Suchergebnisse

Context. Long gamma-ray bursts (GRBs) can potentially be used as a tool to study star formation and recent gas accretion onto galaxies. However, the information about gas properties of GRB hosts is scarce. In particular, very few carbon monoxide (CO) line detections of individual GRB hosts have been reported. It has also been suggested that GRB hosts have lower molecular gas masses than expected from their star formation rates (SFRs). Aims. The objectives of this paper are to analyse molecular gas properties of the first substantial sample of GRB hosts and test whether they are deficient in molecular gas. Methods. We obtained CO(2-1) observations of seven GRB hosts with the APEX and IRAM 30 m telescopes. We analysed these data together with all other hosts with previous CO observations. From these observations we calculated the molecular gas masses of these galaxies and compared them with the expected values based on their SFRs and metallicities. Reults. We obtained detections for 3 GRB hosts (980425, 080207, and 111005A) and upper limits for the remaining 4 (031203, 060505, 060814, and 100316D). In our entire sample of 12 CO-observed GRB hosts, 3 are clearly deficient in molecular gas, even taking into account their metallicity (980425, 060814, and 080517). Four others are close to the best-fit line for other star-forming galaxies on the SFR-M2 plot (051022, 060505, 080207, and 100316D). One host is clearly molecule rich (111005A). Finally, the data for 4 GRB hosts are not deep enough to judge whether they are molecule deficient (000418, 030329, 031203, and 090423). The median value of the molecular gas depletion time, M2/SFR, of GRB hosts is ∼0.3 dex below that of other star-forming galaxies, but this result has low statistical significance. A Kolmogorov-Smirnov test performed on M2/SFR shows an only ∼2σ difference between GRB hosts and other galaxies. This difference can partly be explained by metallicity effects, since the significance decreases to ∼1σ for M2/SFR versus metallicity. Conclusions. We found that any molecular gas deficiency of GRB hosts has low statistical significance and that it can be attributed to their lower metallicities; and thus the sample of GRB hosts has molecular properties that are consistent with those of other galaxies, and they can be treated as representative star-forming galaxies. However, the molecular gas deficiency can be strong for GRB hosts if they exhibit higher excitations and/or a lower CO-To-H conversion factor than we assume, which would lead to lower molecular gas masses than we derive. Given the concentration of atomic gas recently found close to GRB and supernova sites, indicating recent gas inflow, our results about the weak molecular deficiency imply that such an inflow does not enhance the SFRs significantly, or that atomic gas converts efficiently into the molecular phase, which fuels star formation. Only if the analysis of a larger GRB host sample reveals molecular deficiency (especially close to the GRB position) would this support the hypothesis of star formation that is directly fuelled by atomic gas.© ESO 2018. ; M.J.M. acknowledges the support of the National Science Centre, Poland through the POLONEZ grant 2015/19/P/ST9/04010; and the UK Science and Technology Facilities Council; this project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 665778. A.K. acknowledges support from the Polish National Science Center grants 2014/15/B/ST9/02111and 2016/21/D/ST9/01098. J.R.R. acknowledges the support from project ESP2015-65597-C4-1-R (MINECO/FEDER). A.J.C.T. acknowledges support from the Spanish Ministry Project AYA2015-71718-R. J.H. was supported by a VILLUM FONDEN Investigator grant (project number 16599). L.K.H. acknowledges funding from the INAF PRIN-SKA program 1.05.01.88.04. M.R.K. acknowledges support from the Australian government through the Australian Research Council's Discovery Projects funding scheme (project DP160100695). ; Peer Reviewed

Aims: We compare the far-infrared to sub-millimetre dust emission properties measured in high Galactic latitude cirrus with those determined in a sample of 204 late-type DustPedia galaxies. The aim is to verify if it is appropriate to use Milky Way dust properties to derive dust masses in external galaxies. Methods: We used Herschel observations and atomic and molecular gas masses to estimate ∊(250 μm), the disc-averaged dust emissivity at 250 μm, and from this, the absorption cross section per H atom σ(250 μm) and per dust mass κ(250 μm). The emissivity ∊(250 μm) requires one assumption, which is the CO-to-H 2 conversion factor, and the dust temperature is additionally required for σ(250 μm); yet another constraint on the dust-to-hydrogen ratio D/H, depending on metallicity, is required for κ(250 μm). Results: We find ∊(250 μm) = 0.82 ± 0.07 MJy sr -1 (10 20 H cm -2 ) -1 for galaxies with 4 6, ∊(250 μm) is lower than predicted by its dependence on the heating conditions. The reduction suggests a variation in dust emission properties for spirals of earlier type, higher metallicity, and with a higher fraction of molecular gas. When the standard emission properties of Galactic cirrus are used for these galaxies, their dust masses might be underestimated by up to a factor of two. Values for σ(250 μm) and κ(250 μm) at the Milky Way metallicity are also close to those of the cirrus. Mild trends of the absorption cross sections with metallicity are found, although the results depend on the assumptions made. DustPedia is a collaborative focused research project supported by the European Union under the Seventh Framework Programme (2007-2013) call (proposal no. 606824, P.I. J. I. Davies, http://www.dustpedia.com ). The DustPedia data is publicly available at http://dustpedia.astro.noa.gr

Aims: We aim to study the fraction of stellar radiation absorbed by dust, f abs , in 814 galaxies of different morphological types. The targets constitute the vast majority (93%) of the DustPedia sample, including almost all large (optical diameter larger than 1'), nearby (v ≤ 3000 km s -1 ) galaxies observed with the Herschel Space Observatory. Methods: For each object, we modelled the spectral energy distribution from the ultraviolet to the sub-millimetre using the dedicated, aperture-matched DustPedia photometry and the Code Investigating GALaxy Evolution (CIGALE). The value of f abs was obtained from the total luminosity emitted by dust and from the bolometric luminosity, which are estimated by the fit. Results: On average, 19% of the stellar radiation is absorbed by dust in DustPedia galaxies. The fraction rises to 25% if only late-type galaxies are considered. The dependence of f abs on morphology, showing a peak for Sb-Sc galaxies, is weak; it reflects a stronger, yet broad, positive correlation with the bolometric luminosity, which is identified for late-type, disk-dominated, high-specific-star-formation rate, gas-rich objects. We find no variation of f abs with inclination, at odds with radiative transfer models of edge-on galaxies. These results call for a self-consistent modelling of the evolution of the dust mass and geometry along the build-up of the stellar content. We also provide template spectral energy distributions in bins of morphology and luminosity and study the variation of f abs with stellar mass and specific star-formation rate. We confirm that the local Universe is missing the high f abs , luminous and actively star-forming objects necessary to explain the energy budget in observations of the extragalactic background light. DustPedia is a collaborative focused research project supported by the European Union under the Seventh Framework Programme (2007-2013) call (proposal no. 606824, PI J. I. Davies, http://www.dustpedia.com ). The data used in this work is publicly available at ...