filaments increase their core (M_(line,core)) and wing (M_(line,wing)) contributions while increasing their total linear mass density (M_(line,tot)). Both components appear to be linked to the local environment, with filaments in higher backgrounds having systematically more massive M_(line,core) and M_(line,wing). This dependence on the environment supports an accretion-based model of filament evolution in the local neighbourhood (D ≤ 500 pc). Structures located in the highest backgrounds develop the highest central A_V, M_(line,core), and M_(line,wing) as M_(line,tot) increases with time, favoured by the local availability of material and the enhanced gravitational potential. Our results indicate that filaments acquiring a significantly massive central region with M_(line,core) ≳ M_(crit)/2 may become supercritical and form stars. This translates into a need for filaments to become at least moderately self-gravitating to undergo localised star formation or become star-forming filaments.

Structure and stability in TMC-1: Analysis of NH3molecular line andHerschelcontinuum data

Aims. We examined the velocity, density, and temperature structure of Taurus molecular cloud-1 (TMC-1), a filamentary cloud in a nearby quiescent star forming area, to understand its morphology and evolution. Methods. We observed high signal-to-noise (S/N), high velocity resolution NH 3 (1,1), and (2, 2) emission on an extended map. By fitting multiple hyperfine-split line profiles to the NH 3 (1, 1) spectra, we derived the velocity distribution of the line components and calculated gas parameters on several positions. Herschel SPIRE far-infrared continuum observations were reduced and used to calculate the physical parameters of the Planck Galactic Cold Clumps (PGCCs) in the region, including the two in TMC-1. The morphology of TMC-1 was investigated with several types of clustering methods in the parameter space consisting of position, velocity, and column density. Results. Our Herschel -based column density map shows a main ridge with two local maxima and a separated peak to the south-west. The H 2 column densities and dust colour temperatures are in the range of 0.5−3.3 × 10 22  cm -2 and 10.5−12 K, respectively. The NH 3 column densities and H 2 volume densities are in the range of 2.8−14.2 × 10 14  cm -2 and 0.4−2.8 × 10 4  cm -3 . Kinetic temperatures are typically very low with a minimum of 9 K at the maximum NH 3 and H 2 column density region. The kinetic temperature maximum was found at the protostar IRAS 04381+2540 with a value of 13.7 K. The kinetic temperatures vary similarly to the colour temperatures in spite of the fact that densities are lower than the critical density for coupling between the gas and dust phase. The k -means clustering method separated four sub-filaments in TMC-1 with masses of 32.5, 19.6, 28.9, and 45.9 M ⊙ and low turbulent velocity dispersion in the range of 0.13−0.2 km s -1 . Conclusions. The main ridge of TMC-1 is composed of four sub-filaments that are close to gravitational equilibrium. We label these TMC-1F1 through F4. The sub-filaments TMC-1F1, TMC-1F2, and TMC-1F4 are very elongated, dense, and cold. TMC-1F3 is a little less elongated and somewhat warmer, and probably heated by the Class I protostar, IRAS 04381+2540, which is embedded in it. TMC-1F3 is approximately 0.1 pc behind TMC1-F1. Because of its structure, TMC-1 is a good target to test filament evolution scenarios.

Galactic cold cores VIII. Filament formation and evolution: Filament properties in context with evolutionary models

Context. The onset of star formation is intimately linked with the presence of massive unstable filamentary structures. These filaments are therefore key for theoretical models that aim to reproduce the observed characteristics of the star formation process in the Galaxy. Aims. As part of the filament study carried out by the Herschel Galactic Cold Cores Key Programme, here we study and discuss the filament properties presented in GCC VII (Paper I) in context with theoretical models of filament formation and evolution. Methods. A conservatively selected sample of filaments located at a distance D< 500 pc was extracted from the GCC fields with the getfilaments algorithm. The physical structure of the filaments was quantified according to two main components: the central (Gaussian) region of the filament (core component), and the power-law-like region dominating the filament column density profile at larger radii (wing component). The properties and behaviour of these components relative to the total linear mass density of the filament and the column density of its environment were compared with the predictions from theoretical models describing the evolution of filaments under gravity-dominated conditions. Results. The feasibility of a transition from a subcritical to supercritical state by accretion at any given time is dependent on the combined effect of filament intrinsic properties and environmental conditions. Reasonably self-gravitating (high_(Mline,core)) filaments in dense environments (AV≳ 3 mag) can become supercritical on timescales of t ~ 1 Myr by accreting mass at constant or decreasing width. The trend of increasing M_(line,tot) (M_(line,core) and M_(line,wing)) and ridge AV with background for the filament population also indicates that the precursors of star-forming filaments evolve coevally with their environment. The simultaneous increase of environment and filament AV explains the observed association between dense environments and high M_(line,core) values, and it argues against filaments remaining in constant single-pressure equilibrium states. The simultaneous growth of filament and background in locations with efficient mass assembly, predicted in numerical models of filaments in collapsing clouds, presents a suitable scenario for the fulfillment of the combined filament mass−environment criterium that is in quantitative agreement with Herschel observations.

Galactic cold cores: IX. Column density structures and radiative-transfer modelling★★★

The Galactic Cold Cores (GCC) project has made Herschel observations of interstellar clouds where Planck detected compact sources of cold dust emission. Our aim is to characterise the structure of the clumps and their parent clouds. We also examine the accuracy to which the structure of dense clumps can be determined from submillimetre data. We use standard statistical methods to characterise the GCC fields. Clumps are extracted using column density thresholding and we construct for each field a three-dimensional radiative transfer (RT) model. These are used to estimate the relative radiation field intensities, clump stability, and the uncertainty of column density estimates. We examine the radial column density profiles of the clumps. In the GCC fields, the structure noise follows the relations previously established at larger scales. The fractal dimension has no significant dependence on column density and the values D = 1.25 +- 0.07 are only slightly lower than in typical molecular clouds. The column density PDFs exhibit large variations, e.g. in the case of externally compressed clouds. At scales r>0.1 pc, the radial column density distributions of the clouds follow an average relation of N~r^{-1}. In spite of a great variety of clump morphology, clumps tend to follow a similar N~r^{-1} relation below r~0.1 pc. RT calculations indicate only factor of 2.5 variation in the local radiation field intensity. The fraction of gravitationally bound clumps increases significantly in regions with A_V > 5 mag but most bound objects appear to be pressure-confined. The GCC host clouds have statistical properties similar to general molecular clouds. The gravitational stability, peak column density, and clump orientation are connected to the cloud background while most other statistics (e.g. D and radial profiles) are insensitive to the environment.

A selection of AKARI FIS BSC extragalactic objects

The point sources in the Bright Source Catalogue (BSC) of the AKARI Far– Infrared Surveyor (FIS) were classified based on their far–IR and mid–IR fluxes and colours using Quadratic Discriminant Analysis method (QDA) and Support Vector Machines (SVM). The reliability of our results show that we can successfully separate galactic and extragalactic AKARI point sources in the multidimensional space of fluxes and colours. However, differentiating among the extragalactic sub–types needs further information.