26,233 research outputs found
Searching for additional heating - [OII] emission in the diffuse ionized gas of NGC891, NGC4631 and NGC3079
We present spectroscopic data of ionized gas in the disk--halo regions of
three edge-on galaxies, NGC 891, NGC 4631 and NGC 3079, covering a wavelength
range from [\ion{O}{2}] 3727\AA to [\ion{S}{2}] 6716.4\AA.
The inclusion of the [\ion{O}{2}] emission provides new constraints on the
properties of the diffuse ionized gas (DIG), in particular, the origin of the
observed spatial variations in the line intensity ratios. We used three
different methods to derive electron temperatures, abundances and ionization
fractions along the slit. The increase in the [\ion{O}{2}]/H line ratio
towards the halo in all three galaxies requires an increase either in electron
temperature or in oxygen abundance. Keeping the oxygen abundance constant
yields the most reasonable results for temperature, abundances, and ionization
fractions. Since a constant oxygen abundance seems to require an increase in
temperature towards the halo, we conclude that gradients in the electron
temperature play a significant role in the observed variations in the optical
line ratios from extraplanar DIG in these three spiral galaxies.Comment: 43 pages, 29 figure
Boundary crossing Random Walks, clinical trials and multinomial sequential estimation
A sufficient condition for the uniqueness of multinomial sequential unbiased
estimators is provided generalizing a classical result for binomial samples.
Unbiased estimators are applied to infer the parameters of multidimensional or
multinomial Random Walks which are observed until they reach a boundary. An
application to clinical trials is presented
The use of remote sensing in solving Florida's geological and coastal engineering problems
LANDSAT imagery and NASA high altitude color infrared (CIR) photography were used to select suitable sites for sanitary landfill in Volusia County, Florida and to develop techniques for preventing sand deposits in the Clearwater inlet. Activities described include the acquisition of imagery, its analysis by the IMAGE 100 system, conventional photointerpretation, evaluation of existing data sources (vegetation, soil, and ground water maps), site investigations for ground truth, and preparation of displays for reports
Relationships between skin follicle characteristics and fibre properties of Suri and Huacaya alpacas and Peppin Merino sheep
We aimed to quantify the number, type and arrangement of skin follicles in Huacaya and Suri alpaca skin and correlate their follicle characteristics with fibre traits of harvested fibre and compared these relationships with those of Merino sheep. Fibre and skin samples were collected from the mid-side of 12 Huacaya alpacas, 24 Suri alpacas and 10 Merino sheep. The mean fibre diameter (MFD ± s.e.) of the Huacaya and Suri were: 35.5 ± 0.9 and 28.3 ± 1.0 μm, respectively. The follicle groups found for alpacas were very different from the normal trio of primary follicles found in sheep and goats. The follicle group of the alpacas consisted of a single primary follicle surrounded by a variable number of secondary follicles. The mean ± s.e. primary follicle density was 3.1 ± 0.3 and 2.7 ± 0.1 follicles/mm2 for Huacaya and Suri, respectively. The mean ± s.e. secondary follicle density (SFD) was 13.7 ± 1.2 and 17.5 ± 0.6 follicles/mm2 for Huacaya and Suri, respectively. The mean ± s.e. ratio of secondary to primary follicles (S/P ratio) was 5.1 ± 0.5 for the Huacaya and 7.3 ± 0.2 for the Suri alpacas. The sheep had higher S/P ratios and SFD, lower MFD and produced significantly heavier fleeces. The key correlations found between traits in alpacas include a negative correlation between SFD and MFD (r = –0.71, P = 0.001) and a negative correlation between S/P ratio and MFD (r = –0.44, P = 0.003) and a positive correlation between S/P ratio and total follicle density (r = 0.38, P = 0.010). The study revealed that important relationships exist between alpaca skin follicle characteristics and fibre characteristics. It was the number of secondary follicles in a group that imparts density and a corresponding reduced MFD.<br /
The NextGen Model Atmosphere grid: II. Spherically symmetric model atmospheres for giant stars with effective temperatures between 3000 and 6800~K
