13,533 research outputs found
Retrieval information file relating to assigned frequencies, part 2 Final report, Jan. - Sep. 1969
Retrieval information file relating to assigned frequencies for use on IBM 360 compute
Millimetre/submillimetre-wave emission line searches for high-redshift galaxies
The redshifted spectral line radiation emitted from both atomic
fine-structure and molecular rotational transitions in the interstellar medium
(ISM) of high-redshift galaxies can be detected in the centimetre, millimetre
and submillimetre wavebands. Here we predict the counts of galaxies detectable
in an array of molecular and atomic lines. This calculation requires a
reasonable knowledge of both the surface density of these galaxies on the sky,
and the physical conditions in their ISM. The surface density is constrained
using the results of submillimetre-wave continuum surveys. Follow-up OVRO
Millimeter Array observations of two of the galaxies detected in the dust
continuum have provided direct measurements of CO rotational line emission at
redshifts of 2.56 and 2.81. Based on these direct high-redshift observations
and on models of the ISM that are constrained by observations of low-redshift
ultraluminous infrared galaxies, we predict the surface density of
line-emitting galaxies as a function of line flux density and observing
frequency. We incorporate the sensitivities and mapping speeds of existing and
future millimetre/submillimetre-wave telescopes and spectrographs, and so
assess the prospects for blank-field surveys to detect this line emission from
gas-rich high-redshift galaxies.Comment: 13 pages, 12 figures, to appear in MNRAS. Final proof versio
The Translational Apparatus of Plastids and Its Role in Plant Development
Chloroplasts (plastids) possess a genome and their own machinery to express it. Translation in plastids occurs on bacterial-type 70S ribosomes utilizing a set of tRNAs that is entirely encoded in the plastid genome. In recent years, the components of the chloroplast translational apparatus have been intensely studied by proteomic approaches and by reverse genetics in the model systems tobacco (plastid-encoded components) and Arabidopsis (nucleus-encoded components). This work has provided important new insights into the structure, function, and biogenesis of chloroplast ribosomes, and also has shed fresh light on the molecular mechanisms of the translation process in plastids. In addition, mutants affected in plastid translation have yielded strong genetic evidence for chloroplast genes and gene products influencing plant development at various levels, presumably via retrograde signaling pathway(s). In this review, we describe recent progress with the functional analysis of components of the chloroplast translational machinery and discuss the currently available evidence that supports a significant impact of plastid translational activity on plant anatomy and morphology
{LOLA}: enrichment analysis for genomic region sets and regulatory elements in {R} and {Bioconductor}
Radial distribution of gas and dust in spiral galaxies: The case of Mâ99 (NGCâ4254) and Mâ100 (NGCâ4321)
By combining Herschel-SPIRE data with archival Spitzer, Hâiâ, and CO maps, we investigate the spatial distribution of gas and dust in the two famous grand-design spirals Mâ99 and Mâ100 in the Virgo cluster. Thanks to the unique resolution and sensitivity of the Herschel-SPIRE photometer, we are for the first time able to measure the distribution and extent of cool, submillimetre (submm)-emitting dust inside and beyond the optical radius. We compare this with the radial variation in both the gas mass and the metallicity. Although we adopt a model-independent, phenomenological approach, our analysis provides important insights. We find the dust extending to at least the optical radius of the galaxy and showing breaks in its radial profiles at similar positions as the stellar distribution. The colour indices f350/f500 and f250/f350 decrease radially consistent with the temperature decreasing with radius. We also find evidence of an increasing gas to dust ratio with radius in the outer regions of both galaxies
SPIRE imaging of Mâ82: Cool dust in the wind and tidal streams
Mâ82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the Mâ81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind
Herschel photometric observations of the low metallicity dwarf galaxy NGC 1705
We present Herschel SPIRE and PACS photometeric observations of the low metallicity (Z ~ 0.35 Z_â) nearby dwarf galaxy, NGC 1705, in six wavelength bands as part of the Dwarf Galaxy Survey guaranteed time Herschel key program. We confirm the presence of two dominant circumnuclear IR-bright regions surrounding the central super star cluster that had been previously noted at mid-IR wavelengths and in the sub-mm by LABOCA. On constructing a global spectral energy distribution using the SPIRE and PACS photometry, in conjunction with archival IR measurements, we note the presence of an excess at sub-mm wavelengths. This excess suggests the presence of a significant cold dust component within NGC 1705 and was modeled as an additional cold component in the SED. Although alternative explanations for the sub-mm excess beyond 350 ÎŒm, such as changes to the dust emissivity cannot be ruled out, the most likely explanation for the observed submillimetre excess is that of an additional cold dust component
The central region of spiral galaxies as seen by Herschel: M 81, M 99, and M 100
With appropriate spatial resolution, images of spiral galaxies in thermal infrared (~10 ÎŒm and beyond) often reveal a bright central component, distinct from the stellar bulge, superimposed on a disk with prominent spiral arms. ISO and Spitzer studies have shown that much of the scatter in the mid-infrared colors of spiral galaxies is related to changes in the relative importance of these two components, rather than to other modifications, such as the morphological type or star formation rate, that affect the properties of the galaxy as a whole. With the Herschel imaging capability from 70 to 500 ÎŒm, we revisit this two-component approach at longer wavelengths, to see if it still provides a working description of the brightness
distribution of galaxies, and to determine its implications on the interpretation of global far-infrared properties of galaxies. We quantify the luminosity of the central component by both a decomposition of the radial surface brightness profile and a direct extraction in 2D.
We find the central component contribution is variable within the three galaxies in our sample, possibly connected more directly to the presence of a bar than to the morphological type. The central componentâs relative contribution is at its maximum in the mid-infrared range and drops around 160 ÎŒm to reach a constant value beyond 200 ÎŒm. The central component contains a greater fraction of hot dust than the disk component, and while the colors of the central components are scattered, colors of the disk components are more homogenous from one galaxy to the next
The Herschel Space Observatory view of dust in M81
We use Herschel Space Observatory data to place observational constraints on the peak and Rayleigh-Jeans slope of dust emission observed at 70â500 ÎŒm in the nearby spiral galaxy M81. We find that the ratios of wave bands between 160 and 500 ÎŒm are primarily dependent on radius but that the ratio of 70 to 160 ÎŒm emission shows no clear dependence on surface brightness or radius. These
results along with analyses of the spectral energy distributions imply that the 160â500 ÎŒm emission traces 15â30 K dust heated by evolved stars in the bulge and disc whereas the 70 ÎŒm emission includes dust heated by the active galactic nucleus and young stars in star forming regions
The dust morphology of the elliptical Galaxy M86 with SPIRE
We present Herschel-SPIRE observations at 250â500âÎŒm of the giant elliptical galaxy Mâ86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10âkpc to the south-east. We estimate that ~10^6âM_â of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC 4438 due to recent tidal interactions with Mâ86. The gas-to-dust ratio of the cold gas component ranges from ~20â80. We discuss the different heating mechanisms for the dust features
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