258 research outputs found
Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I.Observational Results
We present optical spectra and emission-line ratios of 12 Narrow-Line Seyfert
1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A
common feature in the EUV continuum of active galactic nuclei is the big blue
bump (BBB), generally associated with thermal accretion disk emission. While
Galactic absorption prevents direct access to the EUV range, it can be mapped
by measuring the strength of a variety of forbidden optical emission lines that
respond to different EUV continuum regions. We find that narrow emission-line
ratios involving [OII]3727, Hbeta, [OIII]5007, [OI]6300, Halpha,[NII]6583, and
[SII]6716,6731 indicate no significant difference between NLS1s and Broad-Line
Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy
distributions of their ionizing EUV - soft X-ray continua are similar. The
relative strength of important forbidden high ionization lines like [NeV]3426
compared to HeII4686 and the relative strength of [FeX]6374 appear to show the
same range as in BLS1 galaxies. However, a trend of weaker
F([OI]6300)/F(Halpha) emission-line ratios is indicated for NLS1s compared to
BLS1s. To recover the broad emission-line profiles we used Gaussian components.
This approach indicates that the broad Hbeta profile can be well described with
a broad component (FWHM = 3275 +- 800 km/s) and an intermediate broad component
(FWHM = 1200 +- 300 km/s). The width of the broad component is in the typical
range of normal BLS1s. The emission-line flux that is associated with the broad
component in these NLS1s amounts to at least 60% of the total flux. Thus it
dominates the total line flux, similar to BLS1 galaxies.Comment: 34 pages, 9 figures. accepted for publication in the
Astrophys.Journa
Subaru High-Dispersion Spectroscopy of Narrow-Line Region in the Seyfert Galaxy NGC 4151
We report on a study of forbidden emission-line spectrum of nearby Seyfert
1.5 galaxy NGC 4151 based on the high-resolution (R ~ 45,000) optical spectrum
obtained by using the High Dispersion Spectrograph boarded on the Subaru
Telescope. The profile parameters such as the emission-line widths, the
velocity shifts from the recession velocity of the host galaxy, and the
asymmetry indices, for emission lines including very faint ones such as [Ar
IV]4712,4740 and [Fe VI]5631,5677 are investigated. Statistically significant
correlations between the measured profile parameters and the critical densities
of transitions are found while there are no meaningful correlations between the
profile parameters and the ionization potentials of ions. By comparing the
results with photoionization model calculations, we remark that a simple
power-law distribution of the gas density which is independent of the radius
from the nucleus cannot explain the observed correlation between the
emission-line widths and the critical densities of the transitions. Taking the
additional dense gas component expected to exist at the innermost of the
narrow-line region into account, the observed correlations between the
emission-line width and the critical density of the transitions can be
understood since high-critical-density emission lines can arise at such
relatively inner regions even if their ionization potentials are low. The
observed correlation between the blueshift amounts of emission lines and the
critical densities of the ions is also explained if such dense gas clouds
located closer to the nucleus have larger outflowing velocities.Comment: 19 pages and 1 separate jpeg figure. Accepted for publication in A
A novel approach to study the morphology and chemistry of pollen in a phylogenetic context, applied to the halophytic taxon <em>Nitraria</em> L. (Nitrariaceae)
A novel approach to study the morphology and chemistry of pollen in a phylogenetic context, applied to the halophytic taxon <em>Nitraria</em> L. (Nitrariaceae)
On the nature of Seyfert galaxies with high [OIII]5007 blueshifts
We have studied the properties of Seyfert galaxies with high [OIII]5007
blueshifts (`blue outliers'), originally identified because of their strong
deviation from the M_BH - sigma relation of normal, narrow-line Seyfert 1
(NLS1) and broad-line Seyfert 1 (BLS1) galaxies. These blue outliers turn out
to be important test-beds for models of the narrow-line region (NLR), for
mechanisms of driving large-scale outflows, for links between NLS1 galaxies and
radio galaxies, and for orientation-dependent NLS1 models. We report the
detection of a strong correlation of line blueshift with ionization potential
in each galaxy, including the measurement of coronal lines with radial
velocities up to 500--1000 km/s. All [OIII] blue outliers have narrow widths of
their broad Balmer lines and high Eddington ratios. While the presence of
non-shifted low-ionization lines signifies the presence of a classical outer
quiescent NLR in blue outliers, we also report the absence of any second,
non-blueshifted [OIII] component from a classical inner NLR. These results
place tight constraints on NLR models. We favor a scenario in which the NLR
clouds are entrained in a decelerating wind which explains the strong
stratification and the absence of a zero-blueshift inner NLR of blue outliers.
