5,623 research outputs found
CLASS Survey Description: Coronal Line Needles in the SDSS Haystack
Coronal lines are a powerful, yet poorly understood, tool to identify and
characterize Active Galactic Nuclei (AGNs). There have been few large scale
surveys of coronal lines in the general galaxy population in the literature so
far. Using a novel pre-selection technique with a flux-to-RMS ratio ,
followed by Markov-Chain Monte Carlo (MCMC) fitting, we searched for the full
suite of 20 coronal lines in the optical spectra of almost 1 million galaxies
from the Sloan Digital Sky Survey (SDSS) Data Release 8. We present a catalog
of the emission line parameters for the resulting 258 galaxies with detections.
The Coronal Line Activity Spectroscopic Survey (CLASS) includes line
properties, host galaxy properties, and selection criteria for all galaxies in
which at least one line is detected. This comprehensive study reveals that a
significant fraction of coronal line activity is missed in past surveys based
on a more limited set of coronal lines; 60% of our sample do not display
the more widely surveyed [Fe X] 6374. In addition, we discover a
strong correlation between coronal line and WISE W2 luminosities, suggesting
that the mid-infrared flux can be used to predict coronal line fluxes. For each
line we also provide a confidence level that the line is present, generated by
a novel neural network, trained on fully simulated data. We find that after
training the network to detect individual lines using 100,000 simulated
spectra, we achieve an overall true positive rate of 75.49% and a false
positive rate of only 3.96%.Comment: 27 pages, 16 figures, 4 table
Towards a global understanding of the drivers of marine and terrestrial biodiversity
Understanding the distribution of life’s variety has driven naturalists and scientists for centuries, yet this has been constrained both by the available data and the models needed for their analysis. Here we compiled data for over 67,000 marine and terrestrial species and used artificial neural networks to model species richness with the state and variability of climate, productivity, and multiple other environmental variables. We find terrestrial diversity is better predicted by the available environmental drivers than is marine diversity, and that marine diversity can be predicted with a smaller set of variables. Ecological mechanisms such as geographic isolation and structural complexity appear to explain model residuals and also identify regions and processes that deserve further attention at the global scale. Improving estimates of the relationships between the patterns of global biodiversity, and the environmental mechanisms that support them, should help in efforts to mitigate the impacts of climate change and provide guidance for adapting to life in the Anthropocene
Satellite-Based Evidence for Shrub and Graminoid Tundra Expansion in Northern Quebec from 1986-2010
Global vegetation models predict rapid poleward migration of tundra and boreal forest vegetation in response to climate warming. Local plot and air-photo studies have documented recent changes in high-latitude vegetation composition and structure, consistent with warming trends. To bridge these two scales of inference, we analyzed a 24-year (1986-2010) Landsat time series in a latitudinal transect across the boreal forest-tundra biome boundary in northern Quebec province, Canada. This region has experienced rapid warming during both winter and summer months during the last forty years. Using a per-pixel (30 m) trend analysis, 30% of the observable (cloud-free) land area experienced a significant (p < 0.05) positive trend in the Normalized Difference Vegetation Index (NDVI). However, greening trends were not evenly split among cover types. Low shrub and graminoid tundra contributed preferentially to the greening trend, while forested areas were less likely to show significant trends in NDVI. These trends reflect increasing leaf area, rather than an increase in growing season length, because Landsat data were restricted to peak-summer conditions. The average NDVI trend (0.007/yr) corresponds to a leaf-area index (LAI) increase of ~0.6 based on the regional relationship between LAI and NDVI from the Moderate Resolution Spectroradiometer (MODIS). Across the entire transect, the area-averaged LAI increase was ~0.2 during 1986-2010. A higher area-averaged LAI change (~0.3) within the shrub-tundra portion of the transect represents a 20-60% relative increase in LAI during the last two decades. Our Landsat-based analysis subdivides the overall high-latitude greening trend into changes in peak-summer greenness by cover type. Different responses within and among shrub, graminoid, and tree-dominated cover types in this study indicate important fine-scale heterogeneity in vegetation growth. Although our findings are consistent with community shifts in low-biomass vegetation types over multi-decadal time scales, the response in tundra and forest ecosystems to recent warming was not uniform
