185 research outputs found
Across the Digital Divide: A Cross-Country Multi-Technology Analysis of the Determinants of IT Penetration
This paper studies the country-level digital divide across successive generations of IT, providing detailed insights into the magnitude and changing nature of the divide. We examine a panel of 40 countries from 1985-2001, based on data from three distinct generations of IT: mainframes, personal computers, and the Internet. Using two measures of IT penetration, we conduct an empirical investigation of socio-economic factors driving the digital divide. We find that IT penetration is positively associated with national income for all three technology generations, and the association between penetration and income is stronger for countries with higher levels of IT penetration. We also examine other demographic and economic factors, going beyond income, and find significant differences in the nature of their effects across countries at different stages of IT adoption. Importantly, factors that previously may have been expanding the divide with earlier technologies are narrowing the gap as the Internet becomes the defining technology of the Information Age
Feeding versus Feedback in NGC 4151 probed with Gemini NIFS. I. Excitation
We have used the Gemini Near-infrared Integral Field Spectrograph (NIFS) to
map the emission-line intensity distributions and ratios in the Narrow-Line
Region (NLR) of the Seyfert galaxy NGC 4151 in the Z, J, H and K bands at a
resolving power ~ 5000, covering the inner 200 pc x 300 pc of the galaxy at a
spatial resolution of 8 pc. We present intensity distributions I(r) in 14
emission lines. (1) For the ionized gas, I(r) is extended to ~ 100 pc from the
nucleus along pos. angle PA=60/240 deg-- NE--SW), consistent with an origin in
the known biconical outflow; while for the recombination lines I(r) ~ r^-1, for
the forbidden lines I(r) is flat (r^0). (2) The H_2 emission lines intensity
distributions avoid the region of the bicone, extending to r ~ 60 pc,
perpendicular to the bicone axis, supporting an origin for the H_2-emitting gas
in the galaxy plane. (3) The coronal lines show a steep intensity profile,
described by r^-2. Using the line-ratio maps [Fe II]1.644/1.257 and Pa_b/Br_g
we obtain a reddening of E(B-V)~0.5 along the NLR and E(B-V)>1 at the nucleus.
Our line-ratio map [Fe II] 1.257/[P II] 1.189 is the first such map of an
extragalactic source. Together with the [Fe II]/Pa_b map, these line ratios
correlate with the radio intensity distribution, mapping the effects of shocks
produced by the radio jet, which probably release the Fe locked in grains and
produce the enhancement of the [Fe II] emission observed at ~ 1 arcsec from the
nucleus. At these regions, we obtain densities N_e ~4000 cm^-3 and temperatures
T_e ~ 15000K for the [Fe II]-emitting gas. For the H_2-emitting gas we obtain T
~ 2100K. The distinct intensity distributions, physical properties and
locations of the ionized and molecular gas suggest that the H_2-emitting gas
traces the AGN feeding, while the ionized gas traces its feedback.Comment: 22 pages. 14 figures, accepted for publication in MNRA
Discovery of Highly Obscured Galaxies in the Zone of Avoidance
We report the discovery of twenty-five previously unknown galaxies in the
Zone of Avoidance. Our systematic search for extended extra-galactic sources in
the GLIMPSE and MIPSGAL mid-infrared surveys of the Galactic plane has revealed
two overdensities of these sources, located around l ~ 47 and 55 degrees and
|b| less than 1 degree in the Sagitta-Aquila region. These overdensities are
consistent with the local large-scale structure found at similar Galactic
longitude and extending from |b| ~ 4 to 40 degrees. We show that the infrared
spectral energy distribution of these sources is indeed consistent with those
of normal galaxies. Photometric estimates of their redshift indicate that the
majority of these galaxies are found in the redshift range z = 0.01 - 0.05,
with one source located at z = 0.07. Comparison with known sources in the local
Universe reveals that these galaxies are located at similar overdensities in
redshift space. These new galaxies are the first evidence of a bridge linking
the large-scale structure between both sides of the Galactic plane at very low
Galactic latitude and clearly demonstrate the feasibility of detecting galaxies
in the Zone of Avoidance using mid-to-far infrared surveys.Comment: Accepted for publication in the Astronomical Journal, 28 pages, 5
tables, 11 figure
Enhancing access to the Bibliome: the TREC 2004 Genomics Track
