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Online carbon offset experiment -- students registering in a experimental study subject pool are rewarded with a lunch and decide on the type of lunch and whether in addition to buy a carbon offset or coffee. Causal effects of variation in menus, levels of carbon offset, and public visibility of the carbon offset are studied. This registration concerns the pilot data collection.

Our basic research question is the following: what are the effects of providing information about income distribution and the personal position/rank relative to others on satisfaction, happiness, attitudes, beliefs, preferences as well as labor and health outcomes? Similar questions have been asked by a number of world-class research teams in recent years (Card et al., 2012; Kuzmienko et al., 2015; Karadja et al., 2017; Perez Truglia, 2019; Bastani & Waldenström, 2019) but our specific contribution is to compare the causal effects of relative income information for several reference groups to which an individual belongs, such as their educational credential, occupation, birth cohort, municipality, including the nationwide comparison which has been typically used in many studies. To understand which relative income information is most relevant for the participants, we also have a treatment where subjects are free to choose to view one of several distributions. This treatment allows us to better evaluate which selection effects may be present in the field in situations where relative income information is freely available for those willing to search for it, and which effects the information is expected to have under those circumstances. A further contribution is to analyze the effects of relative income information on real behavior such as job mobility or charitable giving, in addition to satisfaction or intended behavior, combining information from the experiment with rich register data. We have previously pre-registered and run the associated pilot data collection and study. This is the pre-registration of the main data collection and main study.

We used the APEX telescope to observe the 372 GHz o-H$_2$D$^+(J_{K_a,\,K_c}=1_{1,\,0}-1_{1,\,1})$ line towards three prestellar cores and three protostellar cores in Orion B9. We also employed our previous APEX observations of C$^{17}$O, C$^{18}$O, N$_2$H$^+$, and N$_2$D$^+$ line emission, and 870 $\mu$m dust continuum emission towards the target sources. The o-H$_2$D$^+$ line was detected in all three prestellar cores, but in only one of the protostellar cores. The corresponding o-H$_2$D$^+$ abundances were derived to be $\sim(12-30)\times10^{-11}$ and $6\times10^{-11}$. Two additional spectral lines, DCO$^+(5-4)$ and N$_2$H$^+(4-3)$, were detected in the observed frequency bands with high detection rates of $100\%$ and $83\%$, respectively. The Orion B9 cores were found to be consistent with the relationship between the o-H$_2$D$^+$ abundance and gas temperature obeyed by other low-mass dense cores. The o-H$_2$D$^+$ abundance was found to decrease as the core evolves. The o-H$_2$D$^+$ abundances in the Orion B9 cores are in line with those found in other low-mass cores and larger than derived for high-mass star-forming regions. The higher o-H$_2$D$^+$ abundance in prestellar cores compared to that in cores hosting protostars is to be expected from chemical reactions where higher concentrations of gas-phase CO and elevated gas temperature accelerate the destruction of H$_2$D$^+$. The validity of using the [o-H$_2$D$^+$]/[N$_2$D$^+$] ratio as an evolutionary indicator, which has been proposed for massive clumps, remains to be determined when applied to these target cores. Overall, as located in a dynamic environment of Orion B, the Orion B9 filament provides an interesting target system to investigate the deuterium-based chemistry, and further observations of species like para-H$_2$D$^+$ and D$_2$H$^+$ would be of particular interest., Comment: 15 pages (incl. an appendix), 8 figures, 7 tables, accepted for publication in A&A, abstract abridged for arXiv

Physically unassociated background or foreground objects seen towards submillimetre sources are potential contaminants of both the studies of young stellar objects embedded in Galactic dust clumps and multiwavelength counterparts of submillimetre galaxies (SMGs). We employed the near-infrared and mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) and the submillimetre data from the Planck satellite, and uncovered a source, namely WISE J044232.92+322734.9, whose WISE infrared colours suggest that it is a star-forming galaxy (SFG), and which is seen in projection towards the Planck-detected dust clump PGCC G169.20-8.96. We used the MAGPHYS+photo-$z$ spectral energy distribution code to derive the photometric redshift and physical properties of J044232.92. The redshift was derived to be $z_{\rm phot}=1.132^{+0.280}_{-0.165}$, while, for example, the stellar mass, IR (8-1 000 $\mu$m) luminosity, and star formation rate were derived to be $M_{\star}=4.6^{+4.7}_{-2.5}\times10^{11}$ M$_{\odot}$, $L_{\rm IR}=2.8^{+5.7}_{-1.5}\times10^{12}$ L$_{\odot}$, and ${\rm SFR}=191^{+580}_{-146}$ ${\rm M}_{\odot}$ yr$^{-1}$. The derived value of $L_{\rm IR}$ suggests that J044232.92 could be an ultraluminous infrared galaxy, and we found that it is consistent with a main sequence SFG at a redshift of 1.132. Moreover, the estimated physical properties of J044232.92 are comparable to those of SMGs. Further observations, in particular high-resolution (sub-)millimetre and radio continuum imaging, are needed to better constrain the redshift and physical properties of J044232.92 and to see if the source really is a galaxy seen through a Galactic dust clump, in particular an SMG population member at $z\sim1.1$., Comment: 7 pages, 4 figures, 3 tables, accepted for publication in A&A, abstract abridged for arXiv

We used data from WISE, IRAS, and Herschel in conjuction with our previous observations with SABOCA and LABOCA, and constructed the far-IR to submillimetre spectral energy distributions (SEDs) of dense cores in the filamentary Seahorse infrared dark cloud (IRDC) G304.74+01.32. For the 12 analysed cores, which include two IR dark cores (no WISE counterpart), nine IR bright cores, and one HII region, the mean dust temperature of the cold (warm) component, the mass, luminosity, H$_2$ number density, and surface density were derived to be $13.3\pm1.4$ K ($47.0\pm5.0$ K), $113\pm29$ M$_{\odot}$, $192\pm94$ L$_{\odot}$, $(4.3\pm1.2)\times10^5$ cm$^{-3}$, and $0.77\pm0.19$ g cm$^{-3}$, respectively. The HII region IRAS 13039-6108a was found to be the most luminous source in our sample ($(1.1\pm0.4)\times10^3$ L$_{\odot}$). All the cores were found to be gravitationally bound (i.e. the virial parameter $\alpha_{\rm vir}0.4$ g cm$^{-3}$ derived for these seven cores also exceed the corresponding threshold for high-mass star formation. Five of the analysed cores (42%) show evidence of fragmentation into two components in the SABOCA 350 $\mu$m image. In addition to the HII region source IRAS 13039-6108a, some of the other cores in Seahorse also appear to be capable of giving birth to high-mass stars. The dense core population in the Seahorse IRDC has comparable average properties to the cores in the well-studied Snake IRDC G11.11-0.12. The Seahorse core fragmentation mechanisms appear to be heterogenous, including cases of both thermal and non-thermal Jeans instability. High-resolution follow-up studies are required to address the fragmented cores' genuine potential of forming high-mass stars., Comment: 16 pages (incl. two appendices), 9 figures, 6 tables, accepted for publication in A&A, abstract abridged for arXiv

