The Global Structure and Evolution of a Self-Gravitating Multi-phase Interstellar Medium in a Galactic Disk

Using high resolution, two-dimensional hydrodynamical simulations, we investigate the evolution of a self-gravitating multi-phase interstellar medium in the central kiloparsec region of a galactic disk. We find that a gravitationally and thermally unstable disk evolves, in a self-stabilizing manner, into a globally quasi-stable disk that consists of cold (T < 100 K), dense clumps and filaments surrounded by hot (T > 10^4 K), diffuse medium. The quasi-stationary, filamentary structure of the cold gas is remarkable. The hot gas, characterized by low-density holes and voids, is produced by shock heating. The shocks derive their energy from differential rotation and gravitational perturbations due to the formation of cold dense clumps. In the quasi-stable phase where cold and dense clouds are formed, the effective stability parameter, Q, has a value in the range 2-5. The dynamic range of our multi-phase calculations is 10^6 - 10^7 in both density and temperature. Phase diagrams for this turbulent medium are analyzed and discussed.Comment: 10 pages, 3 figures, ApJ Letters in press (vol. 516

Star formation thresholds and galaxy edges: why and where

We study global star formation thresholds in the outer parts of galaxies by investigating the stability of disk galaxies embedded in dark halos. The disks are self-gravitating, contain metals and dust, and are exposed to UV radiation. We find that the critical surface density for the existence of a cold interstellar phase depends only weakly on the parameters of the model and coincides with the empirically derived surface density threshold for star formation. Furthermore, it is shown that the drop in the thermal velocity dispersion associated with the transition from the warm to the cold gas phase triggers gravitational instability on a wide range of scales. The presence of strong turbulence does not undermine this conclusion if the disk is self-gravitating. Models based on the hypothesis that the onset of thermal instability determines the star formation threshold in the outer parts of galaxies can reproduce many observations, including the threshold radii, column densities, and the sizes of stellar disks as a function of disk scale length and mass. Finally, prescriptions are given for implementing star formation thresholds in (semi-)analytic models and three-dimensional hydrodynamical simulations of galaxy formation.Comment: 16 pages, 6 figures, accepted for publication in the Astrophysical Journal. Version 2: text significantly revised (major improvements), physics unchanged. Version 3: minor correction

Galaxies on the Blue Edge

We have successfully constructed a catalog of HI-rich galaxies selected from the Minnesota Automated Plate Scanner Catalog of the Palomar Observatory Sky Survey (POSS I) based solely on optical criteria. We identify HI-rich candidates by selecting the bluest galaxies at a given apparent magnitude, those galaxies on the "blue edge" of POSS I color-magnitude parameter space. Subsequent 21-cm observations on the upgraded Arecibo 305m dish detected over 50% of the observed candidates. The detected galaxies are HI-rich with HI masses comparable to "normal" high surface brightness disk galaxies and they have gas mass-to-light ratios ranging from 0.1 to 4.8 (in solar units). Comparison of our candidate galaxies with known low surface brightness galaxies (hereafter LSBs) shows that they exhibit similar optical and HI properties to that population. We also show that previously identified LSBs, including several LSBs with red B-V colors, preferentially occupy the "blue edge" of POSS I color-magnitude parameter space. Their presence on the "blue edge" appears to be a selection effect due to differing plate limits in the two POSS I bandpasses. This suggests the POSS I is a good filter for separating galaxies on the higher surface brightness end of the LSB population from the general population of galaxies in the night sky.Comment: 56 pages, 19 figures, to be published in the Astronomical Journal (July 1, 2002

On the Neutral Gas Content and Environment of NGC 3109 and the Antlia Dwarf Galaxy

As part of a continuing survey of nearby galaxies, we have mapped the neutral gas content of the low surface brightness, Magellanic-type galaxy NGC 3109 --- and its environment, including the Antlia dwarf galaxy --- at unprecedented velocity resolution and brightness sensitivity. The HI mass of NGC 3109 is measured to be (3.8 +/- 0.5) x 10^8 Msun. A substantial warp in the disk of NGC 3109 is detected in the HI emission image in the form of an extended low surface brightness feature. We report a positive detection in HI of the nearby Antlia dwarf galaxy, and measure its total neutral gas mass to be (6.8 +/- 1.4) x 10^5 Msun. We show the warp in NGC 3109 to lie at exactly the same radial velocity as the gas in the Antlia dwarf galaxy and speculate that Antlia disturbed the disk of NGC 3109 during a mild encounter ~1 Gyr in the past. HI data for a further eight galaxies detected in the background are presented.Comment: Accepted for publication in A

CE19004

The 2019 Irish Anglerfish and Megrim Survey (IAMS) took place from 1-25th March (area 7bcjk) and 16-25th April 2019 (area 6a) on RV Celtic Explorer. The main objective of the survey is to obtain biomass and abundance indices for anglerfish (Lophius piscatorius and L. budegassa) and megrim (Lepidorhombus whiffiagonis and L. boscii) in areas 6a (south of 58°N) and 7 (west of 8°W). Secondary objectives are to collect data on the distribution, relative abundance and biology of other commercially exploited species. This year, additional sampling took place in deep water (up to 1,500m) in order to monitor the recovery of exploited deep-water species following the decline of the deep-water fisheries in Irish waters. The IAMS survey is coordinated with the Scottish Anglerfish and Megrim Survey (SIAMISS) and uses the same gear and fishing practices