BACKGROUND: The goal of the TREC Genomics Track is to improve information retrieval in the area of genomics by creating test collections that will allow researchers to improve and better understand failures of their systems. The 2004 track included an ad hoc retrieval task, simulating use of a search engine to obtain documents about biomedical topics. This paper describes the Genomics Track of the Text Retrieval Conference (TREC) 2004, a forum for evaluation of IR research systems, where retrieval in the genomics domain has recently begun to be assessed. RESULTS: A total of 27 research groups submitted 47 different runs. The most effective runs, as measured by the primary evaluation measure of mean average precision (MAP), used a combination of domain-specific and general techniques. The best MAP obtained by any run was 0.4075. Techniques that expanded queries with gene name lists as well as words from related articles had the best efficacy. However, many runs performed more poorly than a simple baseline run, indicating that careful selection of system features is essential. CONCLUSION: Various approaches to ad hoc retrieval provide a diversity of efficacy. The TREC Genomics Track and its test collection resources provide tools that allow improvement in information retrieval systems
Near-IR dust and line emission from the central region of Mrk1066: Constraints from Gemini NIFS
We present integral field spectroscopy of the inner 350 pc of the Mrk1066
obtained with Gemini NIFS at a spatial resolution of 35 pc. This high spatial
resolution allowed us to observe, for the first time in this galaxy, an
unresolved dust concentration with mass 0.014 M_Sun, which may be part of the
dusty torus. The emission-line fluxes are elongated in PA=135/315deg in
agreement with the [OIII] and radio images and, except for the H lines, are
brighter to the north-west than to the south-east. The H emission is stronger
to the south-east, where we find a large region of star-formation. The strong
correlation between the radio emission and the highest emission-line fluxes
indicates that the radio jet plays a fundamental role at these intensity
levels. The H2 flux is more uniformly distributed and has an excitation
temperature of 2100 K. Its origin appears to be circumnuclear gas heated by
X-rays from the AGN. The [FeII] emission also is consistent with X-ray heating,
but with additional emission due to excitation by shocks in the radio jet. The
coronal-line emission of [CaVIII] and [SIX] are unresolved by our observations
indicating a distribution within 18pc from the nucleus. The reddening ranges
from E(B-V) ~ 0 to E(B-V) ~ 1.7 with the highest values defining a S-shaped
structure along PA ~ 135/315deg. The emission-line ratios are Seyfert-like
within the ionization cone indicating that the line emission is powered by the
central active nucleus in these locations. Low ionization regions are observed
away from the ionization cone, and may be powered by the diffuse radiation
field which filters through the ionization cone walls. Two regions at 0.5
arcsec south-east and at 1 arcsec north-west of the nucleus show starburst-like
line ratios, attributed to additional emission from star forming regions.Comment: 14 pages, 10 figures, accepted for publication in MNRA
SMA/PdBI multiple line observations of the nearby Seyfert2 galaxy NGC 1068: Shock related gas kinematics and heating in the central 100pc?
We present high angular resolution (0.5-2.0") observations of the mm
continuum and the 12CO(J=3-2), 13CO(J=3-2), 13CO(J=2-1), C18O(J=2-1),
HCN(J=3-2), HCO+(J=4-3) and HCO+(J=3-2) line emission in the circumnuclear disk
(r=100pc) of the proto-typical Seyfert type-2 galaxy NGC1068, carried out with
the Submillimeter Array. We further include in our analysis new 13CO(J=1-0) and
improved 12CO(J=2-1) observations of NGC1068 at high angular resolution
(1.0-2.0") and sensitivity, conducted with the IRAM Plateau de Bure
Interferometer. Based on the complex dynamics of the molecular gas emission
indicating non-circular motions in the central ~100pc, we propose a scenario in
which part of the molecular gas in the circumnuclear disk of NGC1068 is
radially blown outwards as a result of shocks. This shock scenario is further
supported by quite warm (Tkin>=200K) and dense (nH2=10^4cm^-3) gas constrained
from the observed molecular line ratios. The HCN abundance in the circumnuclear
disk is found to be [HCN]/[12CO]=10^-3.5. This is slightly higher than the
abundances derived for galactic and extragalactic starforming/starbursting
regions. This results lends further support to X-ray enhanced HCN formation in
the circumnuclear disk of NGC1068, as suggested by earlier studies. The HCO+
abundance ([HCO+]/[12CO]=10^-5) appears to be somewhat lower than that of
galactic and extragalactic starforming/starbursting regions. When trying to fit
the cm to mm continuum emission by different thermal and non-thermal processes,