We used the APEX telescope to observe spectral lines occurring at about 170 GHz frequency towards 14 positions along the full extent of the filamentary Seahorse infrared dark cloud. Six spectral line transitions were detected ($\geq3\sigma$) altogether, namely, SO$(N_J=4_4-3_3)$, H$^{13}$CN$(J=2-1)$, H$^{13}$CO$^+(J=2-1)$, SiO$(J=4-3)$, HN$^{13}$C$(J=2-1)$, and C$_2$H$(N=2-1)$. While SO, H$^{13}$CO$^+$, and HN$^{13}$C were detected in every source, the detection rates for C$_2$H and H$^{13}$CN were 92.9% and 85.7%, respectively. Only one source (SMM 3) showed detectable SiO emission (7.1% detection rate). Three clumps (SMM 5, 6, and 7) showed the SO, H$^{13}$CN, H$^{13}$CO$^+$, HN$^{13}$C, and C$_2$H lines in absorption. We found three positive correlations among the derived molecular abundances, of which those between C$_2$H and HN$^{13}$C and HN$^{13}$C and H$^{13}$CO$^+$ are the most significant (correlation coefficient $r\simeq0.9$). The statistically most significant evolutionary trends we uncovered are the drops in the C$_2$H abundance and in the $[{\rm HN^{13}C}]/[{\rm H^{13}CN}]$ ratio as the clump evolves from an IR dark stage to an IR bright stage and then to an HII region. The correlations we found between the different molecular abundances can be understood as arising from the gas-phase electron (ionisation degree) and atomic carbon abundances. The [C$_2$H] evolutionary indicator we found is in agreement with previous studies, and can be explained by the conversion of C$_2$H to other species (e.g. CO) when the clump temperature rises, especially after the ignition of a hot molecular core in the clump. The decrease of $[{\rm HN^{13}C}]/[{\rm H^{13}CN}]$ as the clump evolves is also likely to reflect the increase in the clump temperature, which leads to an enhanced formation of HCN and its $^{13}$C isotopologue., Comment: 23 pages (incl. an appendix), 13 figures, 7 tables, accepted for publication in A&A, abstract abridged for arXiv

Classification of young stellar objects (YSOs) into different evolutionary stages helps us to understand the formation process of new stars and planetary systems. Such classification has traditionally been based on spectral energy distributions (SEDs). An alternative approach is provided by supervised machine learning algorithms. We attempt to classify a sample of Orion YSOs into different classes, where each source has already been classified using multiwavelength SED analysis. We used 8 different learning algorithms to classify the target YSOs, namely a decision tree, random forest, gradient boosting machine (GBM), logistic regression, na\"ive Bayes classifier, $k$-nearest neighbour classifier, support vector machine, and neural network. The classifiers were trained and tested by using a 10-fold cross-validation procedure. As the learning features, we employed ten continuum flux densities spanning from the near-IR to submm. With a classification accuracy of 82% (with respect to the SED-based classes), a GBM algorithm was found to exhibit the best performance. The lowest accuracy of 47% was obtained with a na\"ive Bayes classifier. Our analysis suggests that the inclusion of the 3.6 $\mu$m and 24 $\mu$m flux densities is useful to maximise the YSO classification accuracy. Although machine learning has the potential to provide a rapid and fairly reliable way to classify YSOs, an SED analysis is still needed to derive the physical properties of the sources, and to create the labelled training data. The classification accuracies can be improved with respect to the present results by using larger data sets, more detailed missing value imputation, and advanced ensemble methods. Overall, the application of machine learning is expected to be very useful in the era of big astronomical data, for example to quickly assemble interesting target source samples for follow-up studies., Comment: 17 pages, 6 figures, 2 tables, accepted for publication in Astrophysics and Space Science, abstract abridged for arXiv

We mapped the filamentary infrared dark cloud (IRDC) G304.74+01.32 at 350 $\mu$m with the SABOCA bolometer. The new SABOCA data have a factor of 2.2 times higher resolution than our previous LABOCA 870 $\mu$m map of the cloud. We also employed the Herschel far-IR and submillimetre, and WISE IR data available for G304.74. The SABOCA data show that G304.74 is composed of a dense filamentary structure with a mean width of only $0.18\pm0.05$ pc. The percentage of LABOCA clumps that are found to be fragmented into SABOCA cores is $36\%\pm16\%$. The WISE data suggest that $65\%\pm18\%$ of the SABOCA cores host young stellar objects (YSOs). The mean dust temperature of the clumps, derived by comparing the Herschel/SPIRE flux densities, was found to be $15.0 \pm 0.8$ K. The mean mass, beam-averaged H$_2$ column density, and H$_2$ number density of the LABOCA clumps are estimated to be $55\pm10$ M$_{\odot}$, $(2.0\pm0.2)\times10^{22}$ cm$^{-2}$, and $(3.1\pm0.2)\times10^4$ cm$^{-3}$. The corresponding values for the SABOCA cores are $29\pm3$ M$_{\odot}$, $(2.9\pm0.3)\times10^{22}$ cm$^{-2}$, and $(7.9\pm1.2)\times10^4$ cm$^{-3}$. The G304.74 filament is estimated to be thermally supercritical by a factor of $\gtrsim3.5$ on the scale probed by LABOCA, and by a factor of $ \gtrsim1.5$ for the SABOCA filament. Our data strongly suggest that G304.74 has undergone hierarchical fragmentation. The IRDC G304.74 has a seahorse-like morphology in the Herschel images, and the filament appears to be attached by elongated, perpendicular striations. Besides the presence of perpendicularly oriented, dusty striations and potential embedded intermediate-mass YSOs, G304.74 is a relatively nearby ($d\sim2.5$ kpc) IRDC, which makes it a useful target for future star formation studies. Owing to its observed morphology, we propose that G304.74 could be nicknamed the Seahorse Nebula., Comment: 16 pages, 5 figures, 6 tables, accepted for publication in A&A, abstract abridged for arXiv

