WHAM Observations of H-alpha from High-Velocity Clouds: Are They Galactic or Extragalactic?

It has been suggested that high velocity clouds may be distributed throughout the Local Group and are therefore not in general associated with the Milky Way galaxy. With the aim of testing this hypothesis, we have made observations in the H-alpha line of high velocity clouds selected as the most likely candidates for being at larger than average distances. We have found H-alpha emission from 4 out of 5 of the observed clouds, suggesting that the clouds under study are being illuminated by a Lyman continuum flux greater than that of the metagalactic ionizing radiation. Therefore, it appears likely that these clouds are in the Galactic halo and not distributed throughout the Local Group.Comment: 12 pages, 5 eps figures, accepted for publication in ApJ Letter

Theoretical He I Emissivities in the Case B Approximation

We calculate the He I case B recombination cascade spectrum using improved radiative and collisional data. We present new emissivities over a range of electron temperatures and densities. The differences between our results and the current standard are large enough to have a significant effect not only on the interpretation of observed spectra of a wide variety of objects but also on determinations of the primordial helium abundance.Comment: Accepted to ApJ

A New Observational Upper Limit to the Low Redshift Ionizing Background Radiation

We report a new Fabry-Perot search for Halpha emission from the intergalactic cloud HI 1225+01 in an attempt to measure the low redshift ionizing background radiation. We set a new 2 sigma upper limit on Halpha emission of 8 mR (5 x 10^{-20} ergs cm^{-2} s^{-1} arcsec^{-2}). Conversion of this limit to limits on the strength of the ionizing background requires knowledge of the ratio of the projected to total surface area of this cloud, which is uncertain. We discuss the plausible range of this ratio, and within this range find that the strength of the ionizing backround is in the lower range of, but consistent with, previous observational and theoretical estimates.Comment: 46 pages including 9 figures (7 ps, 2 gif

Improving Predictions for Helium Emission Lines

We have combined the detailed He I recombination model of Smits with the collisional transitions of Sawey & Berrington in order to produce new accurate helium emissivities that include the effects of collisional excitation from both the 2 (3)S and 2 (1) S levels. We present a grid of emissivities for a range of temperature and densities along with analytical fits and error estimates. Fits accurate to within 1% are given for the emissivities of the brightest lines over a restricted range for estimates of primordial helium abundance. We characterize the analysis uncertainties associated with uncertainties in temperature, density, fitting functions, and input atomic data. We estimate that atomic data uncertainties alone may limit abundance estimates to an accuracy of 1.5%; systematic errors may be greater than this. This analysis uncertainty must be incorporated when attempting to make high accuracy estimates of the helium abundance. For example, in recent determinations of the primordial helium abundance, uncertainties in the input atomic data have been neglected.Comment: ApJ, accepte

Accurate Hydrogen Spectral Simulations with a Compact Model Atom

Many large scale numerical simulations of astrophysical plasmas must also reproduce the hydrogen ionization and the resulting emission spectrum, in some cases quite accurately. We describe a compact model hydrogen atom that can be readily incorporated into such simulations. It reproduces the recombination efficiency and line spectrum predicted by much larger calculations for a very broad range of densities and temperatures. Uncertainties in hydrogen collision data are the largest source of differences between our compact atom and predictions of more extensive calculations, and underscore the need for accurate atomic data.Comment: 18 pages, prepared in MS-Word, Postscript only, 12 Figures, also available at http://www.pa.uky.edu/~ferguson/bib/bib.html, accepted for publication in the Astrophysical Journa

Selection of Forages for the Tropics (SoFT) - A Database and Selection Tool for Identifying Forages Adapted to Local Conditions in the Tropics and Subtropics

Rising populations and incomes in developing countries are likely to double demand for livestock products by 2020 (Delgado et al. 1999). This strong demand has potential to improve profitability for farmers but will require improved animal feeding in both semi-intensive crop-livestock and more extensive livestock systems. Forages usually are the most cost-effective option to supply feed demands, particularly for ruminant-, but also for pig- and poultry- production. It is critical to select the most suitable forages for the local system and conditions. Small- and even larger-scale farmers depend heavily on advice from extension and development agencies, and from seed companies, but this advice often is limited by inexperience and the difficulty in accessing reliable information. Expert information on an extensive range of tropical forages is now readily available through the SoFT database