it appears that electron-scattered synchrotron emission yields the best results
while thermal free-free emission seems to over-predict the mm continuum
emission.Comment: accepted for publication by ApJ; 35pages, 22 figures and 6 tables (at
the end of the file); 3 figures have been decreased in quality to match size
limi
SCG0018-4854: a young and dynamic compact group I. Kinematical analysis
Compact groups of galaxies are in particular good laboratories for studying
galaxy interactions and their effects on the evolution of galaxies due to their
high density and low velocity dispersion. SCG0018-4854 is a remarkably high
galaxy density and low velocity dispersion group with evidence of a recent
interaction. We obtained VLT FORS2 optical observations and we present
spectroscopic and photometric evidence of how dramatically galaxy interactions
have affected each of the four member galaxies. We found peculiar kinematics
for each galaxy and evidence of recent star formation. In particular, the gas
and stellar radial velocity curves of two galaxies are irregular with a level
of asymmetry similar to that of other interacting galaxies. We discovered the
presence of a bar for NGC 92 therefore revising a previous morphological
classification and we obtained spectroscopic confirmation of a galactic-scale
outflow of NGC 89. Peculiar kinematics and dynamic consideration lead to a
rough estimate of the age of the latest interaction: 0.2-0.7 Gyr, suggesting
that SCG0018-4854 is a young and dynamical group.Comment: 11 pages, 12 figures, to be published in A&
Unusual PAH Emission in Nearby Early-Type Galaxies: A Signature of an Intermediate Age Stellar Population?
We present the analysis of Spitzer-IRS spectra of four early-type galaxies,
NGC 1297, NGC 5044, NGC 6868, and NGC 7079, all classified as LINERs in the
optical bands. Their IRS spectra present the full series of H2 rotational
emission lines in the range 5--38 microns, atomic lines, and prominent PAH
features. We investigate the nature and origin of the PAH emission,
characterized by unusually low 6 -- 9/11.3 microns inter-band ratios. After the
subtraction of a passive early type galaxy template, we find that the 7 -- 9
microns spectral region requires dust features not normally present in star
forming galaxies. Each spectrum is then analyzed with the aim of identifying
their components and origin. In contrast to normal star forming galaxies, where
cationic PAH emission prevails, our 6--14 microns spectra seem to be dominated
by large and neutral PAH emission, responsible for the low 6 -- 9/11.3 microns
ratios, plus two broad dust emission features peaking at 8.2 microns and 12
microns. Theses broad components, observed until now mainly in evolved carbon
stars and usually attributed to pristine material, contribute approximately
30-50% of the total PAH flux in the 6--14 microns region. We propose that the
PAH molecules in our ETGs arise from fresh carbonaceous material which is
continuously released by a population of carbon stars, formed in a rejuvenation
episode which occurred within the last few Gyr. The analysis of the MIR spectra
allows us to infer that, in order to maintain the peculiar size and charge
distributions biased to large and neutral PAHs, this material must be shocked,
and excited by the weak UV interstellar radiation field of our ETG.Comment: ApJ accepte
The Mid-Infrared High-Ionization Lines from Active Galactic Nuclei and Star-Forming Galaxies
We used Spitzer/IRS spectroscopic data on 426 galaxies including quasars,
Seyferts, LINER and HII galaxies to investigate the relationship among the
mid-IR emission lines. There is a tight linear correlation between the [Ne
V]14.3 um and 24.3 um (97.1 eV) and the [O IV]25.9 um (54.9 eV) high-ionization
emission lines. The correlation also holds for these high-ionization emission
lines and the [Ne III]15.56 um (41 eV) emission line, although only for active
galaxies. We used these correlations to calculate the [Ne III] excess due to
star formation in Seyfert galaxies. We also estimated the [O IV] luminosity due
to star formation in active galaxies and determined that it dominates the [O
IV] emission only if the contribution of the active nucleus to the total
luminosity is below 5%. We find that the AGN dominates the [O IV] emission in
most Seyfert galaxies, whereas star-formation adequately explains the observed
[O IV] emission in optically classified HII galaxies. Finally we computed
photoionization models to determine the physical conditions of the narrow line
region where these high-ionization lines originate. The estimated ionization
parameter range is -2.8 < log U < -2.5 and the total hydrogen column density
range is 20 < log nH (cm-2) < 21.Comment: Accepted for Publication in ApJ, 19 pages, 13 figure
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