The origin of the wind remains speculative at this time (collimated radio
plasma, thermal winds, radiatively accelerated clouds). It is perhaps linked to
the high Eddington ratios of blue outliers. Similar, less powerful winds could
be present in all Seyfert galaxies, but would generally only affect the coronal
line region (CLR), or level off even before reaching the CLR. Similarities
between blue outliers in NLS1 galaxies and (compact) radio sources are briefly
discussed.Comment: ApJ in press (scheduled for June 20 issue); incl. 4 colour figures.
This, and related paper showing that NLS1 galaxies follow the M-sigma
relation based on [SII], is also available at
http://www.xray.mpe.mpg.de/~skomossa
Chromosome-level reference genome of the soursop (Annona muricata): A new resource for Magnoliid research and tropical pomology
The flowering plant family Annonaceae includes important commercially grown tropical crops, but development of promising species is hindered by a lack of genomic resources to build breeding programs. Annonaceae are part of the magnoliids, an ancient lineage of angiosperms for which evolutionary relationships with other major clades remain unclear. To provide resources to breeders and evolutionary researchers, we report a chromosome‐level genome assembly of the soursop (Annona muricata). We assembled the genome using 444.32 Gb of DNA sequences (676× sequencing depth) from PacBio and Illumina short‐reads, in combination with 10× Genomics and Bionano data (v1). A total of 949 scaffolds were assembled to a final size of 656.77 Mb, with a scaffold N50 of 3.43 Mb (v1), and then further improved to seven pseudo‐chromosomes using Hi‐C sequencing data (v2; scaffold N50: 93.2 Mb, total size in chromosomes: 639.6 Mb). Heterozygosity was very low (0.06%), while repeat sequences accounted for 54.87% of the genome, and 23,375 protein‐coding genes with an average of 4.79 exons per gene were annotated using de novo, RNA‐seq and homology‐based approaches. Reconstruction of the historical population size showed a slow continuous contraction, probably related to Cenozoic climate changes. The soursop is the first genome assembled in Annonaceae, supporting further studies of floral evolution in magnoliids, providing an essential resource for delineating relationships of ancient angiosperm lineages. Both genome‐assisted improvement and conservation efforts will be strengthened by the availability of the soursop genome. As a community resource, this assembly will further strengthen the role of Annonaceae as model species for research on the ecology, evolution and domestication potential of tropical species in pomology and agroforestry
Infrared spectroscopy of NGC 1068: Probing the obscured ionizing AGN continuum
The ISO-SWS 2.5-45 um infrared spectroscopic observations of the nucleus of
the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a
compilation of UV to IR narrow emission line data to determine the spectral
energy distribution (SED) of the obscured extreme-UV continuum that
photoionizes the narrow line emitting gas in the active galactic nucleus. We
search a large grid of gas cloud models and SEDs for the combination that best
reproduces the observed line fluxes and NLR geometry. Our best fit model
reproduces the observed line fluxes to better than a factor of 2 on average and
is in general agreement with the observed NLR geometry. It has two gas
components that are consistent with a clumpy distribution of dense outflowing
gas in the center and a more extended distribution of less dense and more
clumpy gas farther out that has no net outflow. The best fit SED has a deep
trough at ~4 Ryd, which is consistent with an intrinsic Big Blue Bump that is
partially absorbed by ~6x10^19 cm^-2 of neutral hydrogen interior to the NLR.Comment: 15 pp, 4 figures, ApJ accepte
Outflows of very ionized gas in the center of Seyfert galaxies: kinematics and physical conditions
Mid-resolution spectra are used to deduce the size and kinematics of the
coronal gas in a sample of Seyfert galaxies by means of observations of the
[FeXI], [FeX], [FeVII], [SiVI] and [SiVII] lines. These coronal lines (CL)
extend from the unresolved nucleus up to a few tens to a few hundreds of
parsecs. The region of the highest ionized ions studied, [FeXI] and [FeX], is
the least spatially extended, and concentrates at the center; intermediate
ionization lines extend from the nucleus up to a few tens to a few hundred
parsecs; lower [OIII]-like ions are known to extendin the kpc range. All