We present the VLA-COSMOS 3 GHz Large Project based on 384 hours of observations with the Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward the two square degree Cosmic Evolution Survey (COSMOS) field. The final mosaic reaches a median rms of 2.3 uJy/beam over the two square degrees at an angular resolution of 0.75". To fully account for the spectral shape and resolution variations across the broad (2 GHz) band, we image all data with a multiscale, multifrequency synthesis algorithm. We present a catalog of 10,830 radio sources down to 5 sigma, out of which 67 are combined from multiple components. Comparing the positions of our 3 GHz sources with those from the Very Long Baseline Array (VLBA)-COSMOS survey, we estimate that the astrometry is accurate to 0.01" at the bright end (signal-to-noise ratio, S/N_3GHz > 20). Survival analysis on our data combined with the VLA-COSMOS 1.4~GHz Joint Project catalog yields an expected median radio spectral index of alpha=-0.7. We compute completeness corrections via Monte Carlo simulations to derive the corrected 3 GHz source counts. Our counts are in agreement with previously derived 3 GHz counts based on single-pointing (0.087 square degrees) VLA data. In summary, the VLA-COSMOS 3 GHz Large Project simultaneously provides the largest and deepest radio continuum survey at high (0.75") angular resolution to date, bridging the gap between last-generation and next-generation surveys., 19 pages, 18 figures, 5 tables, accepted for publication in A&A

The star formation rate per unit area correlates well with the gas surface density for different types of galaxies. However, this Kennicutt-Schmidt law has not yet been examined for a large, homogeneously selected sample of SMGs, which could provide useful SF implementation information for models of massive galaxy formation and evolution. We aim at determining the K-S law parameters for the first time for a well-selected, statistical sample of SMGs. We used ALMA to conduct a 0.2" resolution, 870 $\mu$m imaging survey of 40 SMGs in COSMOS, which were initially selected at 1.1 mm. We analysed a sample of 32/40 target SMGs, for which our new ALMA 870 $\mu$m data provide information about the spatial extent of dust emission, and all of which have dust-obscured SFR and dust-based gas mass estimates available from our previous study. We divided our sample into equally large subsamples of main-sequence objects and starbursts, and found their K-S relations to be of the form $\Sigma_{\rm SFR} \propto \Sigma_{\rm gas}^{0.81\pm0.01}$ and $\Sigma_{\rm SFR} \propto \Sigma_{\rm gas}^{0.84\pm0.39}$, respectively. The slightly sub-linear K-S slopes we derived suggest that the SF efficiency is nearly constant across the $\Sigma_{\rm gas}$ range probed. Under the assumption of a Galactic CO-to-H$_2$ conversion factor for the whole sample, the MS SMGs obey a constant global SFE of about 21% per 100 Myr, while that of starburst SMGs is about 27%. The corresponding gas depletion times are $\sim480$ Myr and 370 Myr. On average, our SMGs have $\Sigma_{\rm gas}\gtrsim10^{3.9}$ M$_{\odot}$ pc$^{-2}$, which suggests that they are Eddington-limited. This is consistent with the theoretical expectation of a linear K-S relation for such systems. However, size measurements of the CO-emitting regions of SMGs, and the $\alpha_{\rm CO}$ values of SMGs are needed to further constrain their $\Sigma_{\rm gas}$ values., Comment: Accepted for publication in A&A Letters; 4 pages, 1 figure, plus 3 appendices with 3 figures and 2 tables

We carried out targeted ALMA observations of 129 fields in the COSMOS region at 1.25 mm, detecting 152 galaxies at S/N$\geq$5 with an average continuum RMS of 150 $��$Jy. These fields represent a S/N-limited sample of AzTEC / ASTE sources with 1.1 mm S/N$\geq$4 over an area of 0.72 square degrees. Given ALMA's fine resolution and the exceptional spectroscopic and multiwavelength photometric data available in COSMOS, this survey allows us unprecedented power in identifying submillimeter galaxy counterparts and determining their redshifts through spectroscopic or photometric means. In addition to 30 sources with prior spectroscopic redshifts, we identified redshifts for 113 galaxies through photometric methods and an additional nine sources with lower limits, which allowed a statistically robust determination of the redshift distribution. We have resolved 33 AzTEC sources into multi-component systems and our redshifts suggest that nine are likely to be physically associated. Our overall redshift distribution peaks at $z\sim$2.0 with a high redshift tail skewing the median redshift to $\tilde{z}$=2.48$\pm$0.05. We find that brighter millimeter sources are preferentially found at higher redshifts. Our faintest sources, with S$_{1.25 \rm mm}$1.8 mJy, have a median redshift of $\tilde{z}$=3.08$\pm$0.17. After accounting for spectral energy distribution shape and selection effects these results are consistent with several previous submillimeter galaxy surveys, and moreover, support the conclusion that the submillimeter galaxy redshift distribution is sensitive to survey depth., Accepted for publication in Astronomy & Astrophysics for review 17 pages in body + 26 in appendices

We determine the radio size distribution of a large sample of 152 SMGs in COSMOS that were detected with ALMA at 1.3 mm. For this purpose, we used the observations taken by the VLA-COSMOS 3 GHz Large Project. One hundred and fifteen of the 152 target SMGs were found to have a 3 GHz counterpart. The median value of the major axis FWHM at 3 GHz is derived to be $4.6\pm0.4$ kpc. The radio sizes show no evolutionary trend with redshift, or difference between different galaxy morphologies. We also derived the spectral indices between 1.4 and 3 GHz, and 3 GHz brightness temperatures for the sources, and the median values were found to be $\alpha=-0.67$ and $T_{\rm B}=12.6\pm2$ K. Three of the target SMGs, which are also detected with the VLBA, show clearly higher brightness temperatures than the typical values. Although the observed radio emission appears to be predominantly powered by star formation and supernova activity, our results provide a strong indication of the presence of an AGN in the VLBA and X-ray-detected SMG AzTEC/C61. The median radio-emitting size we have derived is 1.5-3 times larger than the typical FIR dust-emitting sizes of SMGs, but similar to that of the SMGs' molecular gas component traced through mid-$J$ line emission of CO. The physical conditions of SMGs probably render the diffusion of cosmic-ray electrons inefficient, and hence an unlikely process to lead to the observed extended radio sizes. Instead, our results point towards a scenario where SMGs are driven by galaxy interactions and mergers. Besides triggering vigorous starbursts, galaxy collisions can also pull out the magnetised fluids from the interacting disks, and give rise to a taffy-like synchrotron-emitting bridge. This provides an explanation for the spatially extended radio emission of SMGs, and can also cause a deviation from the well-known IR-radio correlation., Comment: 32 pages (incl. 5 appendices), 17 figures, 7 tables; accepted for publication in A&A; abstract abridged for arXiv