We present the extension of our NextGen model atmosphere grid to the regime
of giant stars. The input physics of the models presented here is nearly
identical to the NextGen dwarf atmosphere models, however spherical geometry is
used self-consistently in the model calculations (including the radiative
transfer). We re-visit the discussion of the effects of spherical geometry on
the structure of the atmospheres and the emitted spectra and discuss the
results of NLTE calculations for a few selected models.Comment: ApJ, in press (November 1999), 13 pages, also available at
http://dilbert.physast.uga.edu/~yeti/PAPERS and at
ftp://calvin.physast.uga.edu/pub/preprints/NG-giants.ps.g
Deep UV Luminosity Functions at the Infall Region of the Coma Cluster
We have used deep GALEX observations at the infall region of the Coma cluster
to measure the faintest UV luminosity functions (LFs) presented for a rich
galaxy cluster thus far. The Coma UV LFs are measured to M_UV = -10.5 in the
GALEX FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach
the dwarf early-type galaxy population in Coma for the first time. The
Schechter faint-end slopes (alpha = -1.39 in both GALEX bands) are shallower
than reported in previous Coma UV LF studies owing to a flatter LF at faint
magnitudes. A Gaussian-plus-Schechter model provides a slightly better
parametrization of the UV LFs resulting in a faint-end slope of ~ -1.15 in both
GALEX bands. The two-component model gives faint-end slopes shallower than -1
(a turnover) for the LFs constructed separately for passive and star forming
galaxies. The UV LFs for star forming galaxies show a turnover at M_UV ~ -14
owing to a deficit of dwarf star forming galaxies in Coma with stellar masses
below M*=10^8 Msun. A similar turnover is identified in recent UV LFs measured
for the Virgo cluster suggesting this may be a common feature of local galaxy
clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did
not identify an excess of passive galaxies as would be expected if the missing
dwarf star forming galaxies were quenched inside the cluster. In fact, the LFs
for both dwarf passive and star forming galaxies show the same turnover at
faint magnitudes. We discuss the possible origin of the missing dwarf star
forming galaxies in Coma and their expected properties based on comparisons to
local field galaxies.Comment: accepted for publication in Ap
The AGN Outflow in the HDFS Target QSO J2233-606 from a High-Resolution VLT/UVES Spectrum
We present a detailed analysis of the intrinsic UV absorption in the central
HDFS target QSO J2233-606, based on a high-resolution, high S/N (~25 -- 50)
spectrum obtained with VLT/UVES. This spectrum samples the cluster of intrinsic
absorption systems outflowing from the AGN at radial velocities v ~ -5000 --
-3800 km/s in the key far-UV diagnostic lines - the lithium-like CNO doublets
and H I Lyman series. We fit the absorption troughs using a global model of all
detected lines to solve for the independent velocity-dependent covering factors
of the continuum and emission-line sources and ionic column densities. This
reveals increasing covering factors in components with greater outflow
velocity. Narrow substructure is revealed in the optical depth profiles,
suggesting the relatively broad absorption is comprised of a series of multiple
components. We perform velocity-dependent photoionization modeling, which
allows a full solution to the C, N, and O abundances, as well as the velocity
resolved ionization parameter and total column density. The absorbers are found
to have supersolar abundances, with [C/H] and [O/H] ~0.5 -- 0.9, and [N/H] ~
1.1 -- 1.3, consistent with enhanced nitrogen production expected from
secondary nucleosynthesis processes. Independent fits to each kinematic
component give consistent results for the abundances. The lowest-ionization
material in each of the strong absorbers is modeled with similar ionization
parameters. Components of higher-ionization (indicated by stronger O VI
relative to C IV and N V) are present at velocities just redward of each
low-ionization absorber. We explore the implications of these results for the
kinematic-geometric-ionization structure of the outflow.Comment: 12 pages, 10 figures, emulateapj, accepted for publication in Ap
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