together indicates a stratification in the ionized gas, usually interpreted in
terms of nuclear photoionization as the driving ionization mechanism. However,
CL profiles show various peculiarities: they are broader by a factor of two
than lower ionization lines, the broadening being in terms of asymmetric blue
wings, and their centroid position at the nucleus is blueshifted by a few
hundreds of km/s. Moreover, in NGC1386 and NGC1068, a double peak [FeVII] line
is detected in the nuclear and extended coronal region, this being the first
report in of such type of profile in CL in active galactic nuclei. If
interpreted as outflow signatures, the total broadening of the lines at zero
intensity levels implies gas velocities up to 2000 km/s. Although the
stratification of ions across the coronal region means that photoionization is
the main power mechanism, the high velocities deduced from the profiles, the
relatively large spatial extension of the emission, and the results from
photoionization models indicate that an additional mechanism is at work. We
suggest that shocks generated by the outflow could provide the additional
required power for line formation.Comment: Accepted for publication in the Astrophysical Journal. 40 pages, 15
figures. Minor changes made on the affiliation of one co-autho
Analyzing collaborative learning processes automatically
In this article we describe the emerging area of text classification research focused on the problem of collaborative learning process analysis both from a broad perspective and more specifically in terms of a publicly available tool set called TagHelper tools. Analyzing the variety of pedagogically valuable facets of learners’ interactions is a time consuming and effortful process. Improving automated analyses of such highly valued processes of collaborative learning by adapting and applying recent text classification technologies would make it a less arduous task to obtain insights from corpus data. This endeavor also holds the potential for enabling substantially improved on-line instruction both by providing teachers and facilitators with reports about the groups they are moderating and by triggering context sensitive collaborative learning support on an as-needed basis. In this article, we report on an interdisciplinary research project, which has been investigating the effectiveness of applying text classification technology to a large CSCL corpus that has been analyzed by human coders using a theory-based multidimensional coding scheme. We report promising results and include an in-depth discussion of important issues such as reliability, validity, and efficiency that should be considered when deciding on the appropriateness of adopting a new technology such as TagHelper tools. One major technical contribution of this work is a demonstration that an important piece of the work towards making text classification technology effective for this purpose is designing and building linguistic pattern detectors, otherwise known as features, that can be extracted reliably from texts and that have high predictive power for the categories of discourse actions that the CSCL community is interested in
Iron is not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei
In order to examine whether or not high-ionization nuclear emission-line
regions (HINERs) in narrow-line regions of active galactic nuclei are dusty, we
focus on two high-ionization forbidden emission lines, [Fe VII]6087 and [Ne
V]3426. We perform photoionization model calculations to investigate possible
dependences of the flux ratio of [Fe VII]6087/[Ne V]3426 on various gas
properties, in order to investigate how useful this flux ratio to explore the
dust abundances in HINERs. Based on our photoionization model calculations, we
show that the observed range of the flux ratio of [Fe VII]6087/[Ne V]3426 is
consistent with the dust-free models while that is hard to be explained by the
dusty models. This suggests that iron is not depleted at HINERs, which implies
that the HINERs are not dusty. This results is consistent with the idea that
the HINERs are located closer than the dust-sublimation radius (i.e., inner
radius of dusty tori) and thus can be hidden by dusty tori when seen from a
edge-on view toward the tori, which has been also suggested by the AGN-type
dependence of the visibility of high-ionization emission lines.Comment: 8 pages including 4 figures, to appear in The Astronomical Journa
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