We characterise the physical nature of a 1.1 mm-selected, flux-limited, and interferometrically followed up sample of SMGs in COSMOS. We used the MAGPHYS code to fit the multiwavelength (UV-radio) SEDs of 16 of the target SMGs. We also constructed the pure radio SEDs of our SMGs using three different radio bands (325 MHz, 1.4 GHz, and 3 GHz). Moreover, since two SMGs in our sample, AzTEC1 and AzTEC3, benefit from previous CO line observations, we studied their properties in more detail. We found that 63% of our target SMGs lie above the galaxy main-sequence by more than a factor of 3, and hence are starbursts. The 3 GHz radio sizes we have previously measured for the target SMGs were compared with the present stellar mass estimates, and we found that the z>3 SMGs are fairly consistent with the mass-size relationship of z~2 compact, quiescent galaxies (cQGs). The median IR-radio correlation parameter is found to be q=2.27, which is lower than measured locally (median q=2.64). AzTEC1 is found to have a sub-Eddington SFR surface density (by a factor of 2.6), while AzTEC3 appears to be an Eddington-limited starburster. The gas reservoir in these two high-z SMGs would be exhausted in only ~86 and 19 Myr at the current SFR, respectively. A comparison of the MAGPHYS-based properties of our SMGs with those of equally bright ALESS SMGs suggests that the two populations share fairly similar physical characteristics, including the q parameter. A hint of negative correlation is found between the 3 GHz size and the level of starburstiness, and hence cosmic-ray electrons in more compact starbursts might be more susceptible to free-free absorption. Some of the derived low and high q values (compared to the local median) could be the result of a specific merger/post-starburst phase of galaxy evolution. Overall, our results support the scenario where z>3 SMGs evolve into today's giant ellipticals., 26 pages (incl. 4 appendices), 13 figures, 8 tables; accepted for publication in A&A; abstract abridged for arXiv

We present observations with the Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward a sub-field of the XXL-North 25 deg2 field targeting the first supercluster discovered in the XXL Survey. The structure has been found at a spectroscopic redshift of 0.43 and extending over 0.̊35 × 0.̊1 on the sky. The aim of this paper is twofold. First, we present the 3 GHz VLA radio continuum observations, the final radio mosaic and radio source catalogue, and, second, we perform a detailed analysis of the supercluster in the optical and radio regimes using photometric redshifts from the CFHTLS survey and our new VLA-XXL data. Our final 3 GHz radio mosaic has a resolution of 3.̋2 × 1.̋9, and encompasses an area of 41' × 41' with rms noise level lower than ~ 20 μJy beam-1. The noise in the central 15' × 15' region is ≈ 11 μJy beam-1. From the mosaic we extract a catalogue of 155 radio sources with signal-to-noise ratio (S/N) ≥ 6, eight of which are large, multicomponent sources, and 123 (79%) of which can be associated with optical sources in the CFHTLS W1 catalogue. Applying Voronoi tessellation analysis (VTA) in the area around the X-ray identified supercluster using photometric redshifts from the CFHTLS survey we identify a total of seventeen overdensities at zphot = 0.35 - 0.50, 7 of which are associated with clusters detected in the XMM-Newton XXL data. We find a mean photometric redshift of 0.43 for our overdensities, consistent with the spectroscopic redshifts of the brightest cluster galaxies of seven X-ray detected clusters. The full VTA-identified structure extends over ~ 0.̊6 × 0.̊2 on the sky, which corresponds to a physical size of ~ 12 × 4 Mpc2 at z = 0.43. No large radio galaxies are present within the overdensities, and we associate eight (S/N> 7) radio sources with potential group/cluster member galaxies. The spatial distribution of the red and blue VTA-identified potential group member galaxies, selected by their observed g - r colours, suggests that the clusters are not virialised yet, but are dynamically young, as expected for hierarchical structure growth in a ΛCDM universe. Further spectroscopic data are required to analyse the dynamical state of the groups. The full catalogue is available as a queryable database table XXL_VLA_15 via the XXL Master Catalogue browser http://cosmosdb.iasf-milano.inaf.it/XXL. A copy of the catalogue and the mosaic are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?IX/49A FITS file of the reduced image is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A8

The present study aims to characterise the physical and chemical properties of the protostellar core Orion B9-SMM3. The APEX telescope was used to perform a follow-up molecular line survey of SMM3. The following species were identified from the frequency range 218.2-222.2 GHz: $^{13}$CO, C$^{18}$O, SO, para-H$_2$CO, and E$_1$-type CH$_3$OH. The on-the-fly mapping observations at 215.1-219.1 GHz revealed that SMM3 is associated with a dense gas core as traced by DCO$^+$ and p-H$_2$CO. Altogether three different p-H$_2$CO transitions were detected with clearly broadened linewidths (8.2-11 km s$^{-1}$ in FWHM). The derived p-H$_2$CO rotational temperature, $64\pm15$ K, indicates the presence of warm gas. We also detected a narrow p-H$_2$CO line (FWHM=0.42 km s$^{-1}$) at the systemic velocity. The p-H$_2$CO abundance for the broad component appears to be enhanced by two orders of magnitude with respect to the narrow line value ($\sim3\times10^{-9}$ versus $\sim2\times10^{-11}$). The detected methanol line shows a linewidth similar to those of the broad p-H$_2$CO lines, which indicates their coexistence. The CO isotopologue data suggest that the CO depletion factor decreases from $\sim27\pm2$ towards the core centre to a value of $\sim8\pm1$ towards the core edge. In the latter position, the N$_2$D$^+$/N$_2$H$^+$ ratio is revised down to $0.14\pm0.06$. The origin of the subfragments inside the SMM3 core we found previously can be understood in terms of the Jeans instability if non-thermal motions are taken into account. The estimated fragmentation timescale, and the derived chemical abundances suggest that SMM3 is a few times $10^5$ yr old, in good agreement with its Class 0 classification inferred from the spectral energy distribution analysis. The broad p-H$_2$CO and CH$_3$OH lines, and the associated warm gas provide the first clear evidence of a molecular outflow driven by SMM3., 25 pages, 6 figures, 4 tables; accepted for publication in Astrophysics and Space Science