The Messy Nature of Fiber Spectra: Star-Quasar Pairs Masquerading as Dual Type 1 AGNs
Theoretical studies predict that the most significant growth of supermassive
black holes occurs in late-stage mergers, coinciding with the manifestation of
dual active galactic nuclei (AGNs), and both major and minor mergers are
expected to be important for dual AGN growth. In fact, dual AGNs in minor
mergers should be signposts for efficient minor merger-induced SMBH growth for
both the more and less massive progenitor. We identified two candidate dual
AGNs residing in apparent minor mergers with mass ratios of 1:7 and
1:30. SDSS fiber spectra show broad and narrow emission lines in the
primary nuclei of each merger while only a narrow [O III] emission line and a
broad and prominent H/[N II] complex is observed in the secondary
nuclei. The FWHMs of the broad H lines in the primary and secondary
nuclei are inconsistent in each merger, suggesting that each nucleus in each
merger hosts a Type 1 AGN. However, spatially-resolved LBT optical spectroscopy
reveal rest-frame stellar absorption features, indicating the secondary sources
are foreground stars and that the previously detected broad lines are likely
the result of fiber spillover effects induced by the atmospheric seeing at the
time of the SDSS observations. This study demonstrates for the first time that
optical spectroscopic searches for Type 1/Type 1 pairs similarly suffer from
fiber spillover effects as has been observed previously for Seyfert 2 dual AGN
candidates. The presence of foreground stars may not have been clear if an
instrument with more limited wavelength range or limited sensitivity had been
used.Comment: 15 pages including appendix and references, 6 figures, 1 table.
Accepted for publication in Ap
Scalar Glueball Mass Reduction at Finite Temperature in SU(3) Anisotropic Lattice QCD
We report the first study of the glueball properties at finite temperatures
below T_c using SU(3) anisotropic lattice QCD with beta=6.25, the renormalized
anisotropy xi \equiv a_s/a_t = 4 and 20^3 \times N_t
(N_t=35,36,37,38,40,43,45,50,72) at the quenched level. From the temporal
correlation analysis with the smearing method, about 20 % mass reduction is
observed for the lowest scalar glueball as m_G(T)=1250 \pm 50MeV for 0.8 T_c <
T < T_c in comparison with m_G \simeq 1500 \sim 1700MeV at T \simeq 0.Comment: This is the second revised version using more gauge configurations. 5
pages, Latex2e, 5 figure
The Color of Childhood: The Role of the Child/Human Binary in the Production of Anti-Black Racism
The binary between the figure of the child and the fully human being is invoked with regularity in analyses of race, yet its centrality to the conception of race has never been fully explored. For most commentators, the figure of the child operates as a metaphoric or rhetorical trope, a non-essential strategic tool in the perpetuation of White supremacy. As I show in the following, the child/human binary does not present a contingent or merely rhetorical construction but, rather, a central feature of racialization. Where Black peoples are situated as objects of violence it is often precisely because Blackness has been identified with childhood and childhood is historically identified as the archetypal site of naturalized violence and servitude. I proceed by offering a historical account of how Black peoples came to inherit the subordination and dehumanization of European childhood and how White youth were subsequently spared through their partial categorization as adults
Scalar Mesons in a Chiral Quark Model with Glueball
Ground-state scalar isoscalar mesons and a scalar glueball are described in a
U(3)xU(3) chiral quark model of the Nambu--Jona-Lasinio (NJL) type with 't
Hooft interaction. The latter interaction produces singlet-octet mixing in the
scalar and pseudoscalar sectors. The glueball is introduced into the effective
meson Lagrangian as a dilaton on the base of scale invariance. The mixing of
the glueball with scalar isoscalar quarkonia and amplitudes of their decays
into two pseudoscalar mesons are shown to be proportional to current quark
masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and
the glueball and their main modes of strong decay are described.Comment: 10 pages, LaTeX text, requires svjour.cls and svepj.cl
Multi-wavelength observations of SDSS J105621.45+313822.1, a broad-line, low-metallicity AGN
In contrast to massive galaxies with Solar or super-Solar gas phase
metallicities, very few Active Galactic Nuclei (AGN) are found in