Deleterious coding variants in multi-case families with non-syndromic cleft lip and/or palate phenotypes

8 páginasNonsyndromic Cleft Lip and/or Palate (NSCLP) is regarded as a multifactorial condition in which clefting is an isolated phenotype, distinguished from the largely monogenic, syndromic forms which include clefts among a spectrum of phenotypes. Nonsyndromic clefting has been shown to arise through complex interactions between genetic and environmental factors. However, there is increasing evidence that the broad NSCLP classification may include a proportion of cases showing familial patterns of inheritance and contain highly penetrant deleterious variation in specific genes. Through exome sequencing of multi-case families ascertained in Bogota, Colombia, we identify 28 non-synonymous single nucleotide variants that are considered damaging by at least one predictive score. We discuss the functional impact of candidate variants identified. In one family we find a coding variant in the MSX1 gene which is predicted damaging by multiple scores. This variant is in exon 2, a highly conserved region of the gene. Previous sequencing has suggested that mutations in MSX1 may account for ~2% of NSCLP. Our analysis further supports evidence that a proportion of NSCLP cases arise through monogenic coding mutations, though further work is required to unravel the complex interplay of genetics and environment involved in facial clefting

Dust and molecules in the Local Group galaxy NGC 6822. III. The first-ranked HII region complex Hubble V

We present maps of the first-ranked HII region complex Hubble V in the metal-poor Local Group dwarf galaxy NGC 6822 in the first four transitions of CO, the 158 micron transition of C+, the 21-cm line of HI, the Pa-beta line of HII, and the continuum at 21 cm and 2.2 micron wavelengths. We have also determined various integrated intensities, notably of HCO+ and near-IR H2 emission. Although Hubble X is located in a region of relatively strong HI emission, our mapping failed to reveal any significant CO emission from it. The relatively small CO cloud complex associated with Hubble V is comparable in size to the ionized HII region. The CO clouds are hot (Tkin) = 150 K) and have high molecular gas densities (n(H2) = 10**4 cm**-3) Molecular hydrogen probably extends well beyond the CO boundaries. C+ column densities are more than an order of magnitude higher than those of CO. The total mass of the complex is about 10**6 M(sun) and molecular gas account for more than half of this. The complex is excited by luminous stars reddened or obscured at visual, but apparent at near-infrared wavelengths. The total embedded stellar mass may account for about 10% of the total mass, and the mass of ionized gas for half of that. Hubble V illustrates that modest star formation efficiencies may be associated with high CO destruction efficiencies in low-metallicity objects. The analysis of the Hubble V photon-dominated region (PDR) confirms in an independent manner the high value of the CO-to-H2 conversion factor X found earlier, characteristic of starforming low-metallicity regions.Comment: Accepted for publication in A&

Towards a free-free template for CMB foregrounds

A full-sky template map of the Galactic free-free foreground emission component is increasingly important for high sensitivity CMB experiments. We use the recently published \ha data of both the northern and southern skies as the basis for such a template. The first step is to correct the \ha maps for dust absorption using the 100 $\mu$m dust maps of Schlegel, Finkbeiner & Davis (1998). We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected \ha map can be produced for $\sim 95$ per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area $|b| < 5^{\circ}$, $l=260^{\circ}-0^{\circ}-160^{\circ}$ and some isolated dense dust clouds at intermediate latitudes. The second step is to convert the dust-corrected \ha data into a predicted radio surface brightness. The free-free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz to 100 GHz and the electron temperature range 3000 to 20000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H{\sc ii} regions using data in the range 408 to 2326 MHz. A full-sky free-free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408 MHz map of the sky can be corrected for this free-free component, which amounts to a $\approx 6$ per cent correction at intermediate and high latitudes....Comment: 18 pages, 11 figures, accepted for publication in M.N.R.A.S. High-resolution versions of figs 2,7 (in colour), 9 and 11 can be obtained from ftp://ftp.jb.man.ac.uk/pub/cdickins/ff_paper/FINAL_FIGURES