913 research outputs found
The Host Galaxies of Narrow-Line Seyfert 1s: Evidence for Bar-Driven Fueling
We present a study of the host-galaxy morphologies of narrow- and broad-line
Seyfert 1 galaxies (NLS1s and BLS1s) based on broad-band optical images from
the Hubble Space Telescope archives. We find that large-scale stellar bars,
starting at ~1 kpc from the nucleus, are much more common in NLS1s than BLS1s.
Furthermore, the fraction of NLS1 spirals that have bars increases with
decreasing full-width at half-maximum (FWHM) of the broad component of H-beta.
These results suggest a link between the large-scale bars, which can support
high fueling rates to the inner kpc, and the high mass-accretion rates
associated with the supermassive black holes in NLS1s.Comment: 19 pages, 4 figures (1a, 1b, 2, and 3), Accepted for publication in
the Astronomical Journa
Raman and fluorescence contributions to resonant inelastic soft x-ray scattering on LaAlO/SrTiO heterostructures
We present a detailed study of the Ti 3 carriers at the interface of
LaAlO/SrTiO heterostructures by high-resolution resonant inelastic soft
x-ray scattering (RIXS), with special focus on the roles of overlayer thickness
and oxygen vacancies. Our measurements show the existence of interfacial Ti
3 electrons already below the critical thickness for conductivity and an
increase of the total interface charge up to a LaAlO overlayer thickness of
6 unit cells before it levels out. By comparing stoichiometric and oxygen
deficient samples we observe strong Ti 3 charge carrier doping by oxygen
vacancies. The RIXS data combined with photoelectron spectroscopy and transport
measurements indicate the simultaneous presence of localized and itinerant
charge carriers. However, it is demonstrated that the relative amount of
localized and itinerant Ti electrons in the ground state cannot be deduced
from the relative intensities of the Raman and fluorescence peaks in excitation
energy dependent RIXS measurements, in contrast to previous interpretations.
Rather, we attribute the observation of either the Raman or the fluorescence
signal to the spatial extension of the intermediate state reached in the RIXS
excitation process.Comment: 9 pages, 6 figure
Jet emission in NGC1052 at radio, optical, and X-ray frequencies
We present a combined radio, optical, and X-ray study of the nearby LINER
galaxy NGC 1052. Data from a short (2.3 ksec) {\it CHANDRA} observation of NGC
1052 reveal the presence of various jet-related X-ray emitting regions, a
bright compact core and unresolved knots in the jet structure as well as an
extended emitting region inside the galaxy well aligned with the radio
synchrotron jet-emission. The spectrum of the extended X-ray emission can best
be fitted with a thermal model with keV, while the compact
core exhibits a very flat spectrum, best approximated by an absorbed power-law
with . We compare the radio
structure to an optical ``structure map'' from a {\it Hubble Space Telescope}
({\it HST}) observation and find a good positional correlation between the
radio jet and the optical emission cone. Bright, compact knots in the jet
structure are visible in all three frequency bands whose spectrum is
inconsistent with synchrotron emission.Comment: 8 pages, 5 figures (figure 2 in color), image resolution degraded wrt
journal version, needs aa.cls. Accepted for publication in A&
The Narrow-Line Regions of LINERs as Resolved with the Hubble Space Telescope
LINERs exist in the nuclei of a large fraction of luminous galaxies, but
their connection with the AGN phenomenon has remained elusive. We present
Hubble Space Telescope narrowband [O III]5007 and H-alpha+[N II] emission-line
images of the central regions of 14 galaxies with LINER nuclei. The compact, ~1
arcsec-scale, unresolved emission that dominates the line flux in ground-based
observations is mostly resolved by HST. The bulk of this emission comes from
regions with sizes of tens to hundreds of parsecs that are resolved into knots,
filaments, and diffuse gas whose morphology differs from galaxy to galaxy. Most
of the galaxies do not show clear linear structures or ionization cones
analogous to those often seen in Seyfert galaxies. An exception is NGC 1052,
the prototypical LINER, in which we find a 3 arcsec-long (~ 250 pc) biconical
structure that is oriented on the sky along the galaxy's radio jet axis. Seven
of the galaxies have been shown in previously published HST images to have a
bright compact ultraviolet nuclear source, while the other seven do not have a
central UV source. Our images find evidence of dust in the nuclear regions of
all 14 galaxies, with clear indications of nuclear obscuration in most of the
"UV-dark" cases. The data suggest that the line-emitting gas in most LINERs is
photoionized by a central source (which may be stellar, nonstellar, or a
combination thereof) but that this source is often hidden from direct view. We
find no obvious morphological differences between LINERs with detected weak
broad H-alpha wings in their spectra and those with only narrow lines.