low-metallicity dwarf galaxies. Such a population could provide insight into
the origins of supermassive black holes. Here we report near-infrared
spectroscopic and X-ray observations of SDSS J105621.45+313822.1, a low-mass,
low-metallicity galaxy with optical narrow line ratios consistent with star
forming galaxies but a broad H line and mid-infrared colors consistent
with an AGN. We detect the [Si VI] 1.96m coronal line and a broad
Pa line with a FWHM of ~km~s. Together with the
optical broad lines and coronal lines seen in the SDSS spectrum, we confirm the
presence of a highly accreting black hole with mass ~M, with a bolometric luminosity of
~erg~s based on the coronal line luminosity, implying a
highly accreting AGN. Chandra observations reveal a weak nuclear point source
with ~erg~s,
orders of magnitude lower than that predicted by the mid-infrared
luminosity, suggesting that the AGN is highly obscured despite showing broad
lines in the optical spectrum. The low X-ray luminosity and optical narrow line
ratios of J1056+3138 highlight the limitations of commonly employed diagnostics
in the hunt for AGNs in the low metallicity low mass regime.Comment: 13 pages, 6 figures, accepted to Ap
Glueball Properties at Finite Temperature in SU(3) Anisotropic Lattice QCD
The thermal properties of the glueballs are studied using SU(3) anisotropic
lattice QCD with beta=6.25, the renormalized anisotropy xi=a_s/a_t=4 over the
lattice of the size 20^3\times N_t with N_t = 24, 26, 28, 30, 33, 34, 35, 36,
37, 38, 40, 43, 45, 50, 72 at the quenched level. To construct a suitable
operator on the lattice, we adopt the smearing method, and consider its
physical meaning in terms of the operator size. First, we construct the
temporal correlators G(t) for the 0^{++} and 2^{++} glueballs, using more than
5,000 gauge configurations at each temperature. We then measure the pole-mass
of the thermal glueballs from G(t). For the lowest 0^{++} glueball, we observe
a significant pole-mass reduction of about 300 MeV near T_c or m_G(T\simeq T_c)
\simeq 0.8 m_G(T\sim 0), while its size remains almost unchanged as rho(T)
\simeq 0.4fm. Finally, for completeness, as an attempt to take into account the
effect of thermal width Gamma(T) at finite temperature, we perform a more
general new analysis of G(t) based on its spectral representation. By adopting
the Breit-Wigner form for the spectral function rho(omega), we perform the
best-fit analysis as a straightforward extension to the standard pole-mass
analysis. The result indicates a significant broadening of the peak as Gamma(T)
\sim 300 MeV as well as rather modest reduction of the peak center of about 100
MeV near T_c for the lowest 0^{++} glueball. The temporal correlators of the
color-singlet modes corresponding to these glueballs above T_c are also
investigated.Comment: This is the revised version using more gauge configurations near T_c.
25 pages, Latex2e, 22 figure
Anatomy of ethylene-induced floral-organ abscission in Chamelaucium uncinatum (Myrtaceae)
Postharvest abscission of Geraldton waxflower (Chamelaucium uncinatum Schauer) flower buds and flowers is ethylene-mediated. Exposure of floral organs to exogenous ethylene (1 mu L L-1) for 6 h at 20 degrees C induced separation at a morphologically and anatomically distinct abscission zone between the pedicel and. oral tube. Flower buds with opening petals and flowers with a nectiferous hypanthium were generally more responsive to exogenous ethylene than were flower buds enclosed in shiny bracteoles and aged (senescing) flowers. The anatomy of abscission-zone cells did not change at sequential stages of floral development from immature buds to aged flowers. The zone comprised a layer of small, laterally elongated-to-rounded, closely packed and highly protoplasmic parenchyma cells. Abscission occurred at a two- to four-cell-wide separation layer within the abscission zone. The process involved degradation of the middle lamella between separation layer cells. Following abscission, cells on both the proximal and distal faces of the separation layer became spherical, loosely packed and contained degenerating protoplasm. Central vascular tissues within the surrounding band of separation layer cells became torn and fractured. For flower buds, bracteoles that enclose the immature floral tube also separated at an abscission zone. However, this secondary abscission zone appeared less sensitive to ethylene than the primary ( central). oral-tube abscission zone as bracteoles generally only completely abscised when exposed to 10 mu L L-1 ethylene for the longer period of 24 h at 20 degrees C. The smooth surfaces of abscised separation-layer cells suggest that hydrolase enzymes degrade the middle lamella between adjacent cell walls
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