Spectroscopy of Low Surface Brightness Galaxies with the Hobby-Eberly Telescope

We have obtained low resolution spectra of nineteen red and blue low surface brightness galaxies, using the Marcario Low Resolution Spectrograph on the 9.2m Hobby-Eberly Telescope. These galaxies form a very heterogeneous class, whose spectra qualitatively resemble those of high surface brightness galaxies covering the full range of spectra seen in galaxies of Hubble types from E to Irr. We use a combination of emission line (EW(Halpha), NII/Halpha) and absorption line (Mgb, Hbeta, ) based diagnostics to investigate the star-formation and chemical enrichment histories of these galaxies. These are diverse, with some galaxies having low metallicity and very young mean stellar ages, and other galaxies showing old, super-solar metallicity stellar populations. In contrast with some previous studies which found a strong trend of decreasing metallicity with decreasing central surface brightness, we find a population of galaxies with low surface brightness and near-solar metallicity. Correlations between several of the gas phase and stellar population age and metallicity indicators are used to place contraints on plausible evolutionary scenarios for LSB galaxies. The redshift range spanned by these galaxies is broad, with radial velocities from 3400 km/s to more than 65000 km/s. A subset of the sample galaxies have published HI redshifts and gas masses based on observations with the Arecibo 305m single-dish radio telescope, which place these galaxies far off of the mean Tully-Fisher relation. Our new optical redshifts do not agree with the published HI redshifts for these galaxies. Most of the discrepancies can be explained by beam confusion in the Arecibo observations, causing erroneous HI detections for some of the galaxies.Comment: 31 pages, 12 figures, 7 tables. Uses emulateapj5.sty and onecolfloat5.sty, which are included. Accepted for publication in the Astronomical Journa

Tooth loss and oral health-related quality of life: a systematic review and meta-analysis

Contains fulltext : 87677.pdf (publisher's version ) (Open Access)BACKGROUND: It is increasingly recognized that the impact of disease on quality of life should be taken into account when assessing health status. It is likely that tooth loss, in most cases being a consequence of oral diseases, affects Oral Health-Related Quality of Life (OHRQoL). The aim of the present study is to systematically review the literature and to analyse the relationship between the number and location of missing teeth and oral health-related quality of life (OHRQoL). It was hypothesized that tooth loss is associated with an impairment of OHRQoL. Secondly, it was hypothesized that location and distribution of remaining teeth play an important role in this. METHODS: Relevant databases were searched for papers in English, published from 1990 to July 2009 following a broad search strategy. Relevant papers were selected by two independent readers using predefined exclusion criteria, firstly on the basis of abstracts, secondly by assessing full-text papers. Selected studies were grouped on the basis of OHRQoL instruments used and assessed for feasibility for quantitative synthesis. Comparable outcomes were subjected to meta-analysis; remaining outcomes were subjected to a qualitative synthesis only. RESULTS: From a total of 924 references, 35 were eligible for synthesis (inter-reader agreement abstracts kappa = 0.84 +/- 0.03; full-texts: kappa = 0.68 +/- 0.06). Meta-analysis was feasible for 10 studies reporting on 13 different samples, resulting in 6 separate analyses. All studies showed that tooth loss is associated with unfavourable OHRQoL scores, independent of study location and OHRQoL instrument used. Qualitative synthesis showed that all 9 studies investigating a possible relationship between number of occluding pairs of teeth present and OHRQoL reported significant positive correlations. Five studies presented separate data regarding OHRQoL and location of tooth loss (anterior tooth loss vs. posterior tooth loss). Four of these reported highest impact for anterior tooth loss; one study indicated a similar impact for both locations of tooth loss. CONCLUSIONS: This study provides fairly strong evidence that tooth loss is associated with impairment of OHRQoL and location and distribution of tooth loss affect the severity of the impairment. This association seems to be independent from the OHRQoL instrument used and context of the included samples

The Baryonic Tully-Fisher Relation

We explore the Tully-Fisher relation over five decades in stellar mass in galaxies with circular velocities ranging over 30 < Vc < 300 km/s. We find a clear break in the optical Tully-Fisher relation: field galaxies with Vc < 90 km/s fall below the relation defined by brighter galaxies. These faint galaxies are however very gas rich; adding in the gas mass and plotting baryonic disk mass Md = M* + Mg in place of luminosity restores a single linear relation. The Tully-Fisher relation thus appears fundamentally to be a relation between rotation velocity and total baryonic mass of the form Md = A Vc^4.Comment: 10 pages including 1 color figure. Accepted for publication in ApJ Letter

Star Formation from Galaxies to Globules

The empirical laws of star formation suggest that galactic-scale gravity is involved, but they do not identify the actual triggering mechanisms for clusters in the final stages. Many other triggering processes satisfy the empirical laws too, including turbulence compression and expanding shell collapse. The self-similar nature of the gas and associated young stars suggests that turbulence is more directly involved, but the small scale morphology of gas around most embedded clusters does not look like a random turbulent flow. Most clusters look triggered by other nearby stars. Such a prominent local influence makes it difficult to understand the universality of the Kennicutt and Schmidt laws on galactic scales. A unified view of multi-scale star formation avoids most of these problems. Ambient self-gravity produces spiral arms and drives much of the turbulence that leads to self-similar structures, while localized energy input from existing clusters and field supernovae triggers new clusters in pre-existing clouds. The hierarchical structure in the gas made by turbulence ensures that the triggering time scales with size, giving the Schmidt law over a wide range of scales and the size-duration correlation for young star fields. The efficiency of star formation is determined by the fraction of the gas above a critical density of around 10^5 m(H2)/cc. Star formation is saturated to its largest possible value given the fractal nature of the interstellar medium.Comment: accepted for ApJ, 42 pages, Dannie Heineman prize lecture, January 200