Likewise, there is no clear morphological distinction between objects whose UV
spectra are dominated by hot stars (e.g., NGC 4569) and those that are AGN-like
(e.g., NGC 4579).Comment: Accepted for publication in the ApJ. 25 pages, 3 tables, 9 JPEG
Figure
Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. II. Physical Conditions in the UV Absorbers
We present a detailed analysis of the intrinsic absorption in the Seyfert 1
galaxy NGC 4151 using UV spectra from the HST/STIS and FUSE, obtained 2002 May
as part of a set of contemporaneous observations that included Chandra/HETGS
spectra. In our analysis of the Chandra spectra, we determined that the soft
X-ray absorber was the source of the saturated UV lines of O VI, C IV, and N V
associated with the absorption feature at a radial velocity of ~ -500 km/sec,
which we referred to as component D+E. In the present work, we have derived
tighter constrains on the the line-of-sight covering factors, densities, and
radial distances of the absorbers. We find that the Equivalent Widths (EWs) of
the low-ionization lines associated with D+E varied over the period from 1999
July to 2002 May. The drop in the EWs of these lines between 2001 April and
2002 May are suggestive of bulk motion of gas out of our line-of-sight. If
these lines from these two epochs arose in the same sub-component, the
transverse velocity of the gas is ~ 2100 km/sec. Transverse velocities of this
order are consistent with an origin in a rotating disk, at the roughly radial
distance we derived for D+E.Comment: 51 pages, including 12 figures. Accepted for publication in ApJ
Supplement
A Real-Time Ball Detection Approach Using Convolutional Neural Networks
Ball detection is one of the most important tasks in the context of soccer-playing robots. The ball is a small moving object which can be blurred and occluded in many situations. Several neural network based methods with different architectures are proposed to deal with the ball detection. However, they are either neglecting to consider the computationally low resources of humanoid robots or highly depend on manually-tuned heuristic methods to extract the ball candidates. In this paper, we propose a new ball detection method for low-cost humanoid robots that can detect most soccer balls with a high accuracy rate of up to 97.17%. The proposed method is divided into two steps. First, some coarse regions that may contain a full ball are extracted using an iterative method employing an efficient integral image based feature. Then they are fed to a light-weight convolutional neural network to finalize the bounding box of a ball. We have evaluated the proposed approach using a comprehensive dataset and the experimental results show the efficiency of our method
Variable UV Absorption in the Seyfert 1.5 Galaxy NGC 3516: The Case for Associated UV and X-ray Absorption
We present observations of the UV absorption lines in the Seyfert 1 galaxy
NGC 3516, obtained at a resolution of /
40,000 with the Space Telescope Imaging Spectrograph (STIS) on 2000 October 1.