We study the environment of 23 submillimetre galaxies (SMGs) drawn from the JCMT/AzTEC 1.1mm S/N-limited sample in the COSMOS field, as well as 4 COSMOS SMGs at z_spec>4.5, and 1 at z_spec=2.49, yielding a sample of 28 SMGs. We search for overdensities using the COSMOS photometric redshifts based on over 30 UV-NIR photometric bands, reaching an accuracy of sigma(Delta z/(1+z))=0.0067 (0.0155) at z3.5). To identify overdensities we apply the Voronoi tessellation analysis, and estimate the overdensity estimator delta_g as a function of distance from the SMG and/or overdensity center. We test and validate our approach via simulations, X-ray detected groups, and spectroscopic verifications using VUDS and zCOSMOS catalogues showing that even with photometric redshifts in COSMOS we can efficiently retrieve overdensities out to z~5. Our results yield that 11/23 (48%) JCMT/AzTEC 1.1mm SMGs occupy overdense environments. Considering the entire JCMT/AzTEC 1.1mm S/N>4 sample, and accounting for the expected fraction of spurious detections, yields that 35-61% of the SMGs in the S/N-limited sample occupy overdense environments. We perform an X-ray stacking analysis in the 0.5-2keV band using a 32" aperture and our SMG positions, and find statistically significant detections. For our z2] subsample we find an average flux of (4.0+/-0.8)x10^{-16} [(1.3+/-0.5)x10^{-16}] erg/s/cm^2 and a corresponding total mass of M_200 = 2.8x10^{13} [2x10^{13}] MSol. Our results suggest a higher occurrence of SMGs occupying overdense environments at z>3, than at z, 21 pages, 3 figures, 8 tables; accepted for publication in A&A

The aim of this study is to investigate the nature of radio sources associated with young stellar objects (YSOs) belonging to the R CrA cluster. By combining the centimetre radio data with the wealth of shorter wavelength data accumulated recently we wish to refine estimates of the evolutionary stages of the YSOs. Fluxes and spectral indices for the brightest radio sources were derived from the observations at 3, 6, and 20 cm using the ATCA. Seven of detected sources can be assigned to YSOs, which have counterparts in the X-rays, infrared or submm. One of the YSOs, Radio Source 9, is a Class 0 candidate, and another, IRS 7B, is suggested to be in the Class 0/I transition stage. IRS 7B is associated with extended radio lobes at 6 and 20 cm. The lobes may have a gyrosynchrotron emission component, which could be understood in terms of Fermi accleration in shocks. The Class I objects detected here seem to be a mixed lot. One of these, the wide binary IRS 5, shows a negative spectral index, rapid variability, and a high degree of circular polarisation with $V/I\approx33$ % on one of the days of observation. These signs of magnetic activity suggest that at least one of the binary components has advanced beyond the Class I stage. The radio source without YSO assigment, Radio Source 5, has been suggested to be a brown dwarf. The radio properties, in particular its persistent strong emission, do not support this classification. The radio characteristics of the detected YSOs roughly agree with the scheme where the dominant emission mechanism changes with age. The heterogeneity of the Class I group can possibly be explained by a drastic decline in the jet activity during this stage, which also changes the efficiency of free-free absorption around the protostar.

Radio emission at cm wavelengths from highly star-forming galaxies, such as SMGs, is dominated by synchrotron radiation arising from supernova activity. Using deep, high-resolution ($1\sigma=2.3$ $\mu$Jy beam$^{-1}$; $0.75^{"}$) cm radio-continuum observations taken by the VLA-COSMOS 3 GHz Large Project, we studied the radio-emitting sizes of a flux-limited sample of SMGs in the COSMOS field. Of the 39 SMGs studied here, 3 GHz emission was detected towards 18 of them ($\sim46\pm11\%$) with S/N ratios in the range of ${\rm S/N=4.2-37.4}$. Using 2D elliptical Gaussian fits, we derived a median deconvolved major axis FWHM size of $0.54^{"}\pm 0.11^{"}$ for our 18 SMGs detected at 3 GHz. For the 15 SMGs with known redshift we derived a median linear major axis FWHM of $4.2\pm0.9$ kpc. No clear correlation was found between the radio-emitting size and the 3 GHz or submm flux density, or the redshift of the SMG. However, there is a hint of larger radio sizes at $z\sim2.5-5$ compared to lower redshifts. The sizes we derived are consistent with previous SMG sizes measured at 1.4 GHz and in mid-$J$ CO emission, but significantly larger than those seen in the (sub)mm continuum emission. One possible scenario is that SMGs have i) an extended gas component with a low dust temperature, and which can be traced by low- to mid-$J$ CO line emission and radio continuum emission, and ii) a warmer, compact starburst region giving rise to the high-$J$ line emission of CO, which could dominate the dust continuum size measurements. Because of the rapid cooling of CR electrons in dense starburst galaxies ($\sim10^4-10^5$ yr), the more extended synchrotron radio-emitting size being a result of CR diffusion seems unlikely. Instead, if SMGs are driven by galaxy mergers the radio synchrotron emission might arise from more extended magnetised ISM around the starburst region., Comment: 18 pages (incl. 5 appendices), 7 figures, and 5 tables; accepted for publication in A&A; abstract abridged for arXiv

We used the PdBI to map a sample of 15 SMGs in the COSMOS field at the wavelength of 1.3 mm. The target SMGs were originally discovered in the JCMT/AzTEC 1.1 mm continuum survey at S/N=4-4.5. This paper presents, for the first time, interferometric millimetre-wavelength observations of these sources. The angular resolution of our observations, 1.8", allowed us to accurately determine the positions of the target SMGs. Using a detection threshold of S/N>4.5 regardless of multiwavelength counterpart association, and 4, Comment: 31 pages (incl. 5 appendices with 3 figures and 1 table), 6 figures and 4 tables in the main text. Accepted for publication in A&A

Aims. The main goal of the present study is to determine the fractional SiO abundance in high-mass star-forming cores, and to investigate its dependence on the physical conditions. In this way we wish to provide constraints on the chemistry models concerning the formation of SiO in the gas phase or via grain mantle evaporation. The work addresses also CH3CCH chemistry as the kinetic temperature is determined using this molecule. Methods. We estimate the physical conditions of 15 high-mass star-forming cores and derive the fractional SiO and CH3CCH abundances in them by using spectral line and dust continuum observations with the SEST. Results. The kinetic temperatures as derived from CH3CCH range from 25 to 39 K. The SiO emission regions are extended and typically half of the integrated line emission comes from the velocity range traced out by CH3CCH emission. The upper limit of SiO abundance in this 'quiescent' gas component is ~10^-10. The average CH3CCH abundance is about 7 x 10^-9. It shows a shallow, positive correlation with the temperature, whereas SiO shows the opposite tendency. Conclusions. We suggest that the high CH3CCH abundance and its possible increase when the clouds get warmer is related to the intensified desorption of the chemical precursors of the molecule from grain surfaces. In contrast, the observed tendency of SiO does not support the idea that the evaporation of Si-containing species from the grain mantles would be important, and it contradicts with the models where neutral reactions with activation barriers dominate the SiO production. A possible explanation for the decrease is that warmer cores represent more evolved stages of core evolution with fewer high-velocity shocks and thus less efficient SiO replenishment., Comment: 19 pages with 6 figures, accepted for publication in Astronomy & Astrophysics

Aims. The purpose of this study is to examine the prediction that the deuterated H + 3 ion, H 2 D + , can be found exclusively in the coldest regions of molecular cloud cores. This is also a feasibility study for the detection of the ground-state line of ortho-H 2 D + at 372 GHz with APEX. Methods. The (1 10 → 1 11 ) transition of H 2 D + at 372 GHz was searched towards selected positions in the massive star forming cloud OriB9, in the dark cloud L183, and in the low-to intermediate mass star-forming cloud R CrA. Results. The line was detected in cold, prestellar cores in the regions of OriB9 and L183, but only upper limits were obtained towards other locations which either have elevated temperatures or contain a newly born star. The H 2 D + detection towards OriB9 is the first one in a massive star-forming region. The fractional ortho-H 2 D + abundances (relative to H 2 ) are estimated to be ∼ 1 × 10 -10 in two cold cores in OriB9, and 3 x 10 -10 in the cold core of L183. Conclusions. The H 2 D + detection in OriB9 shows that also massive star forming regions contain very cold prestellar cores which probably have reached matured chemical composition characterized, e.g., by a high degree of deuterium fractionation. Besides as a tracer of the interior parts of prestellar cores, H 2 D + may therefore be used to put contraints on the timescales related to massive star formation.

Cha-MMS1 was mapped in the NH_3(1,1) line and the 1.2 cm continuum using the Australia Telescope Compact Array, ATCA. The angular resolution of the ATCA observations is 7'' (~ 1000 AU), and the velocity resolution is 50 m s^{-1}. The core was also mapped with the 64-m Parkes telesope in the NH_3(1,1) and (2,2) lines. Observations from Herschel Space Observatory and Spitzer Space telescope were used to help interpretation. A compact high column density core with a steep velocity gradient is detected in ammonia, with a fractional ammonia abundance compatible with determinations towards other dense cores. The direction of the velocity gradient agrees with previous single-dish observations, and the overall velocity distribution can be interpreted as rotation. The rotation axis goes through the position of a compact far-infrared source detected by Spitzer and Herschel. The specific angular momentum of the core is typical for protostellar envelopes. A string of 1.2 cm continuum sources is tentatively detected near the rotation axis. The ammonia spectra suggest the presence of warm embedded gas in its vicinity. An hourglass-shaped structure is seen in ammonia at the cloud's average LSR velocity, also aligned with the rotation axis. Although this structure resembles a pair of outflow lobes the ammonia spectra show no indications of shocked gas. The observed ammonia structure mainly delineates the inner envelope around the central source. The velocity gradient is likely to originate in the angular momentum of the contracting core, although influence of the outflow from the neighbouring young star IRS4 is possibly visible on one side of the core. The tentative continuum detection and the indications of a warm background component near the rotation axis suggest that the core contains a deeply embedded outflow which may have been missed in previous single-dish CO surveys owing to beam dilution., Comment: 15 pages, 12 figures. Submitted to Astronomy & Astrophysics

We present APEX observations of C17O(2-1), N2H+(3-2), and N2D+(3-2) towards the subfragments inside the prestellar core SMM 6 in Orion B9. We combined these spectral line data with our previous SABOCA 350-{\mu}m dust continuum map of the source. The subfragments are characterised by subsonic internal non-thermal motions ({\sigma}NT~0.5cs), and most of them appear to be gravitationally bound. The dispersion of the N2H+ velocity centroids among the condensations is very low (0.02 km/s). The CO depletion factors we derive, fD=0.8+/-0.4 - 3.6+/-1.5, do not suggest any significant CO freeze-out but this may be due to the canonical CO abundance we adopt. The fractional abundances of N2H+ and N2D+ with respect to H2 are found to be ~0.9-2.3x10^-9 and ~4.9-9.9x10^-10, respectively. The deuterium fractionation of N2H+, or the N2D+/N2H+ column density ratio, lies in the range 0.30+/-0.07 - 0.43+/-0.09. The detected substructure inside SMM 6 is likely the result of cylindrical Jeans-type gravitational fragmentation. We estimate the timescale for this fragmentation to be ~1.8x10^5 yr. The condensations are unlikely to be able to interact with one another and coalesce before local gravitational collapse ensues. Moreover, significant mass growth of the condensations via competitive-like accretion from the parent core seems unfeasible. The high level of molecular deuteration in the condensations suggests that gas-phase CO should be strongly depleted. It also points towards an advanced stage of chemical evolution. The subfragments of SMM 6 might therefore be near the onset of gravitational collapse, but whether they can form protostellar or substellar objects (brown dwarfs) depends on the local star formation efficiency and remains to be clarified., Comment: Accepted to A&A; 12 pages, 3 figures, 5 tables

We attempt to characterise the chemical properties of a sample of massive clumps of IRDCs through multi-molecular line observations. We also search for possible evolutionary trends among the derived chemical parameters. The clumps are studied using the MALT90 line survey data obtained with the Mopra telescope. The spectral-line data are used in concert with our previous LABOCA 870-$\mu$m dust emission data. Most of the detected species (SiO, C$_2$H, HNCO, HCN, HCO$^+$, HNC, HC$_3$N, and N$_2$H$^+$) show spatially extended emission towards many of the sources. The fractional abundances of the molecules are mostly found to be comparable to those determined in other recent similar studies of IRDC clumps. We found that the abundances of SiO, HNCO, and HCO$^+$ are higher in IR-bright clumps than in IR-dark sources, reflecting a possible evolutionary trend. A hint of such a trend is also seen for HNC and HC$_3$N. An opposite trend is seen for C$_2$H and N$_2$H$^+$. Moreover, a positive correlation is found between the abundances of HCO$^+$ and HNC, and between those of HNC and HCN. The HCN and HNC abundances also appear to increase as a function of the N$_2$H$^+$ abundance. The HNC/HCN and N$_2$H$^+$/HNC abundance ratios are derived to be ~1 on average, while that of HC$_3$N/HCN is ~10%. The N$_2$H$^+$/HNC ratio appears to increase as the clump evolves, while the HNC/HCO$^+$ ratio shows the opposite behaviour. The detected SiO emission is likely caused by outflow shocks in most cases, although shocks resulting from the cloud formation process could also play a role. Shock-origin for the HNCO, HC$_3$N, and CH$_3$CN emission is also plausible. The average HNC/HCN ratio is in good agreement with those seen in other IRDCs. Our results support the finding that C$_2$H can trace the cold gas, and not just the PDRs. The HC$_3$N/HCN ratio appears to be comparable to that in T Tauri disks and comets., Comment: 45 pages (incl. 3 appendices with 47 figures), 2 figures and 5 tables in the main text. Accepted for publication in A&A

