Diffuse neutral hydrogen in the HI Parkes All Sky Survey

Observations of neutral hydrogen can provide a wealth of information about the distribution and kinematics of galaxies. To detect HI beyond the ionisation edge of galaxy disks, column density sensitivities have to be achieved that probe the regime of Lyman limit systems. Typically HI observations are limited to a brightness sensitivity of NHI~10^19 cm-2 but this has to be improved by at least an order of magnitude. In this paper, reprocessed data is presented that was originally observed for the HI Parkes All Sky Survey (HIPASS). HIPASS provides complete coverage of the region that has been observed for the Westerbork Virgo Filament HI Survey (WVFS), presented in accompanying papers, and thus is an excellent product for data comparison. The region of interest extends from 8 to 17 hours in right ascension and from -1 to 10 degrees in declination. Although the original HIPASS product already has good flux sensitivity, the sensitivity and noise characteristics can be significantly improved with a different processing method. The newly processed data has an 1sigma RMS flux sensitivity of ~10 mJy beam-1 over 26 km s-1, corresponding to a column density sensitivity of ~3\cdot10^17 cm-2. While the RMS sensitivity is improved by only a modest 20%, the more substantial benefit is in the reduction of spectral artefacts near bright sources by more than an order of magnitude. In the reprocessed region we confirm all previously catalogued HIPASS sources and have identified 29 additional sources of which 14 are completely new HI detections. Extended emission or companions were sought in the nearby environment of each discrete detection. With the improved sensitivity after reprocessing and its large sky coverage, the HIPASS data is a valuable resource for detection of faint HI emission.(Abridged)Comment: 22 pages plus appendix, 6 figures, appendix will only appear in online format. Accepted for publication in A&

The ESO UVES Advanced Data Products Quasar Sample - I. Dataset and New N_HI Measurements of Damped Absorbers

We present here a dataset of quasars observed with the Ultraviolet Visual Echelle Spectrograph (UVES) on the VLT and available in the ESO UVES Advanced Data Products archive. The sample is made up of a total of 250 high resolution quasar spectra with emission redshifts ranging from 0.191 < z_em <6.311. The total UVES exposure time of this dataset is 1560 hours. Thanks to the high resolution of UVES spectra, it is possible to unambiguously measure the column density of absorbers with damping wings, down to N_HI > 10^{19} cm^{-2}, which constitutes the sub-damped Lya absorber (sub-DLA) threshold. Within the wavelength coverage of our UVES data, we find 150 damped Lya systems (DLAs)/sub-DLAs in the range 1.5 < z_abs < 4.7. Of these 150, 93 are DLAs and 57 are sub-DLAs. An extensive search in the literature indicates that 6 of these DLAs and 13 of these sub-DLAs have their N_HI measured for the first time. Among them, 10 are new identifications as DLAs/sub-DLAs. For each of these systems, we obtain an accurate measurement of the HI column density and the absorber's redshift in the range 1.7 < z_abs < 4.2 by implementing a Voigt profile-fitting algorithm. These absorbers are further confirmed thanks to the detection of associated metal lines and/or lines from members of the Lyman series. In our data, a few quasars' lines-of-sight are rich. An interesting example is towards QSO J0133+0400 (z_em = 4.154) with six DLAs and sub-DLAs reported.Comment: 16 pages, 24 figures, 3 table

Dissecting the IRX - β\beta dust attenuation relation: exploring the physical origin of observed variations in galaxies

The use of ultraviolet (UV) emission as a tracer of galaxy star-formation rate (SFR) is hampered by dust obscuration. The empirical relationship between UV slope, $\beta$, and the ratio between far-infrared and UV luminosity, IRX, is commonly employed to account for obscured UV emission. We present a simple model that explores the physical origin of variations in the IRX - $\beta$ dust attenuation relation. A relative increase in FUV attenuation compared to NUV attenuation and an increasing stellar population age cause variations towards red UV slopes for a fixed IRX. Dust geometry effects (turbulence, dust screen with holes, mixing of stars within the dust screen, two-component dust model) cause variations towards blue UV slopes. Poor photometric sampling of the UV spectrum causes additional observational variations. We provide an analytic approximation for the IRX - $\beta$ relation invoking a subset of the explored physical processes (dust type, stellar population age, turbulence). We discuss observed variations in the IRX - $\beta$ relation for local (sub-galactic scales) and high-redshift (normal and dusty star-forming galaxies, galaxies during the epoch of reionization) galaxies in the context of the physical processes explored in our model. High spatial resolution imaging of the UV and sub-mm emission of galaxies can constrain the IRX - $\beta$ dust attenuation relation for different galaxy types at different epochs, where different processes causing variations may dominate. These constraints will allow the use of the IRX - $\beta$ relation to estimate intrinsic SFRs of galaxies, despite the lack of a universal relation.Comment: Accepted for publication in MNRA

Evolution of the atomic and molecular gas content of galaxies in dark matter haloes

We present a semi-empirical model to infer the atomic and molecular hydrogen content of galaxies as a function of halo mass and time. Our model combines the SFR-halo mass-redshift relation (constrained by galaxy abundances) with inverted SFR-surface density relations to infer galaxy H I and H2 masses. We present gas scaling relations, gas fractions, and mass functions from z = 0 to z = 3 and the gas properties of galaxies as a function of their host halo masses. Predictions of our work include: 1) there is a ~ 0.2 dex decrease in the H I mass of galaxies as a function of their stellar mass since z = 1.5, whereas the H2 mass of galaxies decreases by > 1 dex over the same period. 2) galaxy cold gas fractions and H2 fractions decrease with increasing stellar mass and time. Galaxies with M* > 10^10 Msun are dominated by their stellar content at z < 1, whereas less-massive galaxies only reach these gas fractions at z = 0. We find the strongest evolution in relative gas content at z < 1.5. 3) the SFR to gas mass ratio decreases by an order of magnitude from z = 3 to z = 0. This is consistent with lower H2 fractions; these lower fractions in combination with smaller gas reservoirs correspond to decreased present-day galaxy SFRs. 4) an H2-based star- formation relation can simultaneously fuel the evolution of the cosmic star-formation and reproduce the observed weak evolution in the cosmic HI density. 5) galaxies residing in haloes with masses near 10^12 Msun are most efficient at obtaining large gas reservoirs and forming H2 at all redshifts. These two effects lie at the origin of the high star-formation efficiencies in haloes with the same mass.Comment: accepted for publication in MNRAS, 20 pages, 16 figures (+ 1 figure in appendix), data files are accessible through http://www.eso.org/~gpopping/Gergo_Poppings_Homepage/Data.htm

Knowledge Graphs and Network Text Analysis

A knowledge graph is a kind of semantic network representing some scientific theory. The article describes the present state of this field and addresses a number of problems that have not yet been solved. These problems are implicit relations, strength of (causal) relations, and exclusiveness. Concepts might be too broad or complex to be used properly, so directions for solving these problems are explored. The solutions are applied to a knowledge graph in the field of labour markets

A Scheme for the Study of Discussions in the Social Media

In case one wants to study discussions in the social media one needs a template for doing this. The discussions can range from comments on some event to developing a deliberative democracy. This template, or scoring system, should give insight in developments in the substance of the discussion, but it should also allow considering the development of the structure of the discussion. In this text a template is proposed that covers both questions. The information that is collected by using the template might be useful in the context of (new) policy making; it can also be used to study opinions