The UV continuum was 4 times lower than that observed during 1995 with
the Goddard High Resolution Spectrograph (GHRS), and the X-ray flux from a
contemporaneous {\it Chandra X-ray Observatory (CXO)} observation was a factor
of 8 below that observed with {\it ASCA}. The STIS spectra show kinematic
components of absorption in Ly, C IV, and N V at radial velocities of
-376, -183, and -36 km s (components 1, 2, and 3+4, respectively), which
were detected in the earlier GHRS spectra; the last of these is a blend of two
GHRS components that have increased greatly in column density. Four additional
absorption components have appeared in the STIS spectra at radial velocities of
-692, -837, -994, and -1372 km s (components 5 through 8); these may
also have been present in earlier low-flux states observed by the {\it
International Ultraviolet Explorer (IUE)}. Based on photoionization models, we
suggest that the components are arranged in increasing radial distance in the
order, 3+4, 2, 1, followed by components 5 -- 8. We have achieved an acceptable
fit to the X-ray data using the combined X-ray opacity of the UV components 1,
2 and 3+4. By increasing the UV and X-ray fluxes of these models to match the
previous high states, we are able to match the GHRS C IV column densities,
absence of detectable C IV absorption in components 5 through 8, and the 1994
{\it ASCA} spectrum. We conclude that variability of the UV and X-ray
absorption in NGC 3516 is primarily due to changes in the ionizing flux.Comment: 7 figures (note that Fig6 is not referenced in the .Tex file and must
be printed separately). There are 6 tables in the .tex file and an additional
8 tables included as separate .ps files. Accepted for Publication in the
Astrophysical Journa
The Ionized Gas and Nuclear Environment in NGC 3783 V. Variability and Modeling of the Intrinsic Ultraviolet Absorption
We present results on the location, physical conditions, and geometry of the
outflow in the Seyfert 1 galaxy NGC 3783 from a study of the variable intrinsic
UV absorption. Based on 18 observations with HST/STIS and 6 observations with
FUSE, we find: 1) The absorption from the lowest-ionization species in each of
the three strong kinematic components varied inversely with the continuum flux,
indicating the ionization structure responded to changes in the photoionizing
flux over the weekly timescales sampled by our observations. 2) A multi-
component model with an unocculted NLR and separate BLR and continuum
line-of-sight covering factors predicts saturation in several lines, consistent
with the lack of observed variability. 3) Column densities for the individual
metastable levels are measured from the resolved C III *1175 absorption complex
observed in one component. Based on our computed metastable level populations,
the electron density of this absorber is ~3x10^4 cm^-3. Photoionization
modeling results place it at ~25 pc from the central source. 4) Using
time-dependent calculations, we are able to reproduce the detailed variability
observed in this absorber, and derive upper limits on the distances for the
other components of 25-50 pc. 5) The ionization parameters derived for the
higher ionization UV absorbers are consistent with the modeling results for the
lowest-ionization X-ray component, but with smaller total column density. They
have similar pressures as the three X-ray ionization components. These results
are consistent with an inhomogeneous wind model for the outflow in NGC 3783. 6)
Based on the predicted emission-line luminosities, global covering factor
constraints, and distances derived for the UV absorbers, they may be identified
with emission- line gas observed in the inner NLR of AGNs. (abridged)Comment: 30 pages, 18 figures (7 color), emulateapj, accepted for publication
in The Astrophysical Journa
LONGO: An R package for interactive gene length dependent analysis for neuronal identity
Motivation: Reprogramming somatic cells into neurons holds great promise to model neuronal development and disease. The efficiency and success rate of neuronal reprogramming, however, may vary between different conversion platforms and cell types, thereby necessitating an unbiased, systematic approach to estimate neuronal identity of converted cells. Recent studies have demonstrated that long genes (\u3e100 kb from transcription start to end) are highly enriched in neurons, which provides an opportunity to identify neurons based on the expression of these long genes.
Results: We have developed a versatile R package, LONGO, to analyze gene expression based on gene length. We propose a systematic analysis of long gene expression (LGE) with a metric termed the long gene quotient (LQ) that quantifies LGE in RNA-seq or microarray data to validate neuronal identity at the single-cell and population levels. This unique feature of neurons provides an opportunity to utilize measurements of LGE in transcriptome data to quickly and easily distinguish neurons from non-neuronal cells. By combining this conceptual advancement and statistical tool in a user-friendly and interactive software package, we intend to encourage and simplify further investigation into LGE, particularly as it applies to validating and improving neuronal differentiation and reprogramming methodologies.
Availability and implementation: LONGO is freely available for download at https://github.com/biohpc/longo.
Supplementary information: Supplementary data are available at Bioinformatics online
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