We attempt to achieve a better understanding of the gas distribution and velocity field around the deeply embedded Class 0 protostar SMM 3 in the Orion B9 star-forming region. Using the APEX 12-m telescope, we mapped the line emission from the J=2-1 rotational transition of two CO isotopologues, 13CO and C18O, over a 4' x 4' region around Orion B9/SMM 3. Both the 13CO and C18O lines exhibit two well separated velocity components at about 1.3 and 8.7 km/s. The emission of both CO isotopologues is more widely distributed than the submillimetre dust continuum emission as probed by LABOCA. The LABOCA 870-micron peak position of SMM 3 is devoid of strong CO isotopologue emission, which is consistent with our earlier detection of strong CO depletion in the source. No signatures of a large-scale outflow were found towards SMM 3. The 13CO and C18O emission seen at ~1.3 km/s is concentrated into a single clump-like feature at the eastern part of the map. The peak H2 column density towards a C18O maximum of the low-velocity component is estimated to be ~10^22 cm-2. A velocity gradient was found across both the 13CO and C18O maps. Interestingly, SMM 3 lies on the border of this velocity gradient. The 13CO and C18O emission at ~1.3 km/s is likely to originate from the "low-velocity part" of Orion B. Our analysis suggests that it contains high density gas, which conforms to our earlier detection of deuterated species at similarly low radial velocities. The sharp velocity gradient in the region might represent a shock front resulting from the feedback from the nearby expanding HII region NGC 2024. The formation of SMM 3, and possibly of the other members of Orion B9, might have been triggered by this feedback., Comment: 11 pages, 9 figures, and 2 tables. Accepted for publication in Astronomy and Astrophysics

The aim of this study is to better understand the physical and chemical properties of the filamentary IRDC G304.74+01.32. In particular, we aim to investigate the kinematics and dynamical state of the cloud and clumps within it, and the amount of CO depletion. All the submillimetre peak positions in the cloud identified from our previous LABOCA 870-micron map were observed in C17O(2-1) with APEX. Selected positions were also observed in the 13CO(2-1), SiO(5-4), and CH3OH(5_k-4_k) transitions at ~1 mm wavelength. The C17O lines were detected towards all target positions at similar radial velocities, indicating that G304.74 is a coherent filamentary structure. CO does not appear to be significantly depleted in the clumps. Two- to three methanol 5_k-4_k lines near ~241.8 GHz were detected towards all selected target positions, whereas SiO(5-4) was seen in only one of these positions. The 13CO(2-1) lines show blue asymmetric profiles, indicating large-scale infall motions. The clumps show trans- to supersonic non-thermal motions, and virial-parameter analysis suggests that most of them are gravitationally bound. The external pressure may also play a non-negligible role in the dynamics. This is qualitatively consistent with our earlier suggestion that the filament was formed by converging supersonic turbulent flows. The analysis suggests that the fragmentation of the filament into clumps is caused by "sausage"-type instability, in agreement with results from other IRDCs. The star-formation activity in the cloud, such as outflows, is likely responsible in releasing CO from the icy grain mantles back into the gas phase. Shocks related to outflows may have also injected CH3OH, SiO, and DCN into the gas-phase in SMM 3., Comment: 17 pages, 9 figures, 7 tables, and 1 appendix. Accepted for publication in Astronomy & Astrophysics

We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The central part of Orion B9 was mapped at 350 micron with APEX/SABOCA. A sample of nine cores in the region were observed in C17O(2-1), H13CO+(4-3) (towards 3 sources), DCO+(4-3), N2H+(3-2), and N2D+(3-2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-micron dust continuum data. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image. In particular, we report on the discovery of multiple very low-mass condensations in the prestellar core SMM 6. Based on the 350-to-870 micron flux density ratios, we determine dust temperatures of ~7.9-10.8 K, and dust emissivity indices of ~0.5-1.8. The CO depletion factors are in the range ~1.6-10.8. The degree of deuteration in N2H+ is ~0.04-0.99, where the highest value (seen towards the prestellar core SMM 1) is, to our knowledge, the most extreme level of N2H+ deuteration reported so far. The level of HCO+ deuteration is about 1-2%. We also detected D2CO towards two sources. The detection of subcondensations within SMM 6 shows that core fragmentation can already take place during the prestellar phase. The origin of this substructure is likely caused by thermal Jeans fragmentation of the elongated parent core. A low depletion factor and the presence of gas-phase D2CO in SMM 1 suggest that the core chemistry is affected by the nearby outflow. The very high N2H+ deuteration in SMM 1 is likely to be remnant of the earlier CO-depleted phase., 20 pages, 10 figures, 10 tables. Accepted for publication in Astronomy and Astrophysics

Notwithstanding the importance of small software firms, research focusing on understanding the growth challenges faced by their management is close to non-existent. By taking a life-cycle approach and focusing on managerial challenges, the aim of this paper is to analyze the growth process of small software firms. After forming a synthesis of possible growth challenges from relevant literature, the results are reflected upon case software firms using thematic interviews and questionnaires. According to the analysis of four software firms, managing human resources represents the greatest challenge for software services firms. Additionally, other challenges stem from competition and sales-related activities. Comparative analysis of the literature and the cases leads toward a theoretical conceptualization of growth challenges from small software firm’s perspective.

We aim to determine the physical and chemical properties of dense cores in Orion B9. We observed the NH3(1,1) and (2,2), and the N2H+(3-2) lines towards the submm peak positions. These data are used in conjunction with our LABOCA 870 micron dust continuum data. The gas kinetic temperature in the cores is between ~9.4-13.9 K. The non-thermal velocity dispersion is subsonic in most of the cores. The non-thermal linewidth in protostellar cores appears to increase with increasing bolometric luminosity. The core masses are very likely drawn from the same parent distribution as the core masses in Orion B North. Starless cores in the region are likely to be gravitationally bound, and thus prestellar. Some of the cores have a lower radial velocity than the systemic velocity of the region, suggesting that they are members of the "low-velocity part" of Orion B. The observed core-separation distances deviate from the corresponding random-like model distributions. The distances between the nearest-neighbours are comparable to the thermal Jeans length. The fractional abundances of NH3 and N2H+ in the cores are ~1.5-9.8x10^{-8} and ~0.2-5.9x10^{-10}, respectively. The NH3 abundance appears to decrease with increasing H2 column and number densities. The NH3/N2H+ column density ratio is larger in starless cores than in cores with embedded protostars. The core population in Orion B9 is comparable in physical properties to those in nearby low-mass star-forming regions. It is unclear if the origin of cores could be explained by turbulent fragmentation. On the other hand, many of the core properties conform with the picture of dynamic core evolution. The Orion B9 region has probably been influenced by the feedback from the nearby Ori OB 1b group, and the fragmentation of the parental cloud into cores could be caused by gravitational instability., Comment: 17 pages, 11 figures, 7 tables. Accepted for publication in Astronomy and Astrophysics. Version 2: minor language corrections added

We present a 350 micron APEX/SABOCA map of IRAS 05399-0121/SMM 1, which is a dense double-core system in Orion B9. We combined these data with our previous LABOCA 870-micron data. The spatial resolution of the new SABOCA image, ~3400 AU, is about 2.6 times better than provided by LABOCA. We also make use of Spitzer infrared observations to characterise the star-formation activity in the source. The source is filamentary and remains a double-core system on the 3400 AU scale probed here, where the projected separation between IRAS 05399 and SMM 1 is 0.14 pc. The broadband spectral energy distribution of IRAS 05399 suggests that it is near the Stage 0/I borderline. A visual inspection of the Spitzer/IRAC images provides hints of a quadrupolar-like jet morphology around IRAS 05399, supporting the possibility that it is a binary system. The temperature map reveals warm spots towards IRAS 05399 and the southeastern tip of the source. These features are likely to be imprints of protostellar or shock heating, while external heating could be provided by the nearby high-mass star-forming region NGC 2024. A simple analysis suggests that the density profile at the position of SMM 1 has the form ~r^-(2.3_{-0.9}^{+2.2}). The source splitting into two subcores along the long axis can be explained by cylindrical Jeans-type fragmentation but the steepness of the density profile is shallower than what is expected for an isothermal cylinder. The difference between the evolutionary stages of IRAS 05399 (protostellar) and SMM 1 (starless) suggests that the former has experienced a phase of rapid mass accretion, supported by the very long outflow it drives. The protostellar jet from IRAS 05399 might have influenced the nearby core SMM 1., A&A, in press; 14 pages, 7 figures, 3 tables; very minor language corrections+revised arXiv abstract

The nearby protostellar core Cha-MMS1 has been mapped in the NH3 (1, 1) line and the 1.2 cm continuum using the Australia Telescope Compact Array, ATCA. In addition, observations from Spitzer Space Telescope and Herschel Space Observatory are used to help the interpretation. An elongated condensation with a maximum length of 9000 AU is seen in ammonia. The condensation has a clear velocity gradient directed perpendicularly to the axis of elongation. The gradient can be interpreted as rotation around this axis. We suggest that the observed ammonia structure delineates a rotating envelope and dense gas entrained by a very young protostellar outflow.

We have mapped four selected about 0.5 deg x 0.5 deg-sized fields containing Spitzer 8-micron dark regions with APEX/LABOCA at 870 micron. Selected positions in the fields were observed in C17O(2-1) to obtain kinematic information. The obtained LABOCA maps are used in conjunction with the Spitzer IR images. The total number of clumps identified in this survey is 91, out of which 40 (44%) appear dark at 8 and 24 micron. The remaining clumps are associated with mid-IR emission. Many of the identified clumps are massive enough to allow high-mass star formation, and some of them already show clear signposts of that. Seven clumps associated with extended-like 4.5 micron emission are candidate extended green objects (EGOs). Filamentary dust "ridges" were found towards the Spitzer bubbles N10/11 in one of our fields, which conforms to the triggered high-mass star formation in the system. The relative number of IR-dark and IR-bright clumps suggest that the duration of the former stage is about 1.6x10^5 yr. The mass distribution of the total sample of clumps, and that separately constructed for the IR-dark and IR-bright clumps, could be fitted at the high-mass end with the power-law function dN/dlogM ~ M^(-0.8...-0.7). The C17O observation positions appear to be dominated by non-thermal motions, and the data also revealed some potential sites of strong CO depletion. In G11.36+0.80, which is the best example of a filamentary IRDC in our sample, the clumps appear to be gravitationally bound. The fragmentation of the filament can be understood in terms of a "sausage"-type fluid instability, in agreement with the results for other IRDCs. The formation of filamentary IRDCs might be caused by converging turbulent flows, and the same process may play a role in exciting the fluid perturbations responsible for the fragmentation of the clouds into clumps., Comment: 23 pages, 14 figures, and 6 tables. Accepted for publication in Astronomy and Astrophysics

Infrared dark clouds (IRDCs) likely represent very early stages of high-mass star/star cluster formation. In this study, we aim to determine the physical properties and spatial distribution of dense clumps in the IRDC MSXDC G304.74+01.32 (G304.74), and bring these characteristics into relation to theories concerning the origin of IRDCs and their fragmentation into clumps and star-forming cores. G304.74 was mapped in the 870 $\mu$m dust continuum with the LABOCA bolometer on APEX. Archival MSX and IRAS infrared data were used to study the nature and properties of the submillimetre clumps within the cloud. There are 8 clumps within G304.74 which are not associated with mid-infrared (MIR) emission. Some of them are candidates for being/harbouring high-mass starless cores (HMSCs). We compared the clump masses and their spatial distribution in G304.74 with those in several other recently studied IRDCs. There is a high likelihood that the clump mass distributions in G304.74 and in several other IRDCs represent the samples of the same parent distribution. In most cases the spatial distributions of clumps in IRDCs do not deviate significantly from random distributions. This is consistent with the idea that the origin of IRDCs, and their further sub-fragmentation down to scales of clumps is caused by supersonic turbulence in accordance with results from giant molecular clouds., Comment: 15 pages, 8 figures, accepted for publication in Astronomy